JPH02198746A - Measuring device for axial tension - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention is applied to an axial force measuring device, and measures the force in a linear direction (hereinafter referred to as axial force) due to a moving body such as a spindle or table in a machine tool, for example. This invention relates to an axial force measuring device.

(Prior art) Conventionally, this type of axial force measurement has been carried out, for example, in machine tools.
It is necessary to prevent damage or breakage of tools, workpieces, and other machine tool components. And in the conventional axial force measuring device.

For example, in order to measure the axial force on a moving body such as the main shaft or table of a machine tool, it was common to attach a sensor such as a strain gauge to these moving bodies and measure the axial force based on the output signal of this sensor. .

(Problem to be Solved by the Invention) However, in conventional axial force measuring devices, forces other than the axial force to be measured are added as disturbances by drive sources such as the spindle motor and feed motor, and power transmission mechanisms such as gears. There was a problem in that the desired axial force could not be accurately measured. Furthermore, a rotary body has the disadvantage that signal transmission from it becomes extremely difficult.

Furthermore, as a means of determining the axial force 8I other than the above, there is also a method of using a 6-component force table using a piezo element or a strain gauge.
As is well known by Oiki et al., this 6-component force table is generally suitable for small to medium loads and is not suitable for measuring axial force under large loads. Furthermore, axial force measurement using a 6-component force table needs to be carried out separately and independently from the machining operation of the machine tool, which requires time and effort to install this 6-component force table on the machine tool, and it is difficult to measure the axial force in parallel during machining. There was a problem in that it was not possible to measure the axial force and use the measurement results to change the machining conditions.

The present invention was proposed to solve the above-mentioned problems, and its purpose is to accurately measure the axial force of a linearly moving body without being affected by disturbances, etc., and to To provide an axial force measuring device with a simple configuration, which eliminates the trouble of installation by pre-fabricating a load cell into a machine tool or the like, and which enables constant axial force 8+11 in parallel with machining operation.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a load cell in a system that is substantially stationary relative to the linear motion direction of a moving body such as a spindle head or a table of a machine tool. The present invention is characterized in that the force when the moving body moves linearly is measured by the load cell.

In addition, the axial force measuring device according to the present invention is planned to be mainly applied to machine tools, and in that case, the moving body is the main shaft of the machine tool, and a collar that presses a bearing attached to the main shaft is used. It is preferable to provide a load cell in the nut of the ball screw that moves the moving body such as a table or a spindle head.

Furthermore, when a force exceeding a set value is applied to a moving object such as a table or spindle head, it is detected that the mover has moved by a certain amount of displacement along the direction of this force, and the movement of the moving object is stopped. The structure was designed to allow the pilot to evacuate to the safe side. The present invention can also be applied to the fail-safe system disclosed in Japanese Patent Application No. 63-206054, and in that case, it is desirable to include a load cell in the actuator that is equipped with the movable element and responds to the force from the moving body. .

(Function) According to the present invention, the axial force of a linearly moving moving body is applied to a system that is substantially stationary relative to this moving body, and the load cell provided in this system responds to the axial force. generates an electrical signal. Therefore, by measuring this electrical signal, the axial force of the moving body can be measured.

(Example) The present invention will be described in detail below with reference to the drawings.

First of all, FIGS. 1 to 5 show a first embodiment of the present invention, and this embodiment incorporates the axial force measuring device according to the present invention into the housing of the main shaft bearing of a machine tool such as a machining center. It is something.

In FIG. 1, reference numeral 1 denotes a main shaft as a moving body that moves linearly, and a plurality of bearings 2 are mounted on the main shaft 1 along its axial direction. Between these bearings 2, there are an inner ring collar 3 and an outer ring collar 4 of the bearing 2.
5 are appropriately arranged. Also, the top bearing 2
An axially long inner ring collar 6 is disposed between the inner ring 2A and the head IA of the main shaft 1.

