Servo system force control method, servo driver and chip mounter

Abstract

The invention relates to a servo system force control method, a servo driver and a chip mounter. The method comprises the following steps: acquiring target force and force feedback data determined according to the rigidity of an object; inputting a difference value between the target force and the force feedback data into a servo system to obtain force control position data; the servo system comprises a force controller and a position controller which are connected in sequence; the force control position data is used for determining the action position of the servo system. By adopting the method, the contact force can be controlled with high precision under different object rigidities.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of servo control, in particular to a servo system force control method, a servo driver and a chip mounter. BACKGROUND

[0002] In the application of chip mounting, die picking, camera module assembly and object surface polishing, the force applied to the object needs to be accurately controlled. Too large contact force will cause product damage, and too small contact force will affect product yield. The current force control application scheme usually controls the contact force by limiting the current, which leads to the situation that the impact force when contacting the object is greater than the set force. SUMMARY

[0003] Therefore, it is necessary to provide a servo system force control method, a servo driver and a chip mounter to accurately control the contact force under different object stiffness.

[0004] A servo system force control method, the method comprising:

[0005] obtaining a target force and force feedback data determined according to object stiffness;

[0006] inputting the difference between the target force and the force feedback data into a servo system to obtain force control position data; the servo system comprises a force controller and a position controller connected in sequence; the force control position data is used to determine the action position of the servo system.

[0007] A servo driver comprising a memory and a processor, the memory stores a computer program, and the processor implements the steps of each servo system force control method embodiment when executing the computer program.

[0008] A chip mounter comprising a memory, a processor and an operating arm, the memory stores a computer program, and the processor implements the steps of each servo system force control method embodiment when executing the computer program, and the action position of the servo system is used to control the operating arm.

[0009] A press machine comprising a memory and a processor, the memory stores a computer program, and the processor implements the steps of each servo system force control method embodiment when executing the computer program, and the action position of the servo system is used to apply pressure.

[0010] A computer readable storage medium having a computer program stored thereon, the computer program is executed by a processor to implement the steps of each servo system force control method embodiment.

[0011] A computer program product comprises a computer program which, when executed by a processor, implements the steps of the servo system force control method embodiments.

[0012] The servo system force control method, servo driver and chip mounter described above can obtain force control position data by inputting the difference between the target force and the force feedback data determined according to the object stiffness into the servo system, and use the force control position data to determine the action position of the servo system, thereby achieving high-precision control of the contact force under different object stiffness, adapting to different working conditions and quickly responding to force control requirements. BRIEF DESCRIPTION OF DRAWINGS

[0013] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the related art, the drawings needed to be used in the embodiments or related art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative effort.

[0014] Figure 1 An application environment diagram of the servo system force control method in one embodiment;

[0015] Figure 2 A flowchart of the servo system force control method in one embodiment;

[0016] Figure 3 A structural diagram of the position controller in one embodiment;

[0017] Figure 4 A force control effect diagram in one embodiment. DETAILED DESCRIPTION

[0018] It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the present application.

[0019] The technical solutions in the embodiments of the present application will be described clearly and completely in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present application.

[0020] It should be noted that all the direction indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present application are only used to explain the relative position relationship, movement condition, etc. between components in a certain posture (as shown in the drawings), and if the certain posture changes, the direction indications also change accordingly. The connection can be direct connection or indirect connection.

[0021] In addition, the descriptions such as "first", "second" and the like in the present application are only for the purpose of description, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first", "second" can explicitly or implicitly include at least one of the features. In addition, the technical solutions of various embodiments can be combined with each other, but it must be based on the realization of ordinary skilled in the art, when the combination of technical solutions appears contradictory or unachievable, it should be considered that the combination of technical solutions does not exist, nor within the protection scope required by the present application.

[0022] It can be understood that "connection" in the following embodiments should be understood as "electrical connection", "communication connection" and the like if the connected circuits, modules, units and the like have the transmission of electrical signals or data between each other.

[0023] It can be understood that the operation of "acquiring data" in the embodiments of the present application includes but is not limited to the following implementation manners: directly reading the original data stored in advance in the device; or indirectly acquiring after data acquisition, conversion and processing.

[0024] The servo system force control method provided by the present application can be applied to the application environment such as Figure 1 . Figure 1 Figure 1 is a diagram of an application environment of a servo system force control method in an embodiment. Figure 1 In the servo system, the object stiffness Ke and the force feedback data can be acquired, and the target force Fd can be acquired. The difference between the two is input into the force controller Gf(s) and the position controller Gp(s), and the output is the force control position data.

