EP0790356A1

EP0790356A1 - Controller for excavators

Info

Publication number: EP0790356A1
Application number: EP96928698A
Authority: EP
Inventors: Kouji Tsukubaryou Funato
Original assignee: Hitachi Construction Machinery Co Ltd
Current assignee: Hitachi Construction Machinery Co Ltd
Priority date: 1995-08-31
Filing date: 1996-08-30
Publication date: 1997-08-20
Anticipated expiration: 2016-08-30
Also published as: JP3068772B2; CN1070973C; CN1166191A; DE69621767D1; JPH0967829A; EP0790356A4; EP0790356B1; KR970707352A; KR100439892B1; WO1997008395A1; DE69621767T2

Abstract

In order to improve the durability of a tooth edge of an excavator and thereby an excavation efficiency thereof as well, a penetration force control unit (70) controls a hydraulic winch HWD so that a detected penetration force attains a set level, whereby the speed of the excavator (10) is controlled. A descending speed control unit (50) is adapted to control the hydraulic winch HWD so that a detected descending speed attains a set level, whereby the speed of the excavator (10) is controlled. When a detected level of the descending speed exceeds a predetermined level during a control operation of the penetration force control unit (70), a selection unit (80) shifts the control operation to that by the descending speed control unit (50). The descending speed control unit (50) is adapted to control the descending speed by a proportional integration control operation, while the penetration force control unit (70) is adapted to control the penetration force by a proportional differentiation control operation.

Description

Technical Field

The present invention relates to a controller that controls the penetration force (excavating load) and the penetration speed (descending speed) of an excavator at preset values.

Background Art

Controllers for excavators which are employed in the continuous wall method and in the earth drill excavation method include the excavating speed controller for excavators disclosed in Japanese Patent Publication No. 7 (1995)-26414. In this speed controller, which is provided with a speed control unit that controls the speed of a winch such that the excavator descends at a predetermined speed by changing the speed reduction ratio of the winch and a load control unit that controls the speed of a winch such that the load at the tooth edge is at an upper limit value by changing the speed reduction ratio of the winch, the operation is switched to load control if the load at the tooth edge exceeds the upper limit value during speed controlled operation. With this method, if, due to consideration of the durability of the tooth edge of the excavator, the upper limit value for the load at the tooth edge is set too low, excavation will be performed under load control even in relatively soft soil, at an excavating speed that is too high for the available soil discharge capacity.
In addition, there is a penetration force and speed controller for excavators in the known art that is disclosed in Japanese Patent Publication No. 3(1991)-80216. With this speed controller, which is provided with a control unit that controls the speed of a winch such that the excavator descends at a predetermined speed by adjusting the braking force and a load control unit that controls the speed of the winch such that the penetration force is at a predetermined level of penetration force by adjusting the braking force, the operation is switched to speed control if the speed exceeds a specific value during load control operation. With this method, the upper limit value of the excavating speed may be determined in correspondence to the capacity for discharging excavated soil, and even if the load at the tooth edge is set at a low level due to consideration of the excavation efficiency, the discharge of the excavated soil is performed smoothly when the operation is switched to speed control. Moreover, deterioration in the durability of the tooth edge of the excavator is prevented.
However, specific circuit structures for speed control and penetration force control are not disclosed in Japanese Patent Publication No. 3(1991)-80216. Japanese Patent Publication No. 7(1995)-26414 discloses an art in which speed control is constituted of proportional integration control or proportional integration control combined with feed-forward control and tooth edge load (penetration force) control is constituted of proportional control. Thus, the possibility of adopting this control method in the controller disclosed in Japanese Patent Publication No. 3(1991)-80216 may be contemplated. However, since, in tooth edge load control, the tooth edge load is controlled with an upper limit value by adjusting the descending speed of an excavator that weighs several tens of tons, good response characteristics cannot be achieved through proportional control or proportional integration control, making it impractical. In addition, since the operation switches from load control (penetration force control) to speed control or from speed control to load control by using a predetermined excavating speed value as a reference, there exists the likelihood of the control system hunting in the vicinity of the predetermined switching speed value.
An object of the present invention is to provide a controller for excavators that achieves an improvement in the durability of the tooth edge of an excavator and an improvement in excavation efficiency.