Furthermore, 7 is a housing that accommodates the bearing 2 and each of the collars 3 to 6. An outer ring holder 8 is provided inside the upper end of the housing 7, and the outer ring holder 8 is attached to the upper end of the housing 7 by a bolt 9. Tightening is possible.

On the other hand, a ring-shaped axial force sensor collar 10 constituting a load cell is attached between the outer ring holder 8 and the outer ring holder 8 of the uppermost bearing 2. This axial force sensor collar 10 is given a preload in the direction of pressing the uppermost bearing 2 by tightening the outer ring holder 8.
Its configuration is as shown in FIG. That is, a wide groove 12 is formed in the center of the outer peripheral surface of the ring-shaped main body 11.

A narrow groove 13 is formed in the center of the inner peripheral surface of the main body 11, and strain gauges 14 are fixed to each of the grooves 12 at positions that divide the outer peripheral surface thereof into four quarters.

Inside the groove 12 to which the strain gauge 14 is fixed,
Silicone rubber 16 is filled to protect the strain gauge 14.

Here, FIG. 3 is an enlarged view of section a in FIG. 2. To describe an example of the dimensional relationship of each part based on the same figure, the axial force sensor collar up to the bottom of the groove 12 will now be described.
When the diameter D of groove 1 (see Figure 2) is 80 m, groove 1
The width L8 of the grooves 12 and 13 is 4 to 5 mm, the width L2 of the grooves 13 is 1 m, and the thickness d of the thin portion 15 between these grooves 12 and 13 is 0.5++n.

The axial force sensor collar 10 moves linearly as a component of the spindle head together with the main shaft 1, which is a moving body, but it is a system that is almost stationary in the axial direction with respect to the main shaft 1. It consists of

Therefore, the relationship between the main shaft 1 and the bearing 2 shown in FIG. 1 can be considered as a spring system model as shown in FIG. 4. That is, when a force is applied to the main shaft 1 along its axial direction in FIG. 1, the bearing 2 is elastically deformed. to each,, to 2
) can be replaced by On the other hand, the fourth
In the figure, 101 is a main shaft as a moving body, and 301 is a substantially stationary system such as outer ring collars 4 and 5 and outer ring retainer 8 shown in FIG.

In such a model, a force f is initially applied to the main shaft 101.
0 is applied, and in this state, assume that an axial force fex is applied from the outside in the direction of the arrow in FIG.

This axial force fex is shared by the springs 201 and 202 as mutually opposite forces Δf1 and Δf2, respectively, as shown in FIG. 5, and the spring 201 has a displacement ΔX according to a displacement characteristic line arise. On the other hand, the spring 202 produces the same displacement ΔX according to the displacement characteristic line x2 whose spring constant is 2.

In other words, 5-axis force fax, spring constant 0. , and the displacement Δ
Between X.

fax=Δf1+Δf, =, Δx+, ΔX=(k1
There is a relationship called ΔX.

Here, assuming that the spring constants are known, the axial force fex can be calculated by finding the displacement ΔX of the springs 201 and 202. As is clear from FIG. 4, this displacement ΔX can be detected from the substantially stationary system 301 side.

In the above model, measuring the displacement ΔX from the substantially stationary system 301 side means that in the embodiment shown in FIG.
This corresponds to measuring the strain due to the axial force sensor color from a substantially stationary system.
By detecting the strain caused by the bearing 2 at the position 10, it becomes possible to measure the axial force of the main shaft 1.

That is, in FIG. 1, a preload is applied to the axial force sensor collar 10 by the outer ring presser 8 as described above.

In this state, the axial force of the main shaft 1 is transmitted from the inner ring collar 6 to the inner ring 2A of the uppermost bearing 2, and then part of the axial force is transferred from the inner ring 2A of the next-stage bearing 2 to the inner ring collar 3 to the next-stage bearing. The signal is transmitted through the route from the inner ring 2A of 2 to... Also.

