JP6844158B2 - Control device and control program - Google Patents

Description

The present technology relates to a control device and a control program for controlling an actuator.

Conventionally, control devices and control methods for actuators that apply a load have been proposed. As an application example of an actuator that applies such a load, there is a bonding device that performs a process of arranging parts on a substrate. In such a bonding apparatus, when arranging a component on a substrate, there is a need to press the component with a low load so as not to damage the component or the substrate.

In such a bonding operation, high-speed and highly accurate position control is required, and therefore, a moving mechanism using a ball screw is generally adopted. In such a moving mechanism using a ball screw, since the friction generated by the rotation of the ball screw is relatively large, it is difficult to adjust a small range compared to the magnitude of the friction. That is, adjusting the torque in a smaller control range than the torque required to drive the ball screw has accuracy restrictions, and it is not easy to realize pressing control with a low load.

Therefore, the following prior arts have been proposed in order to realize pressing control with a low load.

Japanese Unexamined Patent Publication No. 2011-096840 (Patent Document 1) discloses an electronic component mounting device capable of mounting an electronic component such as a very thin semiconductor chip with a low load that does not cause cracking. .. Further, Japanese Patent Application Laid-Open No. 2013-157529 (Patent Document 2) discloses a die bonder or the like that can obtain an adhesive load from a light load to a high load or can be mounted at high speed.

Japanese Unexamined Patent Publication No. 2011-096840 Japanese Unexamined Patent Publication No. 2013-157529

However, the above-mentioned prior art has the following problems. Japanese Unexamined Patent Publication No. 2011-096840 (Patent Document 1) proposes a configuration using pressure such as a fluid. Such a configuration is sufficient if only the pressing time is taken into consideration, but it is insufficient to realize high-speed and high-precision position control when considering a device configuration in which the amount of movement is large.

Further, in the configuration disclosed in Japanese Patent Application Laid-Open No. 2013-157529 (Patent Document 2), two axes are required and a linear motor is required as an actuator, so that the size and cost of the device are increased. Can arise. Further, for light load operation, a configuration in which a spring is attached to the shaft is adopted, and in this configuration, there may be a problem that the stability of control cannot be maintained due to the aging of the spring.

There is a demand for a configuration that can realize pressing control with a low load at high speed and with high accuracy while adopting a general device configuration.

According to an embodiment of the present invention, there is provided a control device that changes the relative distance between the object and the moving member and controls the magnitude of the load applied from the moving member to the object. The control device sequentially calculates the command value for the moving member according to the pattern of the predetermined speed or position, and when the predetermined first condition is satisfied, the control device determines the command value by the first control means. Instead of the calculation, the second control means for sequentially calculating the command value for the moving member according to the control calculation formula corresponding to the impedance control is included.

Preferably, the control calculation formula corresponding to the impedance control includes a term proportional to the difference between the target value and the actual value for the dimension of the command value.

Preferably, the control calculation formula corresponding to the impedance control further includes a term proportional to the difference between the target value and the actual value for the dimension in which the command value is integrated.

Preferably, the first control means sequentially calculates the speed command value for the moving member according to the pattern for the speed, and the second control means calculates the current speed command value using the actual speed value according to the control calculation formula. To do.

Preferably, the second control means controls the first period including the time point when the moving member comes into contact with the object according to the impedance control set in the first parameter set, and subsequently, the second parameter set different from the first parameter set. The second period following the first period is controlled according to the impedance control for which the parameter set is set.

Preferably, before the moving member comes into contact with the object, the target value for calculating the speed command value for the moving member is reduced by the amount of correction acquired in advance.

Preferably, the second control means calculates the speed command value when a predetermined second condition is satisfied in the process of sequentially calculating the command value for the moving member according to the control calculation formula corresponding to the impedance control. The target value of is reduced by the amount of correction.

Preferably, the second condition includes the elapse of a predetermined time from the start of impedance control by the second control means.

Preferably, the second condition takes into account the peak of the load that occurs immediately after the moving member comes into contact with the object and the length of time required for a series of processes in which the moving member comes into contact with the object and applies the load. It is determined.

According to an embodiment of the present invention, there is provided a control program that changes the relative distance between the object and the moving member and controls the magnitude of the load applied from the moving member to the object. The control program gives the computer a command by the first control step in which the command value for the moving member is sequentially calculated according to a predetermined speed or position pattern, and when the predetermined first condition is satisfied. Instead of calculating the value, the second control step of sequentially calculating the command value for the moving member according to the control calculation formula corresponding to the impedance control is executed.

According to the embodiment of the present invention, pressing control with a low load can be realized at high speed and with high accuracy while adopting a general device configuration.

It is a schematic diagram which shows an example of the actuator used in the control method which concerns on this Embodiment. It is a schematic diagram for demonstrating the change of the force according to the collision speed generated in the pressing control. It is a figure for demonstrating the change of the frictional force shown in FIG. It is a figure which shows an example of the arithmetic expression in the time domain used for the impedance control used in the control method which concerns on this embodiment. It is a schematic diagram which outlines the structure of the control system including the control device which concerns on this embodiment. It is a schematic diagram which outlines the structure of the arithmetic processing unit of the control device shown in FIG. It is a schematic diagram which outlines an example of the control loop for realizing the control method which concerns on this Embodiment. It is a schematic diagram for demonstrating the 1st control logic of the control method which concerns on this Embodiment. It is a flowchart which concerns on the 1st control logic of the control method which concerns on this Embodiment. It is a time chart which shows an example of the control result which follows the 1st control logic of the control method which concerns on this Embodiment. It is a schematic diagram for demonstrating the 2nd control logic of the control method which concerns on this Embodiment. It is a figure for demonstrating the phenomenon that the load peak is generated by the contact between a moving member and an object. It is a schematic diagram for demonstrating the outline of the 3rd control logic of the control method which concerns on this Embodiment. It is a flowchart which concerns on the 3rd control logic of the control method which concerns on this Embodiment. It is a time chart which shows an example of the control result which follows the 3rd control logic of the control method which concerns on this Embodiment. It is a figure which shows an example of the function block for defining the execution of the control method which concerns on this embodiment on a user program. It is a figure which shows an example of the function block for defining the impedance control included in the control method which concerns on this embodiment on a user program. It is a schematic diagram which shows another example of the actuator used in the control method which concerns on this Embodiment.