Disclosure of Invention

The controller for excavators according to the present invention comprises a winch that causes an excavator to ascendant descend, a penetration force detection means that detects the penetration force of the excavator, a penetration force control means that controls the winch such that the penetration force detected by the penetration force detection means attains a predetermined level of penetration force, a descending speed detection means that detects the descending speed of the excavator, a descending speed control means that controls the winch such that the descending speed detected by the descending speed detection means attains a predetermined level of descending speed and a selection means that implements a shift to control performed by the descending speed control means when the detected value for the descending speed exceeds a specific value during control performed by the penetration force control means. The descending speed control means controls the descending speed through proportional integration control and the penetration force control means controls the penetration force through proportional differentiation control.
In the controller for excavators according to the present invention, the penetration force control means controls the speed of an excavator by controlling a hydraulic winch such that the penetration force detected attains a predetermined level of penetration force. The descending speed control means controls the speed of the excavator by controlling the hydraulic winch to ensure that the detected descending speed attains a predetermined level of descending speed. The selection means implements a shift to control performed by the descending speed control means when the detected value of the descending speed exceeds a specific value during control performed by the penetration force control means. The descending speed control means controls the descending speed through proportional integration control and the penetration force control means controls the penetration force through proportional differentiation control.
Alternatively, the controller for excavators according to the present invention may comprise a hydraulic source that discharges pressure oil, a winch hydraulic motor that is connected with the hydraulic source through a first oil passage and a second oil passage, control valves that are provided in the middle of the first oil passage and the second oil passage, a counter balance valve that is provided in the second oil passage which is the return side for lowering the excavator, a pressure adjustment means that adjusts the pressure in the second oil passage between the counter balance valve and the hydraulic motor, a penetration force detection means that detects the penetration force of the excavator, a penetration force control means that controls the pressure adjustment means such that the difference between the penetration force detected by the penetration force detection means and a predetermined level of penetration force is zero, a descending speed detection means that detects the descending speed of the excavator, a descending speed control means that controls the pressure adjustment means such that the difference between the descending speed detected by the descending speed detection means and a predetermined level of descending speed is zero and a selection means that implements a shift to control performed by the descending speed control means when the detected value of the descending speed exceeds a specific value during control performed by the penetration force control means.
In the controller for excavators according to the present invention described above, the selection means implements a shift to control performed by the descending speed control means when the detected value of the descending speed exceeds a specific value during control performed by the penetration force control means. Speed control is implemented through adjustment of the pressure in the second oil passage which is performed by the pressure adjustment means. When the pressure in the oil passage is reduced, the rotating speed of the hydraulic motor increases, whereas when the pressure is increased, the rotating speed is reduced.
It is desirable that the descending speed control means should control the descending speed through proportional integration control and that the penetration force control means should control the penetration force through proportional differentiation control.
Alternatively, the selection means may implement a shift to control performed by the descending speed control means when the detected value of the descending speed exceeds a first specific value during control performed by the penetration force control means and may implement a shift to control performed by the penetration force control means when, at least, the detected value of the descending speed is at or lower than a second specific value which is smaller than the first specific value.
Alternatively, the controller for excavators according to the present invention may comprise a winch that raises and lowers an excavator, a penetration force detection means that detects the penetration force of the excavator, a penetration force control means that controls the winch such that the penetration force detected by the penetration force detection means attains a predetermined level of penetration force, a descending speed detection means that detects the descending speed of the excavator, a descending speed control means that controls the winch such that the descending speed detected by the descending speed detection means attains a predetermined level of descending speed and a selection means that implements a shift to control performed by the descending speed control means when the detected value of the descending speed exceeds a first specific value during control performed by the penetration force control means and implements a shift to control performed by the penetration force control means when, at least, the detected value of the descending speed is at or lower than a second specific value which is smaller than the first specific value.
In the controller for excavators described above, the conditional values for switching from penetration force control to speed control and for switching in the reverse direction introduce hysteresis. After the operation shifts to speed control with the detected value exceeding the first specific value, the operation is switched to penetration force control if the descending speed becomes reduced to the second specific value which is smaller than the first specific value.
The penetration force detection means described above may be constituted of an excavating load detection means that detects, as a penetration force, the true value of the excavating load imposed upon the excavator as it excavates soil.
Furthermore, the controller for excavators according to the present invention may comprise a winch that raises and lowers an excavator, an excavating load detection means that detects the true value of the excavating load imposed upon the excavator as it excavates soil, an excavating load control means that controls the winch such that the excavating load detected by the excavating load detection means attains a predetermined level of excavating load, a descending speed detection means that detects the descending speed of the excavator, a descending speed control means that controls the winch such that the descending speed detected by the descending speed detection means attains a predetermined level of descending speed and a selection means that implements a shift to control performed by the descending speed control means when the detected value of the descending speed exceeds a specific value during control performed by the excavating load control means.
In this controller for excavators, the load that is truly imposed upon the excavator is taken as the penetration force. The penetration force control means controls the speed of the excavator by controlling the winch in such a manner that the detected penetration force attains a predetermined level of penetration force. The descending speed control means controls the speed of the excavator by controlling the hydraulic winch in such a manner that the detected descending speed attains a predetermined level of descending speed. When the detected value of the descending speed exceeds a specific value during control performed by the penetration force control means, the selection means implements a shift to control performed by the descending speed control means.
As an alternative, the selection means may implement switching to speed control performed by the descending speed control means when the detected value of the penetration force is at or less than a first specific penetration force value, implement switching to penetration force control performed by the penetration force control means when the detected value of the penetration force exceeds the first specific penetration force value during speed control, implement a shift to control performed by the descending speed control means when the detected value of the descending speed exceeds a first specific speed value during penetration force control and implement a shift to control performed by the penetration force control means when the detected value of the descending speed is at or less than a second specific speed value that is smaller than the first specific speed value and the detected value of the penetration force is at or more than a second specific penetration force value that is larger than the first specific penetration force value.
As an alternative, the selection means may implement switching to speed control performed by the descending speed control means when the detected value of the penetration force is at or less than a first specific penetration force value, implement switching to penetration force control performed by the penetration force control means when detected value of the penetration force exceeds the first specific penetration force value during speed control, implement a shift to control performed by the descending speed control means when the detected value of the descending speed exceeds a first specific speed value during penetration force control and implement a shift to control performed by the penetration force control means when the detected value of the descending speed is at or less than a second specific speed value that is smaller than the first specific speed value and the detected value of the penetration force is at or more than a second specific penetration force value which is larger than the first specific penetration force value.
The controller for excavators according to the present invention achieves the following advantages.
Since the descending speed control means that controls the speed of the excavator such that the detected descending speed attains the predetermined level of descending speed performs control of the descending speed through proportional integration control and the penetration force control means that controls the speed of the excavator such that the detected excavating load attains a predetermined level of excavating load performs control of the descending speed through proportional differentiation control, the accuracy and stability of the speed control unit improves and the response characteristics of the penetration force control means are improved, thereby improving the operability while lowering the excavator at crawling speed.
By implementing crawling speed control through adjustment of the pressure in the oil passage where the counter balance valve for the hydraulic winch is provided, it becomes possible to make the apparatus more compact at a lower production cost compared to the case in which a speed reducing mechanism with two speed reduction ratios, i.e., high and low, is provided. In addition, unlike an apparatus in which crawling speed is obtained through adjustment of mechanical braking force, no heat is generated at the braking device, thereby eliminating the resulting reduction in durability and the resulting deterioration in maintainability, which, in turn, achieves a reduction both in initial costs and in running costs.
Furthermore, since hysteresis is introduced in the switching threshold values for switching between penetration force control and speed control, it becomes possible to prevent hunting, thereby achieving an improvement in operability. By detecting the true excavating load that is imposed upon the excavator to be used for penetration force control, it becomes possible to accurately detect the excavating load, thereby achieving a high degree of accuracy in excavation.

Brief Discription of Drawing

FIG. 1 is a block diagram showing an example of the controller for excavators according to the present invention;
FIG. 2 is a block diagram showing a detailed example of the controller shown in FIG. 1;
FIG. 3 is a flowchart illustrating the procedure of selection implemented by the selection unit of the controller;
FIGS. 4A - 4F are graphs that illustrate the switching conditions for switching between penetration force control and speed control;
FIG. 5 is a graph showing the N value and the excavating speed; and
FIG. 6 is a block diagram of the controller in another embodiment.