The remainder of the axial force transmitted to the inner ring 2A of the top bearing 2 is the ball of the bearing 2 - the outer ring 2B of the bearing 2 →
It is transmitted along the path of the outer ring 2B of the next stage bearing 2 → the outer shaft collar 4 → the outer ring 2B of the next stage bearing 2 →...

Therefore, the reaction force of the force applied to the outer ring 2B is applied to the axial force sensor collar 1O, which is constantly pressed against the outer ring 2B of the uppermost bearing 2, and the above-mentioned thin wall portion 15 is distorted, thereby causing the axis of the main shaft 1. An electrical signal proportional to the force can be obtained from the strain gauge 14.

Incidentally, if the axial force sensor collar 10 is arranged directly under the outer ring retainer 8 as in the above embodiment, there is an advantage that the output electric signal of the strain gauge 14 can be easily taken out from the outside of the inner ring collar 6. The position of the sensor collar 10 is not limited to this in any way, and may be in the position of the outer ring collars 4, 5, etc. in FIG. 1 as long as it does not interfere with the extraction of electrical signals.

Next, FIGS. 6 and 7 show a second embodiment of the present invention, in which the axial force measuring device according to the present invention is
It is installed in the nut section attached to the ball screws of each of the x, y, and z axes of the machining center. For example, in FIG. 6, the table 30 as a moving body that moves linearly is
This is an example in which the present invention is applied to a nut portion of a ball screw 40 for moving along an axis. In this case as well, the nut portion 20 constitutes a system that is substantially stationary relative to the direction of linear movement of the table 30.

That is, in the figure, the nut portion 20 screwed onto the ball screw 40 is integrally fixed to the arm 31 protruding from the table 30 by the nut 21.

The nut portion 20 has a wide groove 22 formed at the center of its outer circumference, and a narrow groove 23 formed at the center of its inner circumference. Strain gauges 24 are fixed at each of the quarter positions. Furthermore, as is clear from Fig. 7, which is an enlarged view of part b in Fig. 6,
A thin wall portion 25 is formed between the groove 22 and the groove 23. Moreover, inside the groove 22 to which the strain gauge 24 is fixed,
It is filled with silicone rubber 26 having low foamability or elasticity and oil-resistant silicone rubber 27. In FIG. 7, for example, the thickness d of the thin portion 25 is 0.5 mm, and the groove 2
3, l1lITL2 is 1+w+, and a corner portion 23a of the groove 23 is formed in a rounded shape with a radius of 0.2 mm.

As described above, in this embodiment, the nut portion 20 itself constitutes a load cell, and this load cell measures the axial force of the table 30 in the X-axis direction in the following manner. That is, in FIG. 6, the nut portion 20 moves along the ball screw 40 due to the rotation of the ball screw 40,
Along with this, the table 30 will move in the X-axis direction via the arm 31, but assuming that there is no loss of force between the nut portion 20 and the arm 31 at this time, the table 30 will move in the X-axis direction. The force can be measured by the load cell in the nut part 20. That is, the thin wall portion 25 of the load cell shown in FIG. 7 is distorted due to the reaction force from the arm 31 of the table 30 that the nut portion 20 receives.

An electric signal proportional to the reaction force, in other words, the axial force of the table 30 in the X-axis direction can be obtained from the strain gauge 24,
As in the first embodiment, axial force can be measured from a substantially stationary system.

Next, FIGS. 8 and 9 show a third embodiment of the present invention. In this embodiment, an axial force measuring device according to the present invention is applied to an actuator of a machining center incorporating a fail-safe system. This fail-safe system and actuator have already been proposed by the inventor in Japanese Patent Application No. 63-206054,
The outline will be explained below.

This fail-safe system is capable of
A mover that moves along the direction of this force, a stopper that sets the initial position of this mover, and a force such as a hydraulic mechanism that supports the mover and applies a preset constant force to the mover. The system is equipped with a working body, and detects that the movable element has moved by a certain amount in response to a force from the movable body, stops the movement of the movable body, and evacuates the system to a safe side.

