CN109894906B - Redundant drive parallel machine tool dead point avoidance system and method - Google Patents

Abstract

The invention discloses a system and method for avoiding dead point of a redundant drive parallel machine tool. The system comprises a tachometer generator and a photoelectric encoder connected with the servo motors of three retractable rod groups; a linear induction synchronizer connected with the redundant sliding block , and the dead point monitoring processor; the tachogenerator is used to collect the output speed of the servo motors of the three telescopic rod groups; the photoelectric encoder is used to collect the number of turns of the lead screws of the three telescopic rod groups; the linear induction synchronizer is used for The position of the redundant slider on its guide rail is collected; the dead point monitoring processor is used to determine whether the parallel mechanism is close to the dead point position, and controls the expansion and contraction of the three telescopic rod groups and the movement direction of the redundant slider to avoid the dead point position; the method includes obtaining The output speed of the three telescopic rod groups, the number of turns of the lead screw, the coordinates of the redundant slider on the guide rail; calculate the speed of the moving platform; determine whether it is close to the dead center position; control the movement of each telescopic rod group and the redundant slider Avoid dead spots. The present invention can predict dead spots and avoid dead spots.

Description

A system and method for avoiding dead point of redundant drive parallel machine tool

technical field

The invention belongs to the field of parallel machine tool motion control, in particular to a system and method for avoiding dead point of a redundant drive parallel machine tool.

Background technique

Since the Stewart mechanism was proposed in the 1960s, the parallel mechanism has been widely used due to its high precision, good dynamic response, and large stiffness-to-weight ratio. As the result of the combination of parallel mechanism and machine tool technology, the parallel machine tool is a highly efficient modern cutting equipment, so the research on the parallel mechanism applied to the parallel machine tool is more and more important. However, the parallel mechanism has the same dead point position as the traditional mechanism, and due to the complex movement of the parallel mechanism, the driving rods cooperate with each other and restrict each other, so it is more difficult to accurately predict and avoid the dead point position in the motion space. The existence of the dead point of the mechanism has a great influence on the normal operation of the mechanism, so it is particularly important to accurately and efficiently predict the dead point position and avoid the dead point position. Du Ye. Numerical control research on a C-shaped gantry parallel machine tool with two redundant drives [D]. Nanjing: Nanjing University of Science and Technology, 2017 A dead-point analysis of the parallel mechanism in a C-shaped gantry parallel machine tool is disclosed, but there is no The specific dead point monitoring and avoidance methods are given.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a system and method for avoiding the dead point of a redundant driving parallel machine tool, so as to solve the problem of accurately predicting and avoiding the dead point of the redundant driving parallel machine tool.

The technical solution that realizes the object of the present invention is:

A redundant drive parallel machine tool dead point avoidance system, comprising three tachometer generators respectively connected with the servo motors of the upper telescopic rod group, the middle telescopic rod group and the lower telescopic rod group, respectively connected to the upper telescopic rod group and the middle telescopic rod group The three electric encoders connected with the lead screw of the lower telescopic rod group, the linear induction synchronizer connected with the redundant slider, and the dead point monitoring processor;

The three tachometer generators are respectively used to collect the output rotational speed of the servo motors in the upper telescopic rod group, the middle telescopic rod group and the lower telescopic rod group; the three photoelectric encoders are used to collect the upper telescopic rod group, the middle The number of turns of the lead screw in the telescopic rod group and the lower telescopic rod group; the linear induction synchronizer is used to collect the position of the redundant slider on its guide rail; the dead point monitoring processor is used to calculate the speed of the moving platform And the ratio of the speed of the telescopic rod group, and compare the ratio with the dead point setting value, and determine whether the parallel mechanism is close to the dead point position, according to the judgment result, control the expansion and contraction of the three telescopic rod groups and the movement direction of the redundant slider to Avoid dead spots.