Best Mode for Carrying Out the Invention

-First Embodiment-

In reference to FIGS. 1 - 5 an explanation is given of the present invention when it is employed in an excavator that employs a crawler crane mounted with a hydraulic winch.
In the first embodiment, an excavator is raised and lowered by a hydraulic winch HWD. In FIG. 1, pressure oil at a hydraulic source 1, which is constituted of a hydraulic pump and a relief valve, is led to a hydraulic motor 3 via a control valve 2. The control valve 2 and the hydraulic motor 3 are connected with each other via oil passages 4 and 5, and in the oil passage 5, a counter balance valve 6, which is constituted of a pressure regulating valve 6a and a check valve 6b, is provided. The pressure regulating valve 6a opens in correspondence to the pressure in one of the oil passages, i.e., the oil passage 4, and when there is no pressure in the oil passage 4 it closes to prevent the winch from running away. The output speed from the hydraulic motor 3 is reduced by a speed reduction unit 7 to drive and rotate a windup drum 8. Any of the following, i.e., a manual switching method, a hydraulic pilot switching method, an electromagnetic switching method and the like, may be adopted to operate the control valve 2. The above is the explanation of the hydraulic winch HWD.
The windup drum 8 takes up and feeds out a wire rope 9 to raise and lower an excavator 10. The wire rope 9 is drawn around via sheaves 12 on a boom 11 and the rope speed, i.e., the ascending / descending speed of the excavator 10, is detected by detecting the rotation rate of the sheaves 12 with an excavating speed detector 21. The boom derricking force of the boom 11 is detected by a boom derricking force detector 22 and the angle of the boom 11 is detected by a boom angle meter 23 so that a hoisting load can be calculated based upon the boom derricking force and the boom angle. Then the penetration force is calculated by subtracting the tare weight of the excavator 10 from the hoisting load. It is to be noted that the penetration force is referred to as both tooth edge load and excavating load. Also, reference number 13 indicates a makeup valve which replenishes pressure oil from a tank to prevent the pressure in the oil passage 4 from becoming negative.
In addition, in the first embodiment, a pressure control device PCD, is provided for adjusting the pressure in the oil passage 5 to fine-tune the speed of the hydraulic motor 3. This pressure control device PCD is provided with an electromagnetic proportional valve 31 located between the oil passage 4 and the oil passage 5 that is operated toward the open side when the pressure in the oil passage 5 is reduced, a check valve 32 that prohibits the flow of pressure oil from the oil passage 4 to the oil passage 5, a relief valve 33 that applies back-pressure to the return oil from the electromagnetic proportional valve 31, an electromagnetic proportional valve 34 that is operated toward the open side when the pressure in the oil passage 5 is increased, a check valve 35 that ensures that the pressure oil in the oil passage 5 does not flow toward the electromagnetic proportional valve 34 and an electromagnetic open / close valve 36 that cuts off the oil path between the oil passage 4 and the oil passage 5.
The electromagnetic proportional valves 31 and 34 and the electromagnetic open / close valve 36 are opened and closed with a command signal from a controller 40. The controller 40 is connected with the excavating speed detector 21, the boom angle meter 23, the boom derricking force detector 22, an upper limit speed level setting unit 41 that sets an excavating upper limit speed level for the excavator 10, an upper limit load level setting unit 42 that sets an upper limit excavation load level for the excavator 10, a mode switch 43 that specifies a crawling speed mode employing the pressure control device PCD and an excavator tare weight setting unit 44 that sets the tare weight of the excavator 10. If the crawling speed mode is not selected at the mode switch 43, the electromagnetic open / close valve 36 is closed.
The present invention includes control whereby when the excavating speed exceeds a first specific value (upper limit speed level) during penetration force control, the operation is switched to speed control whereas when the excavating speed is at or lower than a second specific value (first specific value X 0.7) during speed control, the operation is switched to penetration force control, and the controller 40 is structured as shown in FIG. 2.
FIG. 2 is a block diagram illustrating the processing performed by the controller 40. The controller 40 is provided with a true hoisting load calculation unit 45, a speed control unit 50, a the penetration force control unit 70, a selection unit 80 and an output unit 90. The true hoisting load calculation unit 45, into which the boom angle detected by the boom angle meter 23 and the boom derricking force detected by the boom derricking force detector 22 are input, calculates a true hoisting load by using an arithmetic expression of the known art.
The speed control unit 50, which is provided with a subtractor 51 that calculates a difference ΔV between the predetermined upper limit speed level Vt output from the upper limit speed level setting unit 41 and a true speed Vr output from the excavating speed detector 21, a multiplier 52 that multiplies the difference ΔV by a gain Kp an integrator 53 that integrates the difference ΔV, a multiplier 54 that multiplies the output from the integrator 53 by a gain Ki and an adder 55 that adds an output Ki·ΣΔV from the multiplier 54 to an output Kp·ΔV from the multiplier 52 to output a speed control command Nv, outputs a speed control command signal Nv that corresponds to the difference between the detected excavating speed Vr and the predetermined upper limit speed level Vt such that the excavating speed attains the predetermined upper limit speed level set by the upper limit speed level setting unit 41. As has been explained above, the speed control unit 50 employs a proportional integration control method.
The penetration force control unit 70, which is provided with a subtractor 71 that calculates a difference Wr between a true hoisting load Wt output from the true hoisting load calculation unit 45 and the tare weight Wo set at the excavator tare weight setting unit 44, a subtractor 72 that calculates a difference ΔW between an output Wr from the subtractor 71 and an upper limit value WL for the penetration force, a multiplier 73 that multiplies the difference ΔW by a gain Kpw, a storage device 74 that stores in memory the difference ΔW as a previous difference ΔWOL, a subtractor 75 that calculates a difference ΔWD between the previous difference ΔWOL stored in the storage device 74 and a current difference ΔW, a multiplier 76 that multiplies the difference ΔWD by a gain Kdw and an adder 77 that adds an output Kdw·ΔWD from the multiplier 76 to an output Kpw·ΔW from the multiplier 73 to output a penetration force control command Nw, outputs a penetration force control signal Nw that corresponds to the difference between the detected excavating load Wr and the upper limit value WL so that the excavating load attains the upper limit value WL set by the upper limit load level setting unit 42. As has been explained above, the penetration force control unit 70 employs a proportional differentiation control system.
The selection unit 80 selects either the output Nv from the speed control unit 50 or the output Nw from the penetration force control unit 70 and inputs the selected output to the output unit 90. According to the present invention, penetration force control is selected when starting up the apparatus, and the control mode is switched between penetration force control and excavating speed control in correspondence to the excavating speed and the excavating load. There is hysteresis introduced in the selecting operation performed by the selection unit 80, and the control mode is switched as illustrated in the flowchart in FIG. 3, for instance.
The control mode switching is explained in reference to the flowchart shown in FIG. 3. In the initial state, the control mode is set for penetration force control and a status flag is set to 0 in step S1. If crawling speed mode is set in step S2, a decision is made in step S3 in regard to the previous control status. If the previous status indicates that penetration force control is in effect, the operation proceeds to step S4, and if the calculated excavating load Wr is less than (upper limit value WL / 4), the operation proceeds to step S9 to switch to excavating speed control. The status flag is set to 1 at this time. The flow described above indicates that when the crawling speed mode is set at startup and the operation has been switched to penetration force control, the operation is switched to speed control if the excavating load Wr is less than (excavating upper limit value WL / 4).
If the operation proceeds from step S1 to steps S2, S3, S4 and S5 after startup, and if the excavating speed Vr exceeds the upper limit speed level Vt and the excavating load Wr is less than the upper limit load level WL in step S5, the operation is switched to speed control in step S9. The flow described above indicates that when, with crawling speed mode set at startup, the operation has been switched to penetration force control, the operation will be switched to speed control if the excavating load Wr is at or more than (upper limit value WL / 4) and the excavating speed Vr exceeds the excavating upper limit speed level Vt.
Then, in step S3, which follows step S9 in which the operation has been switched to speed control, the status flag is set to 1 and the operation proceeds to step S7. If the calculated excavating load Wr is at or less than (upper limit load level WL / 2), the speed control is continuously executed in step S9. The flow described above indicates that when the operation has been switched from penetration force control to speed control, speed control is sustained if the excavating load Wr is at or less than (excavating upper limit value WL / 2). Also, if the excavating load Wr exceeds (upper limit load level WL / 2) in step S7, the operation proceeds to step S8 in which a decision is made as to whether or not the excavating load Wr is less than the upper limit load level WL and a decision is made as to whether or not the excavating speed Vr exceeds (upper limit speed level Vt X 0.7). If affirmative decisions are made in both queries in step S8, the speed control is continuously executed in step S9. The flow described above indicates that when the operation has been switched from penetration force control to speed control, speed control is sustained even if the excavating load Wr exceeds (excavating upper limit value WL / 2) as long as the excavating speed Vr is greater than (upper limit speed level Vt X 0.7). If a negative decision is made in either query in step S8, i.e., if the excavating speed V is at or less than (upper limit speed level Vt X 0.7), for instance, the operation proceeds to step S6 to switch to penetration force control. The status flag is set to 0 at this time. The flow described above indicates that when the operation has been switched from penetration force control to speed control, the operation will be switched from speed control to penetration force control if the excavating load Wr exceeds (excavating upper limit value WL / 2) and the excavating speed Vr is at or less than (upper limit speed level Vt X 0.7).
The operation described above may be summed up as follows.