Embodiments of the present invention will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are designated by the same reference numerals and the description thereof will not be repeated.

<A. Actuator configuration and issues>
First, the configuration and problems of the actuator according to the present embodiment will be described. The control method according to the present embodiment changes the relative distance between the object and the moving member, and controls the magnitude of the load applied from the moving member to the object. As an example of such an actuator, a moving mechanism having a ball screw will be described below as an example.

(A1: Actuator configuration example)
FIG. 1 is a schematic view showing an example of an actuator used in the control method according to the present embodiment. With reference to FIG. 1, the actuator 2 includes a ball screw 6 arranged so as to penetrate an upper portion in a central portion of the housing 4. A nut 8 which is a moving member is engaged with the ball screw 6. The nut 8 is arranged inside the housing 4 in a state where rotation is suppressed. A motor 10 is coupled to one end of the ball screw 6, and when the motor 10 rotates, the ball screw 6 and the nut 8 rotate relative to each other, and as a result, the nut 8 rotates along the axial direction of the ball screw 6. It will move. With such a mechanism, the position of the nut 8 which is a moving member can be controlled.

For example, the object is arranged in the moving direction of the nut 8 which is a moving member. That is, the rotation of the ball screw 6 changes the position of the ball screw 6, so that the relative distance between the object and the moving member changes. Then, the nut 8 or a member (not shown) mechanically connected to the nut 8 comes into contact with the object, so that a load is applied to the object. In the control method according to the present embodiment, the moving member (nut 8) approaches and contacts the object, and controls the magnitude of the load applied to the object by the moving member after the contact.

The actuator as shown in FIG. 1 may be used, for example, in an application such as arranging a component on some substrate.

(A2: Difficulty of pressing control with low load)
Next, the difficulty of pressing control with a low load when the actuator 2 as shown in FIG. 1 is used will be described. The pressing control generally refers to control of the relative distance between the moving member of the actuator 2 and the object, and control of the magnitude of the load applied by the moving member of the actuator 2 to the object. Include.

In the following description, when used only by the term "pressing", it may be intended that the moving member exerts a load on the object. Further, the term "low load" refers to the load applied to the object by the moving member of the actuator 2 as compared with the magnitude of the load (typically, torque) required to drive the actuator 2. Is a concept that includes the case where is relatively small. However, the term "low load" should not be construed in a limited way, but should be construed as a term that outlines a range in which it is difficult to control the magnitude of the load, as described later.

For example, as a high-load pressing control, consider a case where the torque required to drive the ball screw constituting the actuator 2 is 30 Nm and the torque for pressing is 10 Nm. In this case, if a total torque of 40 Nm is applied for pressing, pressing can be performed. At this time, since the torque for pressing is 1/4 of the total torque, the influence of the error generated on the total torque can be substantially ignored.

On the other hand, as a low-load pressing control, consider a case where the torque required to drive the ball screw constituting the actuator 2 is 30 Nm and the torque for pressing is 1 Nm. In this case, logically, if a total torque of 31 Nm is applied for pressing, pressing can be performed. However, in reality, the magnitude of friction changes minutely due to the influence of position, noise, aging, etc., and the torque for actually driving the ball screw changes in the range of about 27 to 33 Nm. Due to such a total torque error, 1 Nm of torque required for pressing a low load is buried.

(A3: Effect of collision speed on load)
Next, the influence on the load generated according to the collision speed between the moving member and the object will be described. When the distance between the moving member and the object is closer than the original value due to an error in the size of the object or the moving member, and an overshoot occurs in the pressing control, the direction of the generated friction changes. Therefore, pressing control may not be performed properly.

FIG. 2 is a schematic diagram for explaining a change in force according to a collision speed generated in pressing control. FIG. 3 is a diagram for explaining the change in the frictional force shown in FIG. The reason why the pressing force (load) changes according to the collision speed will be described with reference to FIGS. 2 and 3.

In each of the examples shown in FIGS. 2A to 2C, it is assumed that the output torque is maintained at a value corresponding to 20% of the rated value, and the force generated by the actuator 2 at this time is 20N. Suppose there is. Further, the frictional force at rest (static frictional force) fluctuates within a certain range depending on the situation.

FIG. 2A shows a case where the moving member collides with the object at a low speed. With reference to FIG. 2A, the forces generated by the actuator 2 are the repulsive force (that is, the pressing force (load)) generated from the object when the moving member collides with the object, and the ball screw. Corresponds to the sum of the friction caused by the rotational drive of. For example, if the collision speed of the moving member against the object is low and the pressing force against the object is 10N, the force generated by the actuator 2 is constant at 20N, so that the frictional force corresponding to 10N is generated. appear.

FIG. 2B shows a case where the moving member collides with the object at high speed. Assuming that the collision speed of the moving member with respect to the object is high and the pressing force against the object is 50 N at the moment of collision with reference to FIG. 2 (B), the maximum magnitude is on the negative side. (In the example shown in FIG. 2B, -10N) is generated, but it cannot be balanced with the force (20N) generated by the actuator 2, and the moving member is pushed back to the level before the collision. Is to move in the opposite direction.

As a result, while the moving member is pushed back after the collision, the pressing force against the object is reduced to 30N, and the maximum frictional force on the negative side (-10N in the example shown in FIG. 2B). ) Is balanced.

FIG. 2C shows a case where the moving member collides with the object at a medium speed. Assuming that 25N of the pressing force against the object is generated with reference to FIG. 2C, the force generated by the actuator 2 is constant at 20N, so that a frictional force corresponding to 5N is generated on the negative side.

As shown in FIGS. 2A to 2C, the magnitude of the frictional force that can be generated in the actuator 2 is arbitrary depending on the magnitude of the impact force generated according to the collision speed between the moving member and the object. It will change non-linearly (between static friction and dynamic friction). For example, in the model showing the magnitude of the frictional force generated in the actuator 2 shown in FIG. 3, the static friction can take an arbitrary value in the range of -10N to 10N, and when it exceeds this range, it exceeds the value. The moving member (nut 8) will move in the direction.