A method for redundantly driving a dead point avoidance system of a parallel machine tool, comprising the following steps:

Step 1. Obtain the output speeds n ₁ , n ₂ , n ₃ of the servo motors in the upper telescopic rod group, the middle telescopic rod group and the lower telescopic rod group; The number of turns a ₁ , a ₂ , a ₃ of the lead screw; the position of the redundant slider on its guide rail to determine the coordinates of the redundant slider on the guide rail;

Step 2: Calculate the telescopic speeds v ₁ , v ₂ , v ₃ of the upper telescopic rod group, the middle telescopic rod group and the lower telescopic rod group respectively; calculate the rods of the upper telescopic rod group, the middle telescopic rod group and the lower telescopic rod group respectively length l ₁ , l ₂ , l ₃ ;

Step 3. Calculate the speed of the moving platform: the speed v ₁ , v ₂ , v ₃ and the lengths l ₁ , l ₂ , and l ₃ of each telescopic rod have been obtained, and the moving speed v _d of the moving platform is obtained through the speed Jacobian matrix; The non-zero telescopic rod speed and the moving platform speed are modulo;

Step 4. Determine whether the mechanism is close to the dead center position: calculate the ratio between the moving speed value of the moving platform and the telescopic speed value of each telescopic rod, and compare the obtained ratio with the dead center setting value S in the data setting module; if If any ratio is greater than the set value, it means that the mechanism is close to the dead point; if the ratio is not greater than the set value, it means that the mechanism is not close to the dead point;

Step 5. Control the movement of each telescopic rod group and the redundant slider to avoid the dead center position.

Compared with the prior art, the present invention has the following significant advantages:

(1) The system of the present invention can determine whether the parallel mechanism is close to the dead center position by collecting the output speed of the motors of the three telescopic rods, the number of turns of the lead screw, and the position of the redundant slider on its guide rail. As a result, the three telescopic rod groups can be controlled to extend and retract and the moving direction of the redundant slider to avoid the dead center position.

(2) The dead point approaching determination method adopted in the present invention is fast, fast in calculation speed, and good in real-time performance, which can meet the high requirements of machine tools for real-time performance.

(3) The data required by the present invention is easy to collect, the collection method is simple, and the processing of the data is easy to realize, the determination of the proximity of the dead point is accurate, and the position of the dead point can be completely avoided.

(4) The present invention adopts the user input dead point setting value, and the user can input different dead point setting values according to the structural parameters of the parallel mechanism and different requirements for the closeness of the dead point.

Description of drawings

FIG. 1 is a schematic structural diagram of the system and method for avoiding dead point of a redundant drive parallel machine tool according to the present invention.

FIG. 2 is a flow chart of the system and method for driving a parallel machine tool dead point avoidance according to the present invention.

FIG. 3 is a schematic diagram of the parallel mechanism in the redundant drive parallel machine tool of the present invention.

FIG. 4 is a simplified mechanism diagram of the parallel mechanism in the redundant drive parallel machine tool of the present invention.

Detailed ways

The present invention will be further introduced below with reference to the accompanying drawings and specific embodiments.

Referring to Figure 2, a parallel mechanism in a redundant drive parallel machine tool includes an upper telescopic rod group, a lower telescopic rod group, a middle telescopic rod group, redundant sliders and guide rails, and four servo motors; one end of the upper telescopic rod group is It is fixed by a ball hinge, and the other end is connected with the upper part of the moving platform by a ball hinge; one end of the lower telescopic rod group is fixed by a ball hinge, and the other end is connected with the bottom of the moving platform by a ball hinge; one end of the middle telescopic rod group is connected with a ball hinge at one end. The redundant sliders are connected, and the other end is connected with the back of the moving platform by a ball joint; each telescopic rod group is connected with a servo motor, and the servo motor drives the lead screws in the two telescopic rods synchronously, so that the two telescopic rods do the same Telescopic movement; the redundant slider guide is fixed, and the redundant slider can move freely on the guide rail; the redundant slider is driven by a servo motor; each telescopic rod is composed of two telescopic rod groups with the same structure, In addition, the two telescopic rods in each telescopic rod group are always guaranteed to be parallel and of equal length, so the parallel structure can be simplified as the mechanism shown in FIG. 4 .