[0025] Figure 2 is a flowchart of a servo system force control method in an embodiment, including the following steps: Figure 2

[0026] Step 202, acquiring the target force and the force feedback data determined according to the object stiffness.

[0027] Specifically, the target force is the force value that the control system expects to exert on the object, which is usually set by the upper task planning or operation instruction, and the unit is Newton (N).

[0028] ​Object stiffness: refers to the ability of an object to resist deformation under force, usually represented by the elastic coefficient. The higher the stiffness, the smaller the deformation under the same force.

[0029] Force feedback data: refers to the actual force value estimated or measured based on the current system state (such as position, velocity) and the physical characteristics of the object (such as stiffness), used as feedback in the closed-loop control. Force feedback data can be directly measured by force sensors, or can be observed after using the servo system dynamics model. The calculated external force can be determined according to the object stiffness and velocity-related parameters.

[0030] Step 204, input the difference between the target force and the force feedback data into the servo system to obtain force control position data; the servo system includes a force controller and a position controller connected in sequence; the force control position data is used to determine the servo system action position.

[0031] Specifically, the servo system obtains the target force and the force feedback data determined according to the object stiffness, the target force and the force feedback data can be input into a comparator to obtain the difference between them, the difference is input into the force controller Gf(s) for PI control to obtain the reference position value, and then the force control position data output by the position controller Gp(s) is used to determine the servo system action position. That is, the "position set value" calculated by the force controller (PI controller) is a dynamic instruction value, and the function of the position controller is to truly convert this instruction value into the physical position of the motor shaft.

[0032] The force controller is a PI controller:

[0033]

[0034] Where K p is the proportional gain of the controller, T i is the integral gain of the controller, and s is the variable.

[0035] The position controller can be equivalent to:

[0036]

[0037] Where t is the equivalent delay time of the position control, which depends on the position control bandwidth of the servo system, and T is the system delay time when the servo position control is completed.

[0038] In this embodiment, by obtaining the target force and the force feedback data determined according to the object stiffness, the difference between the target force and the force feedback data is input into the servo system to obtain the force control position data, which is used to determine the servo system action position. It can control the contact force with high precision under different object stiffness, can adapt to different working conditions, and can quickly respond to force control requirements.

[0039] In one embodiment, the object stiffness is set as the stiffness of the contact object or measured by contact.

[0040] Specifically, in the case of operating on the same batch of objects, the object stiffness can be set as the stiffness of the contact object without real-time measurement, suitable for standardized production. In the case of unknown stiffness, the system can record multiple sets of indentation and force data in advance to identify the stiffness of the object.

[0041] In this embodiment, the object stiffness is set as the stiffness of the contact object or measured by contact, and by supporting two modes of "preset stiffness" and "measured stiffness", the system can flexibly cope with efficient operation of known materials and adaptive control of unknown materials, significantly expanding the application scenarios.

[0042] In one embodiment, the force feedback data is determined by a single-axis system dynamics model containing speed-related parameters; the speed-related parameters are determined by a finite Fourier series excitation trajectory.

[0043] The single-axis system dynamics model refers to the dynamics equation of the servo system in a single motion direction. The speed-related parameters include the angular velocity of the servo system actuator (such as a joint), and can also include the angle and angular acceleration.

[0044] Specifically, the single-axis system dynamics model can be expressed as

[0045]

[0046] where J is the moment of inertia, G(q) is the gravity moment, τ is the joint torque. q, q, are the angle, angular velocity, and angular acceleration, respectively. c v are the Coulomb friction and viscous friction coefficient, respectively, and sign is the sign function.

[0047] Rewrite the above equation as a linear equation set:

[0048]

[0049] where β = [Jf c v 1] T ,

[0050] Then use the least squares method to solve it. Assuming that m sets of motion data are used, the combined regression equation set is:

[0051]

[0052] where ∈ is the error value of the least squares. ​​

[0053] In the process of identifying the dynamic parameters, enough data need to be collected to solve the problem. The commonly used excitation trajectory is polynomial excitation trajectory and finite Fourier series excitation trajectory. The finite Fourier series excitation trajectory can ensure the smoothness of the motion process and will not have the problem of sudden change of speed and acceleration, so the finite Fourier series excitation trajectory is adopted.

[0054]

[0055] Wherein, q0 is the angular velocity at the initial time, ω f is the base angular velocity of the Fourier series excitation, a k and b k are the coefficients of the Fourier series excitation trajectory, k is the series, and t is the time.