<B. Overview>
As described above, it is difficult to control the pressing with a low load, and high-speed and highly accurate position control is required. In response to such a requirement, in the control method according to the present embodiment, speed command type impedance control or position command type impedance control is adopted.

"Impedance control" as used herein includes a control method for adjusting a corresponding position and speed according to the mechanical impedance (damping characteristics, rigidity, inertia) of a controlled object. Specifically, a control calculation formula that includes a "damper term" corresponding to damping characteristics, a "spring term" corresponding to rigidity, and a "mass term" corresponding to inertia as factors is adopted. However, it is not necessary to adopt a control calculation formula that includes all of these terms, and at least one that includes a "mass term" and a "damper term" may be used.

FIG. 4 is a diagram showing an example of an arithmetic expression in the time domain used for impedance control used in the control method according to the present embodiment. In FIGS. 4A to 4C, x _n is a variable representing the position at time n, and the dot (.) At the top of the variable indicates the time derivative. Those with two dots (...) at the top of the variable indicate the second derivative of time.

FIGS. 4 (A) to 4 (C) show control calculation formulas when the speed command value at time n is sequentially calculated (speed command type). That is, the speed command value at time n is calculated by adding the time integral of the acceleration at each time to the speed command value at the previous time (time n-1). The acceleration includes at least a part of a mass term, a damper term, a spring term, and a mass term (load), as shown in the third equation of FIGS. 4A to 4C. In the case of adopting the case of sequentially calculating the position command value at time n (position command type), the control calculation formulas shown in FIGS. 4A to 4C may be further integrated over time. Since the calculation of the position command value from the speed command value is a known technique, the detailed description thereof will not be given here.

Each variable in the equations of FIGS. 4A to 4C means the following.
x _n (・): Speed command value x _n-1 (・): Actual speed value x _d (・): Speed target value (current target value)
m _d : Mass coefficient C _d : Damper coefficient K _d : Spring coefficient x _d : Position target value (current target value)
x _n-1 : Actual position value F _d : Target load value F _ext : Actual load value Δt: Calculation cycle (sampling time)
In Figure 4 the control calculation formula (A), the reciprocal of the mass coefficient m _d is used as a mass term, the inverse of the mass coefficient m _d is the damper section Baneko, with respect to the total mass section (load) Be multiplied. The mass coefficient m _d is a coefficient associated with the mass of the moving member.

As the damper term, a value obtained by multiplying the difference between the current speed target value and the previous speed actual value (time n-1) by the damper coefficient C _{d is adopted.} As described above, the control calculation formula corresponding to the impedance control includes a term proportional to the difference between the target value and the actual value for the dimension of the command value (velocity in the example shown in FIG. 4).

As the spring term, a value obtained by multiplying the difference between the current position target value and the previous position actual value (time n-1) by the spring coefficient K _{d is adopted.} It includes a term proportional to the difference between the target value and the actual value for the dimension (position in the example shown in FIG. 4) in which the command values are integrated.

As the mass term (load), a value obtained by multiplying the difference between the load target value to be generated by the actuator and the actual load value actually generated by -1 is adopted. The measured value in the load cell 16 described later is typically used to acquire the actual load value _ext.

The control calculation formula shown in FIG. 4 (B) corresponds to the one excluding the mass term (load) in FIG. 4 (A), and is simplified when the load applied to the object from the actuator cannot be fed back. The control calculation formula given may be adopted.

The control calculation formula shown in FIG. 4 (C) corresponds to the one excluding the spring term in FIG. 4 (B), and when the disturbance caused by the rigidity of the actuator or the moving member can be ignored, this control calculation is performed. The formula may be adopted.

In the control calculation formulas shown in FIGS. 4A to 4C, the mass coefficient m _d , the damper coefficient C _d , the spring coefficient K _d , the actuator-specific values in each term, and the like are preset according to the control system. ..

In the control method according to the present embodiment, the impedance control as described above is adopted. By adopting such impedance control, pressing control can be performed at high speed and with high accuracy even for an actuator that drives a ball screw with a servo motor instead of a linear motor. Therefore, unlike the configuration disclosed in Patent Document 2 described above, a configuration that avoids an increase in size and cost of the device and does not require an element such as a spring that lowers the stability of control due to aging. realizable.

<C. Control system configuration>
Next, a configuration of a control system including a control device for realizing the control method according to the present embodiment will be described. FIG. 5 is a schematic diagram illustrating the configuration of the control system 1 including the control device according to the present embodiment.

With reference to FIG. 5, the control system 1 includes a control device 100 that is mainly responsible for controlling the actuator 2. The control device 100 may be implemented using an arbitrary computer, hardware logic, or the like, but in the following description, a case where a PLC (programmable controller), which is an example of an industrial computer, is typically described. ..

The control device 100 includes an arithmetic processing unit 102 and one or more functional units 104-1, 104-2, 104-3, 104-4, ... (Hereinafter, also collectively referred to as "functional unit 104"). ..

FIG. 6 is a schematic diagram illustrating the configuration of the arithmetic processing unit 102 of the control device 100 shown in FIG. With reference to FIG. 6, in the arithmetic processing unit 102, the processor 110 executes the system program 122 and the user program 116 to provide various processes including the control method according to the present embodiment.

Specifically, the arithmetic processing unit 102 includes a processor 110, a main memory 112, a secondary storage device 114, a bus master circuit 124, a local interface circuit 126, and a network master circuit 128 as main components.

The processor 110 is an arithmetic unit that sequentially executes instructions described in various programs, and is typically composed of a CPU (Central Processing Unit), a GPU (Graphical Processing Unit), and the like. As the processor 110, any of a multi-core configuration, a multi-processor configuration, and a configuration in which both are combined may be adopted.

The main memory 112 is a storage device that provides a work area when the processor 110 executes a program. As the main memory 112, a volatile memory such as a DRAM (Dynamic Random Access Memory) or a SRAM (Static Random Access Memory) is used.