1, a redundant drive parallel machine tool dead center avoidance system of the present invention includes a first tachometer generator 1, a second tachometer connected to the servo motors of the upper telescopic rod group, the middle telescopic rod group, and the lower telescopic rod group, respectively. The tachogenerator 2, the third tachogenerator 3, the first photoelectric encoder 11, the second photoelectric encoder 12, the third photoelectric encoder 11, the second photoelectric encoder 12, the third photoelectric Encoder 13, linear inductive synchronizer connected to redundant sliders, and dead center monitoring processor.

The first tachogenerator 1, the second tachogenerator 2, and the third tachogenerator 3 are respectively used to collect the output rotational speed n ₁ , n ₂ , n ₃ ; the first photoelectric encoder 11 , the second photoelectric encoder 12 and the third photoelectric encoder 13 are respectively used to collect the lead screws in the upper telescopic rod group, the middle telescopic rod group and the lower telescopic rod group The number of turns a ₁ , a ₂ , a ₃ turned; the linear induction synchronizer is used to collect the position of the redundant slider on its guide rail; the dead point monitoring processor is used to calculate the speed of the moving platform and the three telescopic The ratio of the speed of the rod group, and compare the ratio with the dead point setting value, and determine whether the parallel mechanism is close to the dead point position. point location.

Further, the dead point monitoring processor includes a data setting module, a data acquisition module, a speed processing module, a dead point proximity determination module, and a motion control module;

The data setting module is used to set the dead point setting value S; the ratio of the telescopic speed of each telescopic rod group of the parallel mechanism to the speed of the moving platform of the parallel mechanism is calculated near the dead point of the parallel mechanism (which can be obtained by MATLAB simulation. to obtain the distribution map of the above ratios in three-dimensional space). Select a ratio as the dead point setting value according to the distance from the dead point position to the dead point that is expected to be avoided in advance. When the dead point is close to the judgment, it needs to compare with the set value input by this module to determine whether it is close to the dead point.

The data acquisition module is used to receive data from the first tachogenerator 1 , the second tachogenerator 2 , the third tachogenerator 3 , the first photoelectric encoder 11 , the second photoelectric encoder 12 , and the third photoelectric encoder 13 and the signal from the linear induction synchronizer; and receiving the signal from the linear induction synchronizer to determine the position of the redundant slider;

The speed processing module is used to obtain the telescopic speed of each telescopic rod group according to the output speed of the servo motor in each telescopic rod group measured by the tachogenerator and the transmission ratio in each telescopic rod group, and to measure the telescopic speed of each telescopic rod group according to the photoelectric encoder. The number of turns and the lead of the lead screw in each telescopic rod group can be obtained to obtain the rod length; according to the telescopic speed and rod length of each telescopic rod group, the moving speed of the moving platform can be obtained.

The dead point proximity determination module is used to calculate the ratio between the moving speed value of the moving platform and the telescopic speed value of each telescopic rod group, compare the obtained ratio with the set value in the data setting module, and determine whether the mechanism is close to dead point.

The motion control module is used to control the expansion and contraction of the three telescopic rod groups and the movement direction of the redundant sliders to avoid the dead point position according to whether the mechanism is close to the dead point: if it is close to the dead point, the upper and lower two telescopic rod groups are fixed, and the middle The telescopic rod group can be freely retracted, and the redundant sliding block moves in the forward or direction of the sliding rail according to the current position. If the mechanism is not close to the dead point, the redundant slider does not move, and the data acquisition is performed again and the calculation is performed to determine whether the mechanism is close to the dead point.

Further, the speed processing module includes a telescopic rod telescopic speed calculation unit, a telescopic rod rod length calculation unit, and a moving platform motion speed calculation unit;

The telescopic rod telescopic speed calculation unit obtains the telescopic speed of each telescopic rod group respectively according to the output speed of the servo motor in each telescopic rod group and the transmission ratio in each telescopic rod group measured by the tachometer generator;

Assume that the transmission ratios of the servo motor speed and the telescopic speed of the telescopic rods in the three telescopic rod groups are i ₁ , i ₂ , and i ₃ , respectively,

Then the telescopic speed of the upper telescopic rod group is: v ₁ =n ₁ ·i ₁ ;