(i) Excavation in progress under penetration force control

1. The operation is switched to speed control if the excavating load Wr is less than (excavating upper limit value WL / 4). This corresponds to the operation proceeding to step S9 from steps S1 - S4 in the flowchart in FIG. 3, and is represented by the hatched areas in FIG. 4A.
2. The operation is switched to speed control when the excavating load Wr is at or more than the excavating upper limit value WL / 4 and the excavating speed Vr exceeds the upper limit speed level Vt. This corresponds to the operation proceeding to step S9 from steps S1 - S5 in the flowchart in FIG. 3, and is represented by the hatched area in FIG. 4B.
3. Penetration force control is sustained when the excavating load Wr is at or more than the excavating upper limit value WL / 4 and the excavating speed Vr is at or less than the upper limit speed level Vt. This corresponds to the operation proceeding to step S6 from steps S1 - S5 in the flowchart in FIG. 3, and is represented by the hatched area in FIG. 4C.
4. Penetration force control is sustained when the excavating load Wr is at or more than the excavating upper limit value WL and the excavating speed Vr is at or less than the upper limit speed level Vt. This corresponds to the operation proceeding from step S5 to step S6 in the flowchart in FIG. 3, and is represented by the hatched area in FIG. 4D.

(ii) Operation in progress under speed control

1. The operation is switched to penetration force control when the excavating load Wr exceeds the excavating upper limit value WL / 2 and the excavating speed Vr is at or less than (upper limit speed level Vt 0.7). This corresponds to the operation proceeding from step S7 to step S8 then to step S6 in the flowchart in FIG. 3, and is represented by the hatched area in FIG. 4E.
2. Speed control is sustained when the excavating load Wr is at or less than the excavating upper limit value WL / 2 (corresponding to the operation proceeding from step S7 to step S9 in the flowchart in FIG. 3), and speed control is also sustained even when the excavating load Wr exceeds the excavating upper limit value WL / 2 as long as the excavating speed Vr exceeds (upper limit speed level Vt×0.7) (corresponding to the operation proceeding from step S7 to step S8 and then to step S9 in the flowchart in FIG. 3). Thus, after the operation is switched from penetration force control to speed control, the range of the speed control is expanded as shown in FIG. 4F by the hysteresis.