The secondary storage device 114 stores various programs and various configurations executed by the processor 110. As the secondary storage device 114, a non-volatile memory such as an HDD (Hard Disk Drive) or an SSD (Solid State Drive) is used. More specifically, the secondary storage device 114 stores the system program 122 and the user program 116. The system program 122 is a program corresponding to a kind of operating system, and provides a basic system function provided by the arithmetic processing unit 102 or an environment for executing the user program 116. The user program 116 is a kind of control program arbitrarily created according to the control target of the control device 100, and typically includes a sequence program 118 mainly for logical operations, position control, speed control, and the like. Includes a motion program 120 mainly for numerical calculation of. The control method according to this embodiment may be implemented as a part of the motion program 120.

The bus master circuit 124 manages data transmission on the internal bus that exchanges data with the functional unit 104 (see FIG. 5).

The local interface circuit 126 is an interface for exchanging data with a support device and other external devices, and for example, a transmission standard such as USB (Universal Serial Bus) is adopted.

The network master circuit 128 manages data transmission on a field network that exchanges data with a functional unit and other control devices arranged at a position distant from the control device 100. As such a field network, a periodic network such as EtherCAT (registered trademark), EtherNet / IP (registered trademark), DeviceNet (registered trademark), and CompoNet (registered trademark) is used.

With reference to FIG. 5 again, the functional unit 104 connected to the arithmetic processing unit 102 provides various functions for realizing arbitrary control of the controlled object by the control device 100. Typically, each of the functional units 104 outputs a function of collecting field information from a machine or equipment to be controlled (data collection function) and / or a command signal to the machine or equipment to be controlled. It has a function (data output function) and the like.

In the configuration shown in FIG. 5, the functional unit 104-4 functions as a servo control unit, and is calculated at predetermined intervals by executing a program (mainly the motion program 120 shown in FIG. 6) in the arithmetic processing unit 102. The command value (typically, the speed command value or the position command value) is given to the servo driver 14.

The servo driver 14 drives the motor 10 (servo motor in the example shown in FIG. 5) according to the command value from the control device 100. Typically, the servo driver 14 outputs a number of pulses corresponding to the command value from the control device 100 to the motor 10, and the motor 10 changes the rotation position according to the number of received pulses. By adopting such a configuration, the rotation position, rotation angular velocity, rotation angular acceleration, and the like of the motor 10 can be controlled by appropriately adjusting the number of pulses given to the motor 10.

In the configuration shown in FIG. 5, a counter 12 for feeding back the rotational behavior of the motor 10 is arranged, and the servo driver 14 adjusts an electric signal given to the motor 10 based on a value detected from the counter 12. .. That is, the servo driver 14 has a feedback loop based on the actual value of speed or position.

Further, a load cell 16 for measuring the load generated on the object by the pressing control may be provided. The detected value of the load cell 16 is given to the functional unit 104-3 which is an input unit. The load cell 16 is, so to speak, for verification and is an option. Further, instead of actually arranging the load cell 16, an observer or the like may be used to estimate the load that may be generated on the object.

<D. Control loop>
Next, an example of a control loop for realizing the control method according to the present embodiment will be described. FIG. 7 is a schematic diagram illustrating an example of a control loop for realizing the control method according to the present embodiment. FIG. 7 shows a control loop corresponding to the control calculation formula shown in FIG. 4B described above.

With reference to FIG. 7, the control method according to the present embodiment is realized by the control loop mounted in the control device 100, the servo driver 14, and the peripheral portion. Specifically, the control loop of the control device 100 includes coefficient arithmetic units 152, 156, 160, 162, addition / subtractors 154, 158, 164, a differentiator 168, and a switch 180.

As will be described later, the control method according to the present embodiment is realized by combining impedance control and control methods other than impedance control. A switch 180 is provided to switch the output of two or more control systems. The speed command value by impedance control appears in the first port 166 to which the switch 180 can be selected, and the speed command value by speed control appears in the second port 170.

The differentiator 168 time-differentiates the input position target value and outputs the velocity target value.

A position target value x _d is sequentially given to the _{coefficient calculator 152, and the magnitude thereof is multiplied by k d} / d _d and output. In the addition / subtractor 154, the velocity target value from the differentiator 168 is added to the _{coefficient-corrected position target value x d output from the coefficient calculator 152, and the actual position value is subtracted.}

The coefficient calculator 156, the operation result from the adder 154 is given sequentially, its magnitude is output is c _d times. In the addition / subtractor 158, the actual speed value is added to the coefficient-corrected addition result output from the coefficient calculator 156.

The calculation results from the addition / subtraction device 158 are sequentially given to the coefficient calculator 160, and the magnitude thereof is _{multiplied by m d-} ¹ and output. Further, the coefficient calculator 162 is sequentially given the calculation results from the coefficient calculator 160, multiplied by the calculation cycle Δt, and output.

Finally, in the addition / subtractor 164, the calculation result from the coefficient calculator 162 and the actual speed value (previous value) are added and output to the first port 166 as a speed command value.

On the other hand, the speed target value obtained by time-differentiating the input position target value with the differentiator 168 is output to the second port 170.

Incidentally, shown in FIG. 7, the coefficient _{m d, k d, d d} , c d has been convenience introduction of control operations, shown in FIG. 4, the mass coefficient _{m d,} spring coefficient _{K d,} the damper coefficient C Corresponds to _d.

In addition, in the case of reflecting the term of the actual load value (mass term (load)) as shown in FIG. 4 (A), a calculator that reflects the actual load value detected in the load cell 16 may be further added. Good. Alternatively, instead of actually arranging the load cell 16, an observer or the like may be used to estimate the load that can be generated on the object.

On the other hand, the speed command value selected by the switch 180 is given to the servo driver 14, and the servo driver 14 outputs an electric signal for driving the motor 10. The actual speed value based on the value detected by the counter 12 is fed back to the servo driver 14, and the motor 10 is driven so as to follow the given speed command value.

Although the speed command value is hooded back to the control loop related to impedance control, the servo driver 14 also forms a feedback loop for the speed (or position) of the motor 10 to cope with fluctuations in friction caused by the actuator. Compensation can be performed at a higher speed, and pressing control with a low load can be realized with higher accuracy.