In addition, the actuator is a component of this fail-safe system and responds to the force from the moving object, and when a force greater than a set value is applied from the moving object, it moves along the direction of this force. and a stopper for setting the initial position of the slider, and the slider is supported by a force applying body provided inside or outside to apply a preset constant force to the slider. be.

For example, FIG. 8 shows a machining center incorporating a fail-safe system that uses hydraulic pressure as a force applying body. In the figure, 51 is a column, 52 is a spindle head as a moving body, and 53 is attached to a tool holder 54. 56 is a workpiece; 30 is a table as a moving body as described above; 57 is a base;
8 is a saddle, and 40 is a ball screw 20A for moving the table 30 in the X-axis direction, which is a nut screwed onto the ball screw 40.

Further, 59 is an actuator which is similar in principle to a hydraulic cylinder, and this actuator 59 is connected between the table 30 and the oak 1 part 20A, between the spindle head 52 and a ball screw 60 that moves the spindle head 52 in the Z direction. between the nut part 61, and further between the base 57 and the saddle 58.
A ball screw is also provided between the The hydraulic pressure from these actuators 59 is all 1
It is connected to an accumulator 62 provided outside. A hydraulic motor 63 is attached to this accumulator 62, and the rotational position of the hydraulic motor 63 is set to N.
By changing the operating point of the actuator 59, that is, the setting value of the force applied to the table 30 and the spindle head 52, by changing the C program, for example, loOkgf, 500kgf,
It can be changed to 100100O.

Next, an example of a specific configuration of the actuator 59 is shown in FIG. In addition, in FIG. 9, the table 30 and the nut part 2
Although the actuator 59 provided between 0A and 0A is shown, the basic configuration is the same for actuators provided in other parts.

In the figure, 64 is a cylinder with a hollow structure to which the ball screw 40 is screwed, and 65 is a cylinder with a hollow structure arranged concentrically with the cylinder 64. Nut part 20
The arm 31 of the table 30 is integrally connected to the end of the cylinder 65.

Here, the cylinders 64 and 65 are the table 3 which is a moving body.
0, it acts as a mover in a fail-safe system.

A piston 66 with a hollow structure is provided in the cylinder 64.65, and the piston 66 and the cylinder 64.
5 is filled with oil as shown in the figure.

This oil then reaches an external accumulator 62 shown in FIG. Further, 67 is an arm made of a magnetic material connected to the piston 66, and an inductive proximity switch 68 with a built-in coil that is indirectly fixed to the cylinders 64 and 65 is arranged to face the arm 67. There is.

In this actuator 59, the ball screw 4
0 rotation applies force to the table 30 via the cylinder 65, and when the reaction force exceeds the set value by the accumulator 62, the failsafe system operates and the piston 66 moves relatively to the left in the figure. This increases the distance between the arm 67 made of magnetic material and the inductive proximity switch 68.

The fact that a force exceeding a set value is applied to the table 30 as a moving body can be outputted as an electric signal from the inductive proximity switch 68.

In the actuator 59, the cylinder 65 is substantially stationary relative to the linearly moving table 30, and one cylinder 65 is located at substantially the same position as the nut portion 20 in FIGS. 6 and 7 for axial force measurement according to the present invention. It is possible to build a load cell into the device. That is, as shown in FIG. 9, a wide groove 72 is formed in the center of the outer peripheral surface of the cylinder 65,
Further, a narrow groove 73 is formed in the center of the inner peripheral surface.

Strain gauges 74 are fixed to the bottoms of the grooves 72 at positions that divide the outer circumferential surface into quarters, and the insides of the grooves 72 are filled with silicone rubber 76 having low foamability or elasticity and oil-resistant silicone rubber 77. There is. Furthermore, groove 72 and groove 7
A thin wall portion 75 is formed between the load cell and the load cell.