[0056] External contact force prediction: through the previous dynamic parameter identification, the external force can be predicted Force feedback data τ ext

[0057]

[0058] In this embodiment, the force feedback data is determined by the single-axis system dynamics model containing speed-related parameters, which can accurately compensate the dynamic effects such as viscous friction and nonlinear damping in the motion process, and avoid the force estimation error generated by the traditional static model under variable speed working condition; the speed-related parameters are determined by the finite Fourier series excitation trajectory, which can ensure the smoothness of the motion process and will not have the problem of sudden change of speed and acceleration.

[0059] In one embodiment, the force controller is a PI controller, and the output of the force controller is a position command used as an input setting value of the position controller.

[0060] Wherein, the force controller is the core module for realizing force closed-loop control, the input of which is the error between the target force and the force feedback data, and the output of which is the adjustment signal used to drive the lower-level controller. The PI controller is a proportional-integral (Proportional-Integral) controller, and the output of which is linearly superimposed by the proportional term and the integral term of the error.

[0061] Specifically, the force controller is a PI controller:

[0062]

[0063] Wherein, K p is the proportional gain of the controller, T i is the integral gain of the controller, and s is the variable.

[0064] The force controller receives the force error from the feedback link and uses the preset K pand T i The parameters are used to perform proportional and integral calculations on the force error to generate a control output. The output of the PI controller is interpreted as a target position command, which indicates "where the actuator should move to in order to reduce the force error." This position command is sent to the position controller (such as a PID position loop) as its new target position, driving the servo motor to perform the corresponding movement.

[0065] In this embodiment, the force controller is a PI controller, and the output of the force controller is a position command, which is used as the input set value of the position controller. The target position can be adjusted through the outer loop (force loop), and the precise trajectory tracking can be achieved through the inner loop (position loop), thus completing the force control together.

[0066] In one embodiment, the controller integral gain T of the force controller i for

[0067]

[0068] The proportional gain K of the force controller p for

[0069]

[0070] Among them, K e Let T be the object stiffness, T be the equivalent delay time for position control, and ω be the position control stiffness. f Let ξ be the bandwidth of the force control system, and ξ be the damping of the force control loop.

[0071] Specifically, the force controller is a PI controller:

[0072]

[0073] Where K p For the controller proportional gain, T i Let s be the integral gain of the controller, and s be a variable.

[0074] like Figure 3 The diagram shown is a schematic representation of the position controller in one embodiment. Figure 3 The closed-loop transfer function of the position loop can be obtained as follows:

[0075]

[0076] Where, k sp k is the proportional coefficient of the speed loop controller. si k is the integral coefficient of the speed loop controller. t denoted as the motor torque coefficient, and J as the moment of inertia.

[0077] make The above formula can be rewritten as:

[0078]

[0079] Position loop closed loop transfer function:

[0080]

[0081] where ω v is the speed loop bandwidth, ξ v is the speed loop damping, and k pp is the position loop proportional gain.

[0082] Rewriting the position loop transfer function as:

[0083]

[0084] where s0is the controller pole.

[0085] Then a0= ω v / 2ξ v , s0ω p 2 = k pp ω v 2 , (s0+2ξ p ω p )=2ξ v ω v

[0086] ω p 2 +2ξ p ω p s0= ω v 2 +2ξ v ω v k pp

[0087] Let k pp = ω v / n, s0= ω v / m, then

[0088]

[0089] where m is the proportional coefficient of the speed loop bandwidth and the position loop gain, n is the proportional coefficient of the speed loop bandwidth and the pole, ξ p is the position loop damping coefficient, and ω p is the position loop bandwidth.

[0090] From the above formula, we have:

[0091]

[0092] Preferably, m=8 and n=0.5 are selected, and ξ v =3.99, and ξ p =0.98, the position control closed loop can be simplified as

[0093]

[0094] Let Then

[0095] The closed loop transfer function of the whole system is

[0096]

[0097] where K e is the object stiffness, K p is the controller proportional gain, T i is the controller integral gain, and T is the position control equivalent delay time.

[0098] Taking the force control system bandwidth as ω f , the force control closed loop transfer function can be rewritten as

[0099]

[0100] It can be obtained that:

[0101]

[0102] where ξ is the force control loop damping, usually between 0.5 and 2.

[0103] In this embodiment, the integral gain and proportional gain of the force controller determined based on the object stiffness can consider the object stiffness, thereby precisely controlling the force applied to the object, avoiding product damage, and improving product qualification rate.