Although FIG. 7 shows a speed command type control loop, a position command type control loop can be similarly configured.

<E. 1st control logic>
In the control method according to the present embodiment, the load can be controlled with high accuracy by adopting the impedance control as described above. In impedance control, the actuator 2 is controlled in consideration of the mechanical characteristics (that is, impedance) of the controlled object, so that the load can be adjusted with high accuracy, but the load is closer to the object as compared with the conventional control method. It may take more time to do.

Therefore, in the first control logic of the control method according to the present embodiment, the moving member is brought closer to the object according to the speed control method or the position control method other than the impedance control, and then the impedance control is switched to.

FIG. 8 is a schematic diagram for explaining the first control logic of the control method according to the present embodiment. The horizontal axis defines the elapsed time, and the vertical axis defines the position of the moving member and the generated load.

In the example shown in FIG. 8, a command value is given to the motor 10 according to a predetermined speed target value, that is, a speed pattern (“speed control” shown in FIG. 8). Then, when the moving member approaches the object (in the example shown in FIG. 8, when the time A is reached), the impedance control is switched to.

In the first speed control, the speed pattern is given as a speed command value as it is in order to bring the moving member closer to the object in the shortest possible time. As such a speed pattern, it is preferable that residual vibration does not occur during or after switching to impedance control during speed control control. For example, an orbit (for example, which can be defined by a quintic function for time) may be adopted so that the jerk of the target velocity pattern becomes small.

In addition, instead of the speed control, a control (position control) that gives a predetermined trajectory, that is, a position pattern may be adopted. In this case, the position where the moving member should exist is sequentially given for each time, and the motor 10 is driven according to the position target value.

When the impedance control is switched to after such speed control or position control, the speed command value to the motor 10 is sequentially calculated so that the moving member comes into contact with the object at substantially zero speed. Each parameter of impedance control is adjusted so that the moving speed of the moving member becomes almost zero at the timing when the moving member comes into contact with the object.

When the moving member comes into contact with the object, a load is generated on the object (see reference numeral Z1 in FIG. 8). In the example shown in FIG. 8, it can be seen that the constant load assumed in advance is maintained by the moving member coming into contact with the object and maintaining the velocity at almost zero.

As described above, in the first control logic of the control method according to the present embodiment, the command value (speed command value or position command value) for the moving member is sequentially calculated according to the predetermined speed or position pattern. When the first control loop and the predetermined switching condition are satisfied, the command value (speed command value or position) for the moving member is changed according to the control calculation formula corresponding to the impedance control instead of the calculation of the command value by the first control means. It is combined with a second control loop that sequentially calculates the command value). By adopting such control logic, speed control or position control is performed before impedance control, and the time until the moving member approaches the object can be shortened, and before the two come into contact with each other. By switching to impedance control, the load applied from the moving member to the object can be kept constant.

In the example shown in FIG. 8, in the first control loop, the speed command value for the moving member is sequentially calculated according to the speed pattern (velocity target value), and in the second control loop, the control calculation formula related to impedance control. According to this, the current speed command value is calculated using the actual speed value.

The condition for switching from speed control or position control to impedance control (time A in FIG. 8) is determined according to the end of a predetermined speed pattern or position pattern, that is, the arrival of a predetermined time from the start of control. Good. That is, the switching timing between the speed control or the position control and the impedance control is determined according to the time. Alternatively, the position of the moving member may be estimated based on a speed command or the like, and the switching timing may be determined based on the remaining distance calculated from the estimated position.

FIG. 9 is a flowchart relating to the first control logic of the control method according to the present embodiment. Each step shown in FIG. 9 is typically realized by the processor 110 of the arithmetic processing unit 102 of the control device 100 executing the user program 116.

With reference to FIG. 9, the processor 110 performs setup such as reading parameters required for speed control (or position control) and impedance control (step S100). Subsequently, when the control start is triggered (YES in step S102), the speed command value is calculated according to a predetermined target speed pattern (step S104). The calculated speed command value is given to the servo driver 14.

Subsequently, the processor 110 determines whether or not the switching condition from the speed control to the impedance control is satisfied (step S106). If the condition for switching from the speed control to the impedance control is not satisfied (NO in step S106), the processing of step S104 and subsequent steps is repeated.

If the switching condition from the speed control to the impedance control is satisfied (YES in step S106), the processor 110 calculates the speed command value according to the control calculation formula related to the impedance control (step S108). The calculated speed command value is given to the servo driver 14.

Subsequently, the processor 110 determines whether or not the control end condition is satisfied (step S110). If the speed end condition is not satisfied (NO in step S110), the process of step S108 or less is repeated.

On the other hand, if the speed end condition is satisfied (YES in step S110), the control operation of the example ends.

FIG. 10 is a time chart showing an example of a control result according to the first control logic of the control method according to the present embodiment. FIG. 10 shows an example in which a moving member is brought into contact with an object at a moving speed of 1.1 mm / s, and after the contact between the two members, a load of 15 gf is applied to the object in 15 ms. With reference to FIG. 10, it can be seen that after the moving member comes into contact with the object, the generated load rises substantially linearly, there is no excessive overshoot, and the target is stable at 15 gf.

As described above, according to the control logic 1 of the present embodiment, it can be seen that the pressing control can be performed at high speed and with high accuracy.

<F. 2nd control logic>
In the above-mentioned first control logic, the configuration for switching from speed control or position control to impedance control has been illustrated, but impedance control may be further subdivided.

More specifically, as a physical phenomenon that is the target of impedance control, there are a phase in which the moving member comes into contact with the object and a phase in which a stable load is applied to the object. Therefore, the parameters used for impedance control may be different for the period from before the moving member comes into contact with the object to immediately after the contact and the period after the moving member comes into contact with the object.

FIG. 11 is a schematic diagram for explaining the second control logic of the control method according to the present embodiment. The horizontal axis defines the elapsed time, and the vertical axis defines the position of the moving member and the generated load.