Also in this embodiment, the X of the table 30 moving linearly is
The thin wall portion 75 of the load cell is distorted in response to the axial force, and an electric signal proportional to the axial force can be obtained from the strain gauge 74, making it possible to measure the axial force of the table 30 from a substantially stationary system. In particular, in this embodiment, based on the axial force thus measured, the force set value by the aforementioned accumulator 62, that is, the force set value at which the fail-safe system operates can be changed in real time, and the optimum operating set value is always maintained. A fail-safe system can be realized.

Further, in this embodiment, the load cell can also be provided at the C section of the piston 66 or the D section of the cylinder 64 in FIG.

Note that the present invention is not limited to the above-mentioned embodiments, but can be applied to measuring the axial force of various moving bodies that move linearly. Further, the present invention can be applied to a system that measures the axial force of a machine such as a machine tool and adaptively controls the feed, rotation, etc. of a moving body in real time.

(Effects of the Invention) As described above, according to the present invention, since the axial force of a linearly moving moving body is detected by a load cell installed in a substantially stationary system, the motor, etc., present on the moving body side can be activated. The axial force of a moving body can be accurately measured without being affected by disturbances due to the movement of power transmission mechanisms such as power sources and gears.

Also, since the structure of the load cell itself is extremely simple,
The axial force measuring device according to the present invention can be provided at low cost.

Furthermore, this load cell can be built in advance into the main spindle bearing housing of a machine tool or the nut of a ball screw, making it possible to use a 6-minute table etc. each time to measure the axial force, as in the past. You can eliminate the hassle of installation.

It is also possible to measure axial force under large loads. at the same time.

Since the axial force can be measured in parallel with the machining operation of the machine tool, machining conditions etc. can be quickly changed according to the measured axial force, realizing a highly efficient and highly accurate machining system. Can be done.

In addition, by using the present invention, it is possible to accumulate data on the force of a moving body under certain processing conditions, and by analyzing this data using an NG computer, etc., it is possible to predict tool life, damage, breakage, etc. can be done. That is,
By using this accumulated data, the machine tool itself can automatically select and set the optimal machining conditions, making it possible to equip the machine tool with a so-called self-learning function.

[Brief explanation of the drawing]

Figures 1 to 5 show a first embodiment of the present invention, in which Figure 1 is an explanatory diagram of the main part, Figure 2 is an explanatory diagram of the axial force sensor collar, and Figure 3 is a diagram of the a in Figure 2. FIG. 4 is a model diagram of a spring system isometrically similar to this embodiment, and FIG. 5 is a diagram showing its Kerr displacement characteristics. 6 and 7 show a second embodiment of the present invention,
FIG. 6 is an explanatory diagram of the main part, FIG. 7 is an enlarged explanatory diagram of part b in FIG. 6, FIGS. 8 and 9 show a third embodiment of the present invention, and FIG. Configuration diagram, No. 9
The figure is a sectional view of the actuator. fs6 Fig. 1... Main shaft 10... Axial force sensor collar 12, 13, 22, 23, 72, 73... Groove 14.2
4.74...Strain gauge 20, 2OA...Nut part 40...Ball screw 64.65...Cylinder 7...Housing 15.25.75...Thin wall part 30...Table 59 ...Actuator Figure 7

Claims (4)

[Claims] (1) An axial force measuring device characterized in that it receives a force from a linearly moving moving body and measures the force from the moving body using a load cell. (2) The axial force measuring device according to claim 1, wherein the moving body is a main shaft of a machine tool, and the load cell is provided on a collar that is pressed into contact with a bearing attached to the main shaft. (3) The axial force measuring device according to claim (1), wherein a load cell is provided in a nut portion of a ball screw for driving a moving body in a machine tool. (4) When a force exceeding a set value is applied to a moving body in a machine tool, it is detected that the mover has moved by a certain amount of displacement along the direction of this force, and the movement of the moving body is stopped. Claim 1: In the safe system, a load cell is provided in the actuator provided with the mover.
) Axial force measuring device described.