In other words, as threshold values related to the speed, the upper limit speed level Vt is set for a first threshold value and (upper limit speed level Vt×0.7) is set for a second threshold value, and the operation is switched from penetration force control to speed control when the excavating speed Vr which is detected during penetration force control exceeds the upper limit value (first set value Vt1). When the excavating speed Vr falls to or under the second specific value Vt2 (= upper limit speed level Vt×0.7) which is smaller than the first specific value Vt1 and the excavating load Wr exceeds (upper limit load level WL / 2) during speed control, the operation is switched to penetration force control.
As for threshold values related to the excavating load, (upper limit load level WL / 4) is set for a first threshold value and (upper limit load level WL / 2) is set for a second threshold value. The operation is switched to speed control when the excavating load Wr detected during penetration force control is less than the first threshold value WL / 4, whereas the operation is switched to penetration force control when the excavating load Wr exceeds the second threshold value WL / 2 and the speed is at or less than (upper limit speed level Vt×0.7) during speed control.
The output unit 90 is provided with an integrator 91 that integrates the output signal from the selection unit 80, a sign decision maker 92 that makes a decision as to the sign of an output Nc from the integrator 91, a constant current amplifier 93 that outputs the output Nc from the integrator 91 as a specific voltage with a constant current and a switch 94 whose contact point a or b is closed depending upon the results of the decision making supplied by the sign decision maker 92. The contact point a is connected with the electromagnetic proportional valve 34 and the contact point b is connected with the electromagnetic proportional valve 31. A signal that corresponds to the speed difference signal Nv or the load difference signal Nw is applied to the electromagnetic proportional valve 31 or 34 via the contact point a or the contact point b.
The operation of the controller for excavators which is structured as described above is explained in detail.
After selecting the crawling speed mode with the mode switch 43 and operating the control valve 2 to a neutral position (in some cases, it may be opened at a specific quantity toward the descending side), the operator sets an upper limit value Vt for the excavating speed of the excavator 10 with the upper limit speed level setting unit 41, sets an upper limit value WL for the excavating load with the upper limit excavation load level setting unit 42 and sets the tare weight Wo of the excavator 10 with the tare weight setting unit 44.
The true hoisting load calculation unit 45 calculates a true hoisting load Wt based upon the boom derricking force detected by the boom derricking force detector 22 and the boom angle detected by the boom angle meter 23 by employing an arithmetic method of the known art. The subtractor 71 calculates the excavating load Wr that the excavator 10 will be subject to from the soil based upon the difference between the true hoisting load Wt and the tare weight Wo of the excavator 10, and then the subtractor 72 calculates the difference ΔW between the upper limit load level WL set by the upper limit excavation load level setting unit 42 and the excavating load Wr. The multiplier 73 outputs a value achieved by multiplying the difference ΔW by the gain Kpw. The difference ΔW is stored in memory in the storage device 74 as a previous difference ΔWOL, and the difference ΔWD between the current difference ΔW and the previous difference ΔWOL is calculated by the subtractor 75. The multiplier 76 then outputs a value achieved by multiplying the difference ΔWd by the gain Kdw. The adder 77 outputs an excavation control command signal Nw which is constituted of the result of adding Kdw·ΔWD which is a differential term to Kpw·ΔW which is a proportional term.
The operation of the speed control unit 50 is as follows. A difference ΔV between the descending speed Vr detected by the excavating speed detector 21 and the upper limit value Vt set by the upper limit speed level setting unit 41 is calculated by the subtractor 51. The multiplier 52 outputs Kp·ΔV which is achieved by multiplying the difference ΔV by a gain Kp. The integrator 53 integrates the difference ΔV and the multiplier 54 multiplies the integrated value ΣΔV by a gain Ki. The subtractor 55 outputs a speed control command signal Nv by adding an integral term Ki·ΣΔV which is the output from the multiplier 54 to a proportional term Kp·ΔV which is the output from the multiplier 52.
The selection unit 80 selects either the speed control command signal Nv or the penetration force control command signal Nw as described earlier and inputs the selected signal to the output unit 90.
When the contact point a of the selection unit 80 is closed (penetration force control):
When the detected excavating load Wr is at or less than the upper limit value WL, the excavation control command signal Nw which is input to the output unit 90 is set to positive and the contact point b of the switch 94 is closed by the sign decision maker 92, thereby closing the electromagnetic proportional valve 34 to operate the electromagnetic proportional valve 31 toward the open side, reducing the pressure in the oil passage 5 and increasing the speed of the hydraulic motor 2. As a result, the rotating speed of the drum 8 increases to increase the excavating load of the excavator 10. In other words, by intentionally increasing the quantity of pressure oil leak from the oil passage 5, the hydraulic motor 3 is caused to rotate at a rotation rate that is greater than the crawling speed rotation rate of the hydraulic motor 3 which is effected by a normal quantity of leak from the various hydraulic devices. It is to be noted that the quantity of opening of the electromagnetic proportional valve 31 depends upon the levels of the command signals Nw and Nv. In this context, the crawling speed rotation rate of the hydraulic motor 3 refers to an extremely low rotation rate at which the excavator 10 is lowered at, for instance, 0.5 cm / min.
When the detected excavating load Wr exceeds the upper limit value WL, the excavation control command signal Nw that is input to the output unit 90 is set to negative and the contact point a of the switch 94 is closed by the sign decision maker 92, thereby closing the electromagnetic proportional valve 31 to operate the electromagnetic proportional valve 34 to the open side, increasing the pressure in the oil passage 5 and reducing the speed of the hydraulic motor 3. As a result, the rotation rate of the drum 8 becomes reduced which, in turn, results in a reduction in the excavating load of the excavator 10. In other words, by increasing the pressure in the oil passage 5, a hydraulic brake is applied to the crawling speed rotation of the hydraulic motor 3 which is effected by the leak from the various hydraulic devices to reduce the rotation rate of the hydraulic motor 3.
Through the control described above, excavating load control is implemented by adjusting the speed of the excavator 10 within a range in which the excavating load does not exceed the upper limit value WL. If the descending speed of the excavator 10 exceeds the first specific value Vt during this excavating load control, the selection unit 80, upon its contact point b becoming closed, selects the speed control command Nv from the speed control unit 50.
When the contact point b of the selection unit 80 is closed (speed control):
When the descending speed Vr detected by the excavating speed detector 21 is lower than the predetermined speed Vt that has been set by the upper limit speed level setting unit 41, the speed control unit 50 outputs a positive speed control command Nv. The contact point b of the switch 94 in the output unit 90 becomes closed thereby closing off the electromagnetic proportional valve 34 to operate the electromagnetic proportional valve 31 toward the open side, reducing the pressure in the oil passage 5 and increasing the speed of the hydraulic motor 3. As a result, the rotation rate of the drum 8 increases, which, in turn, increases the descending speed of the excavator 10. It is to be noted that the quantity of opening of the electromagnetic proportional valve 34 depends upon the levels of the command signals Nw and Nv.
If the true excavating speed Vr exceeds the specific speed Vt, the speed control command Nv is set to negative and the contact point a of the switch 94 in he output unit 90 becomes closed, thereby closing off the electromagnetic proportional valve 31 to operate the electromagnetic proportional valve 34 to the open side, increasing the pressure in the oil passage 5 and reducing the speed of the hydraulic motor 3. As a result, the rotation rate of the drum 8 becomes reduced, which, in turn, reduces the descending speed of the excavator 10. Now, if the operation is to be performed with the descending speed of the excavator 10 within the range between the first specific speed Vt and the second specific speed (Vt×0.7) after the true excavating speed Vr exceeds the upper limit value Vt, the control described below is implemented since, as described earlier, the contact point b of the selection unit 80 is closed due to the hysteresis.
The true excavating speed Vr becomes lower than the predetermined speed Vt setting the speed control command Nv to positive. With the contact point b of the switch 94 in the output unit 90 closed, the electromagnetic proportional valve 34 is closed to operate the electromagnetic proportional valve 31 toward the open side, reducing the pressure in the oil passage and increasing the speed of the hydraulic motor 3. As a result, the rotation rate of the drum 8 increases, which, in turn, increases the descending speed of the excavator 10. When the N value of in the soil increases and the descending speed Vr is at or less than the second specific value, i.e., (Vt×0.7), if the excavating load Wr is at or more than (upper limit value / 2) the selection unit 80, with its contact point a closed, selects the excavation control command Nw from the excavation control unit 70.
In the first embodiment described so far, the following advantages are achieved.