In the example shown in FIG. 11, a command value is given to the motor 10 according to a predetermined speed target value, that is, a speed pattern (“speed control” shown in FIG. 11). Then, when the moving member approaches the object (in the example shown in FIG. 11, when the time A is reached), the impedance control 1 is switched to. In this impedance control 1, parameters are set so that the moving member comes into contact with the object at almost zero speed.

After that, when the moving member comes into contact with the object and the load on the object increases (in the example shown in FIG. 11, when the time B is reached), the impedance control 1 is switched to the impedance control 2. In this impedance control 2, parameters are set so that fluctuations in the magnitude of the load applied to the object converge at an early stage and a load of a stable magnitude is generated.

Specific implementation methods, depending on the impedance control 1 and 2, the coefficient _{m d, k d, d d} , parameter set c _d is prepared in advance, in the control loop shown in FIG. 7, the impedance control 1 When switching from to impedance control 2, the parameter set is switched.

In the second control logic, the first period (time A to B in FIG. 11) including the time point when the moving member comes into contact with the object is controlled according to the impedance control (impedance control 1) in which the first parameter set is set. Subsequently, the second period (after time B in FIG. 11) following the first period is controlled according to the impedance control in which the second parameter set different from the first parameter set is set.

As described above, the control accuracy of the pressing control can be further improved by making the parameters used for the impedance control different according to the situation of the controlled object. As described above, according to the second control logic of the present embodiment, it is possible to realize further high speed and higher accuracy of the pressing control as compared with the above-mentioned first control logic.

<G. Third control logic>
Next, a control logic including a method for reducing a load peak (overshoot) that may occur when the moving member and the object come into contact with each other will be described.

According to the above-mentioned pressing control, high speed and high accuracy can be realized by optimizing the impedance control parameters. However, depending on the device configuration, a load peak (overshoot) may occur immediately after the moving member negotiates with the object. For example, when the tip of the moving member is made of rubber or the like, the load peak is not so high, but when it is made of metal, a large load peak may occur. If the load peak is large, the object may be damaged.

FIG. 12 is a diagram for explaining a phenomenon in which a load peak is generated due to contact between a moving member and an object. With reference to FIG. 12A, the reason why the load peak occurs due to the contact between the moving member and the object is that the speed of the moving member at the time of contact is relatively high. That is, when the moving member comes into contact with an object at a certain speed, a load peak occurs. Considering such a cause, as shown in FIG. 12B, if the speed at the time of contact between the moving member and the object can be made substantially zero, the load peak will occur.

However, in reality, it is not easy to adjust the parameters so that the speed at the time of contact between the moving member and the object becomes almost zero. In particular, in the present embodiment, since impedance control is adopted, a plurality of parameters (mass coefficient m _d shown in FIG. 4, damper coefficient C _d , spring coefficient K _{d / coefficients m d} , k _d shown in FIG. 7), d _d, it is necessary to adjust _{c d)} simultaneously, it takes a lot of man-hours for adjustment work.

Further, it is not preferable that the time (tact time) required for executing the entire control is significantly extended by setting the speed at the time of contact between the moving member and the object to zero.

Therefore, we will optimize the man-hours for adjusting the parameters related to impedance control and adopt a method that can suppress the increase in the tact time of the entire control. Specifically, when some kind of load peak occurs in impedance control according to a certain parameter, the moving speed at the time of contact between the moving member and the object is obtained based on the actual results of the behavior, and the obtained moving speed is calculated. Correct in advance. That is, before the moving member comes into contact with the object, the target value for calculating the speed command value for the moving member is reduced by the previously acquired moving speed (corresponding to the correction amount). This pre-speed correction may be performed in impedance control or in speed control or position control performed prior to switching to impedance control.

FIG. 13 is a schematic diagram for explaining the outline of the third control logic of the control method according to the present embodiment. As shown in FIG. 13 (A), it is assumed that a weighted peak occurs in impedance control according to a certain parameter. By acquiring the behavior in such an unfavorable state, it is possible to acquire the moving speed at the time of contact between the moving member and the object. In the example shown in FIG. 13A, it can be seen that the speed of the moving member at the time of contact (at the time when the load starts to be generated) is X.

With reference to FIG. 13 (B), based on the knowledge obtained in FIG. 13 (A) (the velocity of the moving member at the time of contact is X), the trajectory when the moving member approaches the object is determined. to correct. That is, during impedance control (or earlier speed control or position control), the speed target value is reduced by the correction amount X acquired in the previous knowledge. The speed target value is a reference value for calculating the speed command value of the moving member, and this reference is decremented by the correction amount X acquired in advance.

When the speed correction is performed in advance in the impedance control, the target value for calculating the speed command value is corrected in the control loop that follows the impedance control. At this time, since the speed command value smoothly follows the corrected target value, residual vibration is unlikely to occur in the moving member even when the correction amount is relatively large, and the moving member comes into contact with the object. At that time, it is possible to reduce the possibility that an unintended large force is generated due to residual vibration.

On the other hand, when the speed correction is performed in advance in the speed control or the position control, the speed command value follows the corrected target value with almost no delay. At this time, since the degree of dependence between the parameters related to speed control or position control including the correction of the target value and the parameters related to impedance control can be reduced, there is a possibility that the man-hours for adjusting the parameters can be further reduced.

Further, the speed switching time Tc, which is the timing for reducing the speed target value by the correction amount X, is one adjustable parameter.

As a specific implementation form, in the control loop shown in FIG. 7, a subtractor is arranged on the output side of the differentiator 168 so that the correction amount X is reduced with respect to the speed target value output from the differentiator 168. May be good. According to such an implementation, the timing for reducing the correction amount X will be adjusted according to the relationship between the speed switching time Tc and the switching time between the impedance control and the control method other than the impedance control (speed control or position control). It can be set arbitrarily on the side of.

Setting the speed switching time Tc later is advantageous for shortening the tact time, but is disadvantageous for suppressing the peak load. On the contrary, setting the speed switching time Tc earlier is advantageous for suppressing the peak of the load, but is disadvantageous for shortening the tact time. The speed switching time Tc is adjusted so as to satisfy both the mutually contradictory purposes of suppressing the load peak and reducing the tact time.