The telescopic speed of the middle telescopic rod group is: v ₂ =n ₂ ·i ₂ ;

The telescopic speed of the lower telescopic rod group is: v ₃ =n ₃ ·i ₃ ;

The rod length calculation unit of the telescopic rod obtains the rod length according to the number of turns and the lead of the rotation of the lead screw in each telescopic rod group measured by the photoelectric encoder;

Let the lead screw leads in the three telescopic rod groups be L ₁ , L ₂ , and L ₃ respectively;

Then the rod length of the upper telescopic rod group is: l ₁ =a ₁ ·L ₁ ;

The rod length of the middle telescopic rod group is: l ₂ =a ₂ ·L ₂ ;

The rod length of the lower telescopic rod group is: l ₃ =a ₃ ·L ₃ ;

The moving platform moving speed calculation unit calculates the moving platform moving speed v _d through the speed of each telescopic rod group v ₁ , v ₂ , v ₃ and the rod lengths l ₁ , l ₂ , l ₃ , and then through the velocity Jacobian matrix. Delete the velocities that are 0 in the velocities v ₁ , v ₂ , and v ₃ of each telescopic rod group, and calculate the modulo of the non-zero telescopic rod group velocities and the moving platform velocities, namely |v ₁ |, |v ₂ |, |v ₃ |, |v _d |, let the speed of the telescopic rod group not be 0.

Further, the specific process of calculating the ratio of the moving speed value of the moving platform to the telescopic speed value of each telescopic rod group by the dead point proximity determination module is as follows:

Let the sliding direction of the redundant slider along the guide rail be the X axis, and the x coordinate of the redundant slider at the middle position of the guide rail is 0. According to the position of the redundant slider on the guide rail, determine its x coordinate in the machine tool coordinates. is x _s .

The dead point approach determination module calculates the ratio of the moving speed value of the moving platform and the telescopic speed value of each telescopic rod group, and compares the obtained ratio with the dead point setting value S in the data setting module. If there is any ratio greater than the set value, it means that the mechanism is close to the dead point; if the ratio is not greater than the set value, it means that the mechanism is not close to the dead point. which is:

机构未接近死点；否则，机构接近死点。like

The mechanism is not near dead center; otherwise, the mechanism is near dead center.

According to the above judgment result, if the mechanism is close to the dead point, the motion control module determines how to control the servo motor of the redundant slider according to the current position of the redundant slider, and then controls the servo motor of the upper and lower telescopic rod groups to be locked, and the middle telescopic rod group is locked. It can be freely stretched; if the redundant slider at the X-axis coordinate x _s is less than zero (coordinate x _s < 0), it will send a signal to the servo motor to control the redundant slider to move in the positive direction of the X-axis; otherwise (coordinate x _s ≥ 0), send a signal to the servo motor to control the redundant slider to move in the negative direction of the X axis.

A method for redundantly driving a dead point avoidance system of a parallel machine tool, comprising the following steps:

Step 1. Input the dead point setting value S, which can be used to avoid the dead point position according to the different requirements for the proximity of the dead point;

Step 2, obtain the output speeds n ₁ , n ₂ , n ₃ of the servo motors in the upper telescopic rod group, the middle telescopic rod group and the lower telescopic rod group; The number of turns a ₁ , a ₂ , a ₃ of the lead screw; the position of the redundant slider on its guide rail to determine the coordinates of the redundant slider on the guide rail;

Step 3. Calculate the telescopic speeds v ₁ , v ₂ , v ₃ of the upper telescopic rod group, the middle telescopic rod group and the lower telescopic rod group respectively; calculate the rod lengths of the upper telescopic rod group, the middle telescopic rod group and the lower telescopic rod group respectively l ₁ , l ₂ , l ₃ ;

According to the output speed of the servo motor in each telescopic rod group measured by the tachogenerator and the transmission ratio in each telescopic rod group, the telescopic speed of each telescopic rod group is obtained respectively; the wire in each telescopic rod group is measured according to the photoelectric encoder. The number of turns and the lead of the bar rotation are used to obtain the bar length;

3.1. Calculate the telescopic speed v ₁ , v ₂ , v ₃ of the upper telescopic rod group, the middle telescopic rod group and the lower telescopic rod group: the telescopic speed of the upper telescopic rod group is v ₁ =n ₁ ·i ₁ , the middle telescopic rod group The telescopic speed of the lower telescopic rod group is v ₂ =n ₂ ·i ₂ , and the telescopic speed of the lower telescopic rod group is v ₃ =n ₃ ·i ₃ .