1. Since a proportional differentiation control system is adopted in the penetration force control unit 70 and a proportional integration control system is adopted in the speed control unit 50, the response characteristics in excavating load control is improved thereby achieving an improvement in the accuracy of speed control and in the stability in the entire system.
2. Since the excavating load control mode, whereby the excavating load is constant, constitutes a basic mode, the excavating speed is reduced in soil with a high N value and the excavating speed is increased in soil with a low N value, as shown in FIG. 5. Since, in soft soil, when the excavating speed is at or more than a specific value (upper limit value), there is the likelihood of the excavating speed becoming excessively high resulting in excavated soil being discharged at a rate in excess of the capacity of the discharge pump, the operation is switched from excavating load control to speed control. In speed control, since the descending speed of the excavator 10 is controlled to attain the predetermined excavating speed, the soil is discharged as appropriate as long as the upper limit value of the descending speed is set to correspondence to the capacity of the soil discharge pump.
3. Hunting is prevented since the operation is switched from excavating load control to speed control when the descending speed exceeds the first specific value (upper limit value Vt) and the operation is switched to excavating load control when the excavating load exceeds (upper limit value WL / 2) and the descending speed is at or less than the second specific value (upper limit value Vt×0.7) which is lower than the first specific value (upper limit value Vt) during speed control, i.e., since hysteresis is introduced in the threshold values for control switching.
4. Since the hydraulic winch is employed to achieve crawling speed control by adjusting the pressure in the oil passage 5 which is located toward the return side during a wind down, the structure is simplified, making it possible to achieve a reduction in production costs compared to a method in which a crawling speed winch power mechanism constituted of a hydraulic motor and a speed reduction mechanism with a high speed reduction ratio, and a normal speed winch power mechanism constituted of a hydraulic motor and a speed reduction mechanism with a low speed reduction ratio, are provided and the crawling speed winch power mechanism is employed for crawling speed control. Furthermore, while, when a crawling speed is achieved by adjusting the mechanical braking force as in the apparatus disclosed in Japanese Patent Publication No. 3(1991)-80216, problems arise, such as heat generated at the braking device and the resulting reduction in durability, these problems are eliminated in the embodiment explained above. It is to be noted that the tare weight of an excavator employed in the continuous wall method, for instance, is several tens of tons, necessitating the use of a braking device with a large capacity and that the generated heat and the resulting reduction in durability have presented serious problems in practical use.
5. In order to achieve crawling speed control by adjusting the pressure in the oil passage 5 that will be located toward the return side during a wind down, with a hydraulic winch employed, a circuit through which oil is leaked to a tank from an oil path at the hydraulic motor 3 connecting the oil passage 4 and the oil passage 5 and with the electromagnetic proportional valve 31 provided in this circuit, is provided and a circuit that leads pressure oil from the hydraulic source 1 to the oil passage 5, with the electromagnetic proportional valve 34 provided in this circuit, is provided, to adjust the pressure in the oil passage 5 through open / close control of the pair of electromagnetic proportional valves 31 and 34, making it possible to add the crawling speed control device PCD to the hydraulic winch of an existing excavator with ease.