However, since only one parameter called the speed switching time Tc needs to be adjusted, the man-hours related to the parameter adjustment do not increase significantly, and the parameter adjustment can be completed with a reasonable man-hour.

In the third control logic, when a predetermined condition is satisfied in the process of sequentially calculating the speed command value for the moving member according to the control calculation formula corresponding to the impedance control (for example, when the speed switching time Tc arrives). ), The target value (in this example, the speed target value) is decremented by the correction amount X acquired in advance. By adopting such a configuration, by adjusting one parameter, which is a condition for reducing the target value by the correction amount X (for example, speed switching time Tc), adjustment for suppression of load peak and suppression of increase in tact time can be performed. It can be realized with a small number of man-hours.

As an example of the condition for reducing the target value by the correction amount X, it may be adopted that a predetermined time (speed switching time Tc) has elapsed from the start of the impedance control. Next, some methods for determining the speed switching time Tc, which is an example of the condition for reducing the target value by the correction amount X, will be described.

(1) Method of using the evaluation function for the load peak and the tact time The speed switching time Tc may be optimized by using the evaluation function for the load peak and the tact time. For example, the following evaluation value f may be defined, and a condition in which the evaluation value f takes a minimum value may be searched.

Evaluation value f = Weight coefficient 1 x Extension of tact time + Weight coefficient 2 x Size of load peak By using such evaluation value f, the speed switching time Tc considering both load peak and tact time can be obtained. Can be decided.

(2) Method using the evaluation function for the takt time When the extension of the takt time is minimized within the range where the load peak satisfies the predetermined allowable value, the following evaluation value f is used. You may.

Evaluation value f = Weight coefficient 1 x Extension of takt time However, load peak <allowable value By using such an evaluation value f, the speed at which the tact time can be shortened to the minimum within the range where the load peak can be maintained within the allowable value. The switching time Tc can be determined.

(3) Optimal value search method As a method for searching for the optimum value of the evaluation value f as described above, a method of finding a solution mathematically may be adopted, but a plurality of candidates are set in advance and a plurality of these candidates are set in advance. You may try to determine the best one among the candidates.

For example, a section in which impedance control is executed (for example, a section from time A to time B in FIG. 11) is divided into N equal parts to set candidate points, and an evaluation value f is sequentially calculated from candidate points close to time A. Then, the speed switching time Tc may be determined based on the calculated evaluation value f.

Alternatively, a section in which impedance control is executed (for example, a section from time A to time B in FIG. 11) is divided into N equal parts to set candidate points, and the intermediate point of the set candidate points is used as the initial value to set the load. If the peak is too high, a candidate point closer to time A is selected, and conversely, if the load peak is below the permissible value, a candidate point closer to time B is selected. Good.

Typically, one of the above-mentioned methods may be used to search for the optimum value among the plurality of candidate points. In this way, the conditions for reducing the target value by the correction amount X are the peak of the load generated immediately after the moving member comes into contact with the object and the time required for a series of processes in which the moving member comes into contact with the object and applies the load. It may be determined in consideration of the length of (tact time).

In the above description, the case where the speed switching time Tc is used as a parameter has been illustrated, but the speed target value may be reduced by the correction amount X according to the position and / or speed condition of the moving member. Good. That is, for example, when the position of the moving member reaches a predetermined speed switching position and / or when the moving speed of the moving member reaches a predetermined speed switching speed, the speed target value in the impedance control is corrected. It may be reduced by X.

FIG. 14 is a flowchart relating to the third control logic of the control method according to the present embodiment. Each step shown in FIG. 14 is typically realized by the processor 110 of the arithmetic processing unit 102 of the control device 100 executing the user program 116.

With reference to FIG. 14, the processor 110 performs setup such as reading parameters required for speed control (or position control) and impedance control (step S200). Subsequently, when the control start is triggered (YES in step S202), the speed command value is calculated according to a predetermined target speed pattern (step S204). The calculated speed command value is given to the servo driver 14.

Subsequently, the processor 110 determines whether or not the switching condition from the speed control to the impedance control is satisfied (step S206). If the switching condition from the speed control to the impedance control is not satisfied (NO in step S206), the processing of step S204 or less is repeated.

If the switching condition from the speed control to the impedance control is satisfied (YES in step S206), the processor 110 calculates the speed command value according to the control calculation formula related to the impedance control (step S208). The calculated speed command value is given to the servo driver 14.

Subsequently, the processor 110 determines whether or not the speed switching condition is satisfied (step S210). The speed switching condition includes the speed switching time Tc and the like as described above. If the speed switching condition is not satisfied (NO in step S210), the processing of step S208 and subsequent steps is repeated.

On the other hand, if the speed switching condition is satisfied (YES in step S210), the processor 110 reduces the speed target value in the impedance control by the correction amount X (step S212). Then, the processor 110 continues to calculate the speed command value so as to be continuous with the reduced speed target value according to the control calculation formula related to the impedance control (step S214).

Subsequently, the processor 110 determines whether or not the control end condition is satisfied (step S216). If the control end condition is not satisfied (NO in step S216), the processing of step S214 and subsequent steps is repeated.

On the other hand, if the control end condition is satisfied (YES in step S216), the control operation of the example ends.

FIG. 15 is a time chart showing an example of a control result according to the third control logic of the control method according to the present embodiment. FIG. 15 (A) shows an example of measurement results by a control method combining speed control and impedance control, and FIG. 15 (B) shows impedance in addition to the control method shown in FIG. 14 (A). An example of the measurement result in the control method in which the speed target value is corrected at a predetermined timing in the control is shown.

FIG. 15 shows an example in which a moving member is brought into contact with an object, and after the contact between the two members, a load of 100 gf is applied to the object.

In the measurement result shown in FIG. 15A, the peak load is 195 gf, which is an overload of 95 gf with respect to the set load of 100 gf. However, no bound (insufficient weighting after the occurrence of the weighted peak) has occurred, and it can be seen that the setting is appropriate in that sense. On the other hand, in the measurement result shown in FIG. 15B, the peak load is reduced to 135 gf, and is suppressed by an overload of 35 gf with respect to the set load of 100 gf. Further, it can be seen that no bounce (insufficient weighting after the occurrence of the weighted peak) has occurred, and the setting is more preferable as compared with the measurement result shown in FIG. 15A.