3.2. Calculate the rod lengths l ₁ , l ₂ and l ₃ of the upper telescopic rod group, the middle telescopic rod group and the lower telescopic rod group: the rod length of the upper telescopic rod group is l ₁ =a ₁ ·L ₁ , the middle telescopic rod The rod length of the group is l ₂ =a ₂ ·L ₂ , and the rod length of the lower telescopic rod group is l ₃ =a ₃ ·L ₃ .

Step 4. Calculate the velocity of the moving platform: The velocity v ₁ , v ₂ , v ₃ and the lengths l ₁ , l ₂ , and l ₃ of each telescopic rod group have been obtained, and the moving velocity v _d of the moving platform is obtained through the velocity Jacobian matrix.

Delete the velocities that are 0 in the velocities v ₁ , v ₂ , and v ₃ of each telescopic rod group, and calculate the modulo of the non-zero telescopic rod group velocities and the moving platform velocities, namely |v ₁ |, |v ₂ |, |v ₃ |, |v _d |, let the speed of the telescopic rod group not be 0.

Step 5, determine whether the mechanism is close to the dead center position: calculate the ratio of the moving speed value of the moving platform and the telescopic speed value of each telescopic rod group, and compare the obtained ratio with the dead point setting value S in the data setting module; If there is any ratio greater than the set value, it means that the mechanism is close to the dead point; if the ratio is not greater than the set value, it means that the mechanism is not close to the dead point.

which is:

机构未接近死点；否则，机构接近死点。like

The mechanism is not near dead center; otherwise, the mechanism is near dead center.

Step 6. Control the movement of each telescopic rod group and the redundant slider to avoid the dead point position:

If the mechanism is close to the dead center, according to the current position of the redundant slider, determine how to control the servo motor of the redundant slider, and then control the servo motor of the upper and lower telescopic rod groups to lock, and the middle telescopic rod group can be freely retracted; if the redundant slider is in If the coordinate x _s in the X-axis coordinate is less than zero, send a signal to the servo motor to control the redundant slider to move in the positive direction of the X-axis; otherwise, send a signal to the servo motor to control the redundant slider to move in the negative direction of the X-axis direction move.

Among them, the sliding direction of the redundant slider along the guide rail is the X axis, and the x coordinate of the redundant slider at the middle position of the guide rail is 0. According to the position of the redundant slider on the guide rail, determine its x coordinate in the machine tool coordinate The coordinates are x _s .

The link structure of the present invention is simplified as Fig. 4. According to the mechanism principle of the parallel mechanism of the parallel machine tool, when the rod lengths of the upper and lower telescopic rods are both fixed values, the upper and lower branch chains can determine a circle, and the middle branch chain and the circumference The intersection is the location of the end of the mechanism. If the middle branch chain intersects with the line connecting the fixed positions of the two branch chains (C ₁ C ₂ line), the transmission angle is zero at this time, and the mechanism reaches the dead center position. According to the positional relationship of the mechanism, when the rod lengths of the upper and lower telescopic rod groups are determined, the increment of the rod length of the middle telescopic rod group has a nonlinear relationship with the moving distance of the end. Under the same increment of the rod length of the middle telescopic rod group , the closer to the dead center position, the greater the end movement distance. Therefore, the present invention only needs to measure the speed of the telescopic rod group and the speed of the end of the mechanism in real time, and determine whether the parallel mechanism is close to the dead center position by comparing the ratio between the two with the set value.