-Second Embodiment-

The apparatus in the second embodiment, which is shown in FIG. 6, dispenses with the pressure control device PCD in the hydraulic winch HWD shown in FIG. 1, with clutches employed to switch between a hydraulic winch high speed drive system HD1 which is employed for regular work and a hydraulic winch crawling speed drive system HD2 which is employed for crawling speed control.
The hydraulic motor high speed drive system HD1 is constituted of the hydraulic motor 3 and a speed reduction unit 7 in FIG. 1, and the hydraulic winch crawling speed drive system HD2 is constituted of a hydraulic motor 3A and a speed reduction unit 7A. The capacity of the hydraulic motor 3A is set smaller than the capacity of the hydraulic motor 3, and the speed reduction ratio of the speed reduction unit 7A is set higher than the speed reduction ratio of the speed reduction unit 7. A clutch 14 is provided between the speed reduction unit 7 and the drum 8 and a clutch 14A is provided between the speed reduction unit 7A and the drum 8. The winch crawling speed drive system HD2 is provided with a hydraulic pump 1A and an electromagnetic proportional control valve 2A which controls the oil quantity and the direction of pressure oil that is supplied from the hydraulic pump 1A to the hydraulic motor 3A.
The operation of the electromagnetic proportional control valve 2A is controlled by a command signal provided by a controller 40A. The controller 40A is structured identically to that shown in FIG. 2, with the individual detection signals input from the excavating speed detector 21, the boom derricking force detector 22 and the boom angle meter 23. In addition, signals and the mode that have been set at the upper limit speed level setting unit 41, the upper limit excavation load level setting unit 42, the tare weight setting unit 44 and the mode set at the mode switch 43 are input.
It is to be noted that while switching between the clutches 14 and 14A may be implemented by a manual operating device (not shown) that engages either one of the clutches and disengages the other clutch, it may also be implemented by disengaging the clutch 14A with the clutch 14 engaged by the controller 40A when the regular speed control mode is selected with the mode switch 43 and by disengaging the clutch 14 with the clutch 14A engaged when crawling speed control mode is selected.
The electromagnetic proportional control valve 2A, with its switching quantity and switching direction controlled by the speed control command Nv or the excavation control command Nw provided by the controller 40A, is controlled in such a manner that when the descending speed of the excavator 10 exceeds the first specific value (upper limit value) during excavating load control the operation is switched to speed control and that when the descending speed is at or less than the second specific value (upper limit value×0.7) during speed control, the operation is switched to excavating load control.
While, in the two embodiments described above, the rotation rates of the hydraulic motors 3 and 3A are adjusted through pressure adjustment or by switching speed reduction ratios, crawling speed may be achieved by using a mechanical winch and adjusting its braking force, as disclosed in Japanese Patent Publication No. 3(1991)-80216. Moreover, in a controller that employs a hydraulic winch, a crawling speed may be achieved by adjusting the mechanical braking force.
Furthermore, in the embodiments described above, the true hoisting load is calculated based upon the boom derricking force and the boom angle and the excavating load is determined by subtracting the tare weight of the excavator 10 of the known art from the true hoisting load. Therefore, if a part of or the entirety of the tare weight of the excavator 10 is supported by the wall being excavated, there is a likelihood that the excavating load being detected to an excessive degree resulting in control being implemented whereby the descending speed is reduced despite the fact that the true excavating load is small. To counter this likelihood and to improve the reliability of excavating load control, the apparatus may be structured in such a manner that the load status of a power source that imparts the drive force to the excavating bit of the excavator 10 is detected so that the detected value can be compared to an upper limit value for the excavating load. If a hydraulic motor is used as the power source, the excavating load can be detected based upon the pressure of the hydraulic motor, whereas if an electric motor is employed as the power source, the excavating load can be detected based upon the current value.
In addition, while, in the first embodiment, when the speed is to be increased, the electromagnetic proportional valve 34 is closed and the electromagnetic proportional valve 31 is opened in correspondence to the quantity of speed increase and when the speed is to be reduced, the electromagnetic proportional valve 31 is closed and the electromagnetic proportional valve 34 is opened in correspondence to the quantity of speed reduction, with the operation of these valves corresponding to the level of the command signal Nw or Nv, control may be implemented in the following manner. Namely, if the desired crawling speed cannot be achieved due to insufficient leak from the existing circuits, the problem can be dealt with by opening the electromagnetic proportional valve 31 to a specific quantity in advance. In that case, speed reduction may be achieved by constricting the opening of the electromagnetic proportional valve 31 when the command signal Nw or Nv indicates a speed reduction instruction with the electromagnetic proportional valve 34 opened when the output of the speed reduction instruction is sustained even after the electromagnetic proportional valve 31 is completely closed. Or, in a case that is the reverse of the above, if the desired crawling speed cannot be achieved due to excessive leak from the existing circuits, the problem can be dealt with by opening the electromagnetic proportional valve 34 to a specific quantity in advance. In that case, the opening quantity of the electromagnetic proportional valve 34 may be constricted to increase the speed when the command signal Nw or Nv indicates a speed increase instruction with the electromagnetic proportional valve 31 opened if the output of the speed increase instruction is sustained even after the electromagnetic proportional valve 34 is completely closed.

Industrial Applicability

The controller for excavators according to the present invention may be adopted in a winch of an excavator for controlling the penetration force (excavating load) and the penetrating speed (descending speed) of the excavator to attain predetermined levels, as in the continuous wall method or in the earth drill excavation method.

Claims

A controller for excavators comprising:
a winch that causes an excavator to ascend and descend;

a penetration force detection means that detects penetration force of said excavator;

a penetration force control means that controls said winch such that said penetration force detected by said penetration force detection means attains a predetermined level of penetration force;

a descending speed detection means that detects a descending speed of said excavator;

a descending speed control means that controls said winch such that said descending speed detected by said descending speed detection means attains a predetermined level of descending speed; and

a selection means that implements a shift to control performed by said descending speed control means when a detected value of said descending speed exceeds a specific value during control performed by said penetration force control means ; wherein:
said descending speed control means controls said descending speed through proportional integration control and said penetration force control means controls said penetration force through proportional differentiation control.
A controller for excavators according to claim 1, wherein:
said penetration force detection means is constituted of an excavating load detection means that detects a true value of an excavating load imposed upon said excavator when excavating soil as said penetration force.
A controller for excavators according to claim 1, wherein:
said selection means implements a shift to control performed by said descending speed control means when said detected value of said descending speed exceeds a first specific value during control performed by said penetration force control means and implements a shift to control performed by said penetration force control means when, at least, said detected value of said descending speed is at or less than a second specific value which is smaller than said first specific value.
A controller for excavators according to claim 1, wherein:
said selection means switches to speed control performed by said descending speed control means when a detected value of said penetration force is at or less than a first specific penetration force value, switches to penetration force control performed by said penetration force control means when said detected value of said penetration force exceeds said first specific penetration force value during said speed control, implements a shift to control performed by said descending speed control means when said detected value of said descending speed exceeds a first specific speed value during said penetration force control and implements a shift to control performed by said penetration force control means when said detected value of said descending speed is at or less than a second specific speed value which is smaller than said first specific speed value and said detected value of said penetration force is at or more than a second specific penetration force value which is larger than said first specific penetration force value.
A controller for excavators comprising:
a hydraulic source that discharges pressure oil;

a hydraulic motor for winch that is connected to said hydraulic source via a first oil passage and a second oil passage;

a control valve that is provided in the middle of said first oil passage and said second oil passage;

a counter balance valve that is provided in said second oil passage which is a return side when said excavator is being lowered;

a pressure adjustment means that adjusts pressure in said second oil passage between said counter balance valve and said hydraulic motor;

a penetration force detection means that detects a penetration force of an excavator;

a penetration force control means that controls said pressure adjustment means such that a difference between said penetration force detected by said penetration force detection means and a predetermined level of penetration force becomes zero;