[0104] In one embodiment, the servo system force control method can be applied to chip mounting, die picking, camera module assembly, object surface polishing, and other application scenarios. The method aims to solve the technical problem of high-precision closed-loop control of contact force under different contact stiffness.

[0105] I. Calculation of virtual force

[0106] 1. Dynamics parameter identification

[0107] The single-axis system dynamics model can be expressed as

[0108]

[0109] where J is the moment of inertia, G(q) is the gravity moment, τ is the joint torque. q, q, are angle, angular velocity, angular acceleration respectively.f c , f v are Coulomb friction and viscous friction coefficient respectively, sign is sign function.

[0110] Rewrite the above equation into linear equation group form:

[0111]

[0112] where β = [Jf c f v 1] T ,

[0113] Then use least square method to solve. Assuming that m groups of motion data are used, the combined regression equation group is:

[0114]

[0115] where ∈ is the error value of least square.

[0116] 2. Excitation trajectory design

[0117] In the process of dynamic parameter identification, enough data need to be collected to solve. Common excitation trajectories are polynomial excitation trajectory and finite Fourier series excitation trajectory. Using finite Fourier series excitation trajectory can ensure the smoothness of the motion process, and there will be no sudden change of speed and acceleration problem, so finite Fourier series excitation trajectory is used.

[0118]

[0119] where q0is the initial angular velocity, ω f is the base angular velocity of Fourier series excitation, a k and b k are the coefficients of Fourier series excitation trajectory, and k is the series.

[0120] 3. External contact force prediction

[0121] Through the previous dynamic parameter identification, the external force can be predicted Force feedback data τ ext

[0122]

[0123] II. Servo system

[0124] The force controller is a PI controller:

[0125]

[0126] where Kp Kp is the controller proportional gain, T i Ki is the controller integral gain.

[0127] As shown in Fig. 1, a structure diagram of the position controller in one embodiment is shown. By Figure 3 the closed loop transfer function of the position loop can be obtained as Figure 3

[0128]

[0129] where k sp is the speed loop controller proportional coefficient, k si is the speed loop controller integral coefficient, k t is the motor torque coefficient, and J is the moment of inertia.

[0130] The force controller is a PI controller:

[0131]

[0132] where K p is the controller proportional gain, T i is the controller integral gain.

[0133] As shown in Fig. 1, a structure diagram of the position controller in one embodiment is shown. By Figure 3 the closed loop transfer function of the position loop can be obtained as Figure 3

[0134]

[0135] where k sp is the speed loop controller proportional coefficient, k si is the speed loop controller integral coefficient, k t is the motor torque coefficient, and J is the moment of inertia.

[0136] Let the above equation can be rewritten as:

[0137]

[0138] The closed loop transfer function of the position loop is:

[0139]

[0140] where ω v is the speed loop bandwidth, ξ v is the speed loop damping, k pp is the position loop proportional coefficient, and s0 is the controller pole.

[0141] Rewrite the position loop transfer function as: ​​

[0142]

[0143] then a0= ω v / 2ξ v , s0ω p 2 = k pp ω v 2 , (s0+2ξ p ω p )=2ξ v ω v

[0144] ω p 2 +2ξ p ω p s0= ω v 2 +2ξ v ω v k pp

[0145] Let k pp = ω v / n, s0= ω v / m, then

[0146]

[0147] where m is the proportional coefficient of the speed loop bandwidth and the position loop gain, n is the proportional coefficient of the speed loop bandwidth and the pole, ξ p is the position loop damping coefficient, and ω p is the position loop bandwidth.

[0148] From the above formula, we have:

[0149]

[0150] Preferably, m=8n=0.5 is selected, which can obtain ξ v =3.99, ξ p =0.98, and the position control closed loop can be simplified as

[0151]

[0152] Let then

[0153] The closed loop transfer function of the entire system is

[0154]

[0155] where K e is the stiffness of the object, and Kp For the controller proportional gain, T i Let T be the integral gain of the controller, and T be the equivalent delay time for position control.

[0156] The bandwidth of the force control system is ω f The force-controlled closed-loop transfer function can be rewritten as follows:

[0157]

[0158] We can obtain:

[0159]

[0160] Where ξ is the force-controlled loop damping, which is usually taken between 0.5 and 2.

[0161] So after obtaining K p and T i After obtaining the two parameter values, the difference between the target force and the force feedback data can be controlled by PI to obtain the reference position value. Then, the force control position data output by the position controller Gp(s) is used to determine the position of the servo system, thereby realizing the control of the force.