The data to be collected in the present invention is relatively easy to collect, and the collection method is simple and reliable; in data processing, the algorithm is simple and easy to implement and the judgment result is reliable; the data required for the close-to-dead-point judgment is also less and the calculation is simple, so the calculation speed is fast , the response is sensitive, which can meet the high requirements of the machine tool for real-time performance; it also adopts a data setting module, and the user can input different dead point setting values according to the structural parameters of the parallel mechanism under study and the requirements for the proximity of the dead point, so that the The parallel mechanism avoids the dead point in advance.

Claims (8)

1. a redundant drive parallel machine tool dead point avoidance system, is characterized in that, comprises three tachometer generators that are connected with the servo motors of the upper telescopic rod group, the middle telescopic rod group, the lower telescopic rod group, respectively, and the upper telescopic rod group respectively. Three photoelectric encoders connected with the lead screw of the rod group, the middle telescopic rod group and the lower telescopic rod group, the linear induction synchronizer connected with the redundant slider, and the dead point monitoring processor; The three tachometer generators are respectively used to collect the output rotational speed of the servo motors in the upper telescopic rod group, the middle telescopic rod group and the lower telescopic rod group; the three photoelectric encoders are used to collect the upper telescopic rod group, the middle The number of turns of the lead screw in the telescopic rod group and the lower telescopic rod group; the linear induction synchronizer is used to collect the position of the redundant slider on its guide rail; the dead point monitoring processor is used to calculate the speed of the moving platform and the ratio of the speed of the three telescopic rod groups, and compare the ratio with the dead point set value, and determine whether the parallel mechanism is close to the dead point position, and control the expansion and contraction of the three telescopic rod groups and the movement of the redundant slider according to the judgment result. direction to avoid the dead center position. 2. The redundant drive parallel machine tool dead point avoidance system according to claim 1, wherein the dead point monitoring processor comprises a data setting module, a data acquisition module, a speed processing module, a dead point approaching judgment module, motion control module; The data setting module is used to set the dead point setting value; The data acquisition module is used for receiving signals from three encoders and three photoelectric sensors linear induction synchronizers; The speed processing module is used to obtain the telescopic speed of each telescopic rod group according to the output speed of the servo motor in each telescopic rod group measured by the tachogenerator and the transmission ratio in each telescopic rod group, and to measure the telescopic speed of each telescopic rod group according to the photoelectric encoder. The number of turns and the lead of the lead screw in each telescopic rod group can be obtained to obtain the rod length; according to the telescopic speed and rod length of each telescopic rod group, the moving speed of the moving platform can be obtained; The dead point proximity determination module is used to calculate the ratio between the moving speed value of the moving platform and the telescopic speed value of each telescopic rod group, compare the obtained ratio with the set value in the data setting module, and determine whether the mechanism is close to dead point; The motion control module is used to control the expansion and contraction of the three telescopic rod groups and the movement direction of the redundant slider to avoid the dead point position according to whether the mechanism is close to the dead point. 3. The redundant drive parallel machine tool dead center avoidance system according to claim 2, wherein the speed processing module comprises a telescopic rod telescopic speed calculation unit, a telescopic rod rod length calculation unit, and a moving platform motion speed calculation unit; The telescopic rod telescopic speed calculation unit obtains the telescopic speed of each telescopic rod group respectively according to the output speed of the servo motor in each telescopic rod group and the transmission ratio in each telescopic rod group measured by the tachometer generator; The rod length calculation unit of the telescopic rod obtains the rod length according to the number of turns and the lead of the rotation of the lead screw in each telescopic rod group measured by the photoelectric encoder; _The moving platform movement speed calculation unit obtains the moving platform movement speed through the speed _of each telescopic rod group, the rod length, and the speed Jacobian matrix _; Modulo the non-zero telescopic rod group velocity and the moving platform velocity. 