a descending speed detection means that detects a descending speed of said excavator;

a descending speed control means that controls said pressure adjustment means such that a difference between said descending speed detected by said descending speed detection means and a predetermined level of descending speed becomes zero; and

a selection means that implements a shift to control performed by said descending speed control means when said detected value of said descending speed exceeds a specific value during control performed by said penetration force control means.
A controller for excavators according to claim 5, wherein:
said penetration force detection means is constituted of an excavating load detection means that detects a true value of an excavating load imposed upon said excavator when excavating soil as said penetration force.
A controller for excavators according to claim 5, wherein:
said selection means implements a shift to control performed by said descending speed control means when said detected value of said descending speed exceeds a first specific value during control performed by said penetration force control means and implements a shift to control performed by said penetration force control means when, at least, said detected value of said descending speed is at or less than a second specific value which is smaller than said first specific value.
A controller for excavators according to claim 5, wherein:
said selection means switches to speed control performed by said descending speed control means when a detected value of said penetration force is at or less than a first specific penetration force value, switches to penetration force control performed by said penetration force control means when said detected value of said penetration force exceeds said first specific penetration force value during said speed control, implements a shift to control performed by said descending speed control means when said detected value of said descending speed exceeds a first specific speed value during said penetration force control and implements a shift to control performed by said penetration force control means when said detected value of said descending speed is at or less than a second specific speed value which is smaller than said first specific speed value and said detected value of said penetration force is at or more than a second specific penetration force value which is larger than said first specific penetration force value.
A controller for excavators comprising:
a hydraulic source that discharges pressure oil;

a hydraulic motor for an winch that is connected to said hydraulic source via a first oil passage and a second oil passage;

a control valve that is provided in the middle of said first oil passage and said second oil passage;

a counter balance valve that is provided in said second oil passage which is a return side when said excavator is being lowered;

a pressure adjustment means that adjusts pressure in said second oil passage between said counter balance valve and said hydraulic motor;

a penetration force detection means that detects a penetration force of said excavator;

a penetration force control means that controls said pressure adjustment means such that a difference between said penetration force detected by said penetration force detection means and a predetermined level of penetration force becomes zero;

a descending speed detection means that detects a descending speed of said excavator;

a descending speed control means that controls said pressure adjustment means such that a difference between said descending speed detected by said descending speed detection means and a predetermined level of descending speed becomes zero; and

a selection means that implements a shift to control performed by said descending speed control means when said detected value of said descending speed exceeds a specific value during control performed by said penetration force control means; wherein:
said descending speed control means controls said descending speed through proportional integration control and said penetration force control means controls said penetration force through proportional differentiation control.
A controller for excavators according to claim 9, wherein:
said penetration force detection means is constituted of an excavating load detection means that detects a true value of an excavating load imposed upon said excavator when excavating soil as said penetration force.
A controller for excavators according to claim 9, wherein:
said selection means implements a shift to control performed by said descending speed control means when said detected value of said descending speed exceeds a first specific value during control performed by said penetration force control means and implements a shift to control performed by said penetration force control means when, at least, said detected value of said descending speed is at or less than a second specific value which is smaller than said first specific value.
A controller for excavators according to claim 9, wherein:
said selection means switches to speed control performed by said descending speed control means when a detected value of said penetration force is at or less than a first specific penetration force value, switches to penetration force control performed by said penetration force control means when said detected value of said penetration force exceeds said first specific penetration force value during said speed control, implements a shift to control performed by said descending speed control means when said detected value of said descending speed exceeds a first specific speed value during said penetration force control and implements a shift to control performed by said penetration force control means when said detected value of said descending speed is at or less than a second specific speed value which is smaller than said first specific speed value and said detected value of said penetration force is at or more than a second specific penetration force value which is larger than said first specific penetration force value.
A controller for excavators comprising:
a winch that causes an excavator to ascend and descend;

a penetration force detection means that detects penetration force of said excavator;

a penetration force control means that controls said winch such that said penetration force detected by said penetration force detection means attains a predetermined level of penetration force;

a descending speed detection means that detects a descending speed of said excavator;

a descending speed control means that controls said winch such that said descending speed detected by said descending speed detection means attains a predetermined level of descending speed; and

a selection means that implements a shift to control performed by said descending speed control means when a detected value of said descending speed exceeds a first specific value during control performed by said penetration force control means and implements a shift to control performed by said penetration force control means when, at least, said detected value of said descending speed is at or less than a second specific value which is smaller than said first specific value.
A controller for excavators according to claim 13, wherein:
said penetration force detection means is constituted of an excavating load detection means that detects a true value of an excavating load imposed upon said excavator when excavating soil as said penetration force.
A controller for excavators, comprising:
a winch that causes an excavator to ascend and descend;

an excavating load detection means that detects a true value of an excavating load imposed upon said excavator when excavating soil;

an excavating load control means that controls said winch such that said excavating load detected by said excavating load detection means attains a predetermined level of excavating load;

a descending speed detection means that detects a descending speed of said excavator;

a descending speed control means that controls said winch such that said descending speed detected by said descending speed detection means attains a predetermined level of descending speed; and

a selection means that implements a shift to control performed by said descending speed control means when a detected value of said descending speed exceeds a specific value during control performed by said excavating load control means.
A controller for excavators, comprising:
a winch that causes an excavator to ascend and descend;

an excavating load detection means that detects a true value of an excavating load imposed upon said excavator when excavating soil;

an excavating load control means that controls said winch such that said excavating load detected by said excavating load detection means attains a predetermined level of excavating load;

a descending speed detection means that detects a descending speed of said excavator;

a descending speed control means that controls said winch such that said descending speed detected by said descending speed detection means attains a predetermined level of descending speed; and

a selection means that switches to speed control performed by said descending speed control means when a detected value of said penetration force is at or less than a first specific penetration force value, switches to penetration force control performed by said penetration force control means when said detected value of said penetration force exceeds said first specific penetration force value during said speed control, implements a shift to control performed by said descending speed control means when said detected value of said descending speed exceeds a first specific speed value during said penetration force control and implements a shift to control performed by said penetration force control means when said detected value of said descending speed is at or less than a second specific speed value which is smaller than said first specific speed value and said detected value of said penetration force is at or more than a second specific penetration force value which is larger than said first specific penetration force value.