[0162] III. Force Control Effect

[0163] like Figure 4 The diagram shown illustrates the force control effect in one embodiment. The horizontal axis represents time, the vertical axis represents force, the blue curve represents the target force, and the yellow curve represents the force feedback value. Figure 4 As can be seen from the method in this embodiment, the force feedback value can follow the command response very well with almost no overshoot.

[0164] In this embodiment, various working conditions can be adapted according to the environmental stiffness. Closed-loop force control can be realized through the tuning of the closed-loop controller, which can quickly respond to force control requirements and can be applied to application scenarios such as voice coil motor chip mounting and presses.

[0165] It should be understood that, although the above Figure 2 The steps in the flowchart are shown sequentially as indicated by the arrows, but these steps are not necessarily executed in the exact order indicated by the arrows or numbers. Unless otherwise specified in this document, there is no strict order in which these steps are performed; they can be executed in other orders. Figure 2 At least some of the steps in the process may include multiple steps or multiple stages. These steps or stages are not necessarily completed at the same time, but may be executed at different times. The execution order of these steps or stages is not necessarily sequential, but may be executed in turn or alternately with other steps or at least some of the steps or stages in other steps.

[0166] In one embodiment, a servo driver is provided, comprising a memory and a processor, the memory storing a computer program, the processor implementing the steps of the above method embodiments when executing the computer program.

[0167] In one embodiment, a chip mounter is provided, comprising a memory, a processor and an operating arm, the memory storing a computer program, the processor implementing the steps of the above method embodiments when executing the computer program, the servo system acting position being used to control the operating arm.

[0168] In one embodiment, a press machine is provided, comprising a memory and a processor, the memory storing a computer program, the processor implementing the steps of the above method embodiments when executing the computer program, the servo system acting position being used to apply pressure.

[0169] In one embodiment, a computer device is provided, comprising a memory and a processor, the memory storing a computer program, the processor implementing the steps of the above method embodiments when executing the computer program.

[0170] In one embodiment, a computer readable storage medium is provided, storing a computer program, the computer program being executed by a processor to implement the steps of the above method embodiments.

[0171] In one embodiment, a computer program product is provided, comprising a computer program, the computer program being executed by a processor to implement the steps of the above method embodiments.

[0172] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a non-volatile computer readable storage medium, and when executed, can include the processes of the above-mentioned embodiment methods. Any reference to memory, database or other medium used in the embodiments provided by the present application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical storage, high-density embedded non-volatile memory, resistive memory (ReRAM), magnetoresistive random access memory (MRAM), ferroelectric memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. As an illustration but not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc. The database involved in the embodiments provided by the present application can include at least one of a relational database and a non-relational database. The non-relational database can include a distributed database based on a block chain, etc., without being limited thereto. The processor involved in the embodiments provided by the present application can be a general-purpose processor, a central processing unit, a graphics processing unit, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, etc., without being limited thereto.

[0173] The above is only the preferred embodiment of the present application, and does not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation using the content of the specification and drawings, or direct or indirect application in other related technical fields, is also included in the patent protection scope of the present application.

Claims

1. A force control method for a servo system, characterized in that, The method includes: Acquire the target force and force feedback data determined based on the object's stiffness; The difference between the target force and the force feedback data is input into the servo system to obtain force control position data; the servo system includes a force controller and a position controller connected in sequence; the force control position data is used to determine the position of the servo system.

2. The method according to claim 1, characterized in that, The stiffness of the object is a set stiffness value for the contacting object or is obtained through contact measurement.

3. The method according to claim 1, characterized in that, The force feedback data is determined by a single-axis system dynamics model containing velocity-related parameters; the velocity-related parameters are determined by a finite Fourier series excitation trajectory.

4. The method according to claim 1, characterized in that, The force controller is a PI controller, and the output of the force controller is a position command, which is used as the input set value of the position controller.

5. The method according to claim 4, characterized in that, The controller integral gain T of the force controller i for The proportional gain K of the force controller p for Among them, K e Let ω be the stiffness of the object, T be the equivalent delay time for position control, and ω be the position control stiffness. f Let ξ be the bandwidth of the force control system, and ξ be the damping of the force control loop.

6. A servo driver, comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 5.

7. A chip mounting machine, comprising a memory, a processor, and a manipulator arm, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 5, wherein the servo system operates at a position for controlling the manipulator.

8. A press, comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 5, wherein the servo system's operating position is used to apply pressure.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 5.

10. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 5.

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