4. The redundant drive parallel machine tool dead point avoidance system according to claim 2, wherein the dead point approach determination module calculates the specific process of the ratio of the moving platform movement speed value and the telescopic speed value of each telescopic rod group for: Calculate the ratio between the moving speed value of the moving platform and the telescopic speed value of each telescopic rod group, and compare the obtained ratio with the dead point set value S in the data setting module; if there is any ratio greater than the set value, it means that the mechanism Close to the dead point; if the ratio is not greater than the set value, it means that the mechanism is not close to the dead point. 5. The redundant drive parallel machine tool dead center avoidance system according to claim 4, wherein the motion control module controls the upper and lower telescopic rod sets to lock the servo motors according to the judgment result, if the mechanism is close to the dead center, The middle telescopic rod group can be freely retracted: If the coordinate of the redundant slider on the X axis is less than zero, control the redundant slider to move in the positive direction of the X axis; Conversely, control the redundant slider to move in the negative direction of the X axis. 6. A method for redundantly driving a parallel machine tool dead point avoidance system, characterized in that it comprises the following steps: Step 1. Obtain the output speeds n ₁ , n ₂ , n ₃ of the servo motors in the upper telescopic rod group, the middle telescopic rod group and the lower telescopic rod group; The number of turns a ₁ , a ₂ , a ₃ of the lead screw; the position of the redundant slider on its guide rail to determine the coordinates of the redundant slider on the guide rail; Step 2: Calculate the telescopic speeds v ₁ , v ₂ , v ₃ of the upper telescopic rod group, the middle telescopic rod group and the lower telescopic rod group respectively; calculate the rods of the upper telescopic rod group, the middle telescopic rod group and the lower telescopic rod group respectively length l ₁ , l ₂ , l ₃ ; Step 3. Calculate the speed of the moving platform: the speeds v ₁ , v ₂ , v ₃ and the lengths l ₁ , l ₂ , and l ₃ of each telescopic rod group have been obtained, and the moving speed v _d of the moving platform is obtained through the velocity Jacobian matrix; Calculate the modulo of the non-zero telescopic rod group speed and the moving platform speed; Step 4, determine whether the mechanism is close to the dead point position: calculate the ratio of the moving speed value of the moving platform and the telescopic speed value of each telescopic rod group, and compare the obtained ratio with the dead point setting value S in the data setting module; If there is any ratio greater than the set value, it means that the mechanism is close to the dead point; if the ratio is not greater than the set value, it means that the mechanism is not close to the dead point; Step 5. Control the movement of each telescopic rod group and the redundant slider to avoid the dead center position. 7. The method for redundantly driving a parallel machine tool dead center avoidance system according to claim 6, wherein step 2 calculates the speed of the telescopic rod group and the rod length, and specifically comprises the following steps: 2.1. Calculate the telescopic speed v ₁ , v ₂ , v ₃ of the upper telescopic rod group, the middle telescopic rod group and the lower telescopic rod group: the telescopic speed of the upper telescopic rod group is v ₁ =n ₁ ·i ₁ , the middle telescopic rod group The telescopic speed of the lower telescopic rod group is v ₂ =n ₂ ·i ₂ , and the telescopic speed of the lower telescopic rod group is v ₃ =n ₃ ·i ₃ ; 2.2. Calculate the rod lengths l ₁ , l ₂ , l ₃ of the upper telescopic rod group, the middle telescopic rod group and the lower telescopic rod group: the rod length of the upper telescopic rod group is l ₁ = a ₁ · L ₁ , the middle telescopic rod The rod length of the group is l ₂ =a ₂ ·L ₂ , and the rod length of the lower telescopic rod group is l ₃ =a ₃ ·L ₃ ; Wherein i ₁ , i ₂ , i ₃ are the transmission ratios of the upper telescopic rod group, the middle telescopic rod group and the lower telescopic rod group, respectively; L ₁ , L ₂ , L ₃ are the upper telescopic rod group, the middle telescopic rod group and the lower telescopic rod group, respectively; The lead screw of the telescopic rod set. 8. The method for redundant drive parallel machine tool dead point avoidance system according to claim 6, characterized in that, the step 5 method for avoiding dead point is: If the mechanism is close to the dead center, the servo motors of the upper and lower telescopic rod groups are controlled to be locked, and the middle telescopic rod group can be freely retracted: If the coordinate of the redundant slider on the X axis is less than zero, control the redundant slider to move in the positive direction of the X axis; Conversely, control the redundant slider to move in the negative direction of the X axis.

Images