<H. Implementation example>
Next, a configuration example when the control method according to the present embodiment is implemented on the user program 116 will be described.

FIG. 16 is a diagram showing an example of a function block for defining the execution of the control method according to the present embodiment on the user program. FIG. 17 is a diagram showing an example of a function block for defining impedance control included in the control method according to the present embodiment on a user program. The control method according to the present embodiment is implemented on a program by combining the function block shown in FIG. 16 and the function block shown in FIG.

The function block shown in FIG. 16 is assumed to be used in an existing control loop, and a variable in which a speed command value is stored in the existing control loop is associated with the input port of "PreVelocity", and this control is performed. A variable in which the speed command value after being corrected by the method is stored is associated with the output port of "PreVelocity".

The function block shown in FIG. 17 sets impedance control parameters and the like applied to the speed command value input to the function block shown in FIG. Target values and required parameters are set for each input port of this function block.

By adopting the function blocks as shown in FIGS. 16 and 17, the user can use the desired control on the user program without understanding the specific algorithm of the control method. The scope of application can be expanded.

<I. Application example>
In the above description, an application example for providing a control method according to an embodiment for an actuator in which a moving member moves along a drawing direction of a ball screw has been illustrated, but the present invention is not limited to this, and the distance between the members is not limited to this. And can be applied to actuators that control the pressing force (load).

FIG. 18 is a schematic view showing another example of the actuator used in the control method according to the present embodiment. With reference to FIG. 18, the actuator 22 includes a moving member 28 arranged to drive rotationally with respect to the substrate 24. The moving member 28 is rotationally driven by a motor or the like (not shown) to change the relative distance between the moving member 28 and the object 30, and also applies a load from the moving member 28 to the object 30.

By configuring the moving member 28 as a rail or the like for supplying some member, it can be applied to an application for supplying a raw material. Alternatively, by arranging a probe or the like at the tip of the moving member 28, it can be used as an inspection device or the like for detecting an object 30.

Alternatively, by arranging a polishing member or the like at the tip of the moving member 28, it can be used as a polishing device for polishing the surface of the object 30 to be rotationally driven.

As described above, the control method according to the present embodiment includes not only the linearly moving moving member as shown in FIG. 1, but also the rotating moving member as shown in FIG. 18, or yet another arbitrary behavior. It can be applied to the configuration including the moving member shown.

<J. Advantages>
According to the present embodiment, by combining impedance control and speed control or position control other than impedance control, high-speed and highly accurate pressing control can be realized.

Further, according to the present embodiment, the parameter set used for impedance control is prepared separately for the section before and after the moving member comes into contact with the object and the section after that, which is suitable for each aspect. Impedance control can be realized.

Further, according to the present embodiment, when a certain condition is satisfied for the impedance control, the target value is corrected by the correction amount based on the knowledge acquired in advance, so that the moving member comes into contact with the object. The peak of the load can be reduced, and the parameter adjustment for reducing the peak of the load can be facilitated. Further, it is possible to achieve both reduction of the load peak and optimization of the tact time.

It should be considered that the embodiments disclosed this time are exemplary in all respects and not restrictive. The scope of the present invention is shown not by the above description but by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

1 control system, 2,22 actuators, 4 housings, 6 ball screws, 8 nuts, 10 motors, 12 counters, 14 servo drivers, 16 load cells, 28 moving members, 24 base materials, 30 objects, 100 control devices, 102 calculations. Processing unit, 104 functional unit, 110 processor, 112 main memory, 114 secondary storage, 116 user program, 118 sequence program, 120 motion program, 122 system program, 124 bus master circuit, 126 local interface circuit, 128 network master circuit, 152,156,160,162 coefficient calculators, 154,158,164 adders / subtractors, 166 first port, 168 differentiaters, 170 second ports, 180 switches.

Claims (9)

A control device that changes the relative distance between an object and a moving member and controls the magnitude of the load applied from the moving member to the object.
A first control means for sequentially calculating command values for the moving member according to a predetermined speed or position pattern, and
When the predetermined first condition is satisfied, the second control means for sequentially calculating the command value for the moving member according to the control calculation formula corresponding to the impedance control instead of the calculation of the command value by the first control means. equipped with a door,
The first control means sequentially calculates the speed command value for the moving member according to the speed pattern, and then sequentially calculates the speed command value.
Said second control means in accordance with said control arithmetic expression, that to calculate the current speed command value by using the actual speed, the control device. The control device according to claim 1, wherein the control calculation formula corresponding to the impedance control includes a term proportional to the difference between the target value and the actual value for the dimension of the command value. The control device according to claim 2, wherein the control calculation formula corresponding to the impedance control further includes a term proportional to the difference between the target value and the actual value for the dimension in which the command value is integrated. The second control means controls a first period including a time point when the moving member comes into contact with the object according to the impedance control in which the first parameter set is set, and subsequently differs from the first parameter set. The control device according to any one of claims 1 to 3 , wherein the second period following the first period is controlled according to the impedance control in which the second parameter set is set. According to any one of claims 1 to 4 , the target value for calculating the speed command value for the moving member is reduced by the amount of correction acquired in advance before the moving member comes into contact with the object. The control device described. The second control means calculates the speed command value when a predetermined second condition is satisfied in the process of sequentially calculating the command value for the moving member according to the control calculation formula corresponding to the impedance control. The control device according to claim 5 , wherein the target value for the purpose is reduced by the correction amount. The control device according to claim 6 , wherein the second condition includes the lapse of a predetermined time from the start of the impedance control by the second control means. The second condition takes into consideration the peak of the load generated immediately after the moving member comes into contact with the object and the length of time required for a series of processes in which the moving member comes into contact with the object and applies a load. 7. The control device according to claim 7. A control program that changes the relative distance between an object and a moving member and controls the magnitude of the load applied from the moving member to the object. The control program is a speed or a predetermined speed in a computer. The first control step of sequentially calculating the command value for the moving member according to the pattern about the position, and
When the predetermined first condition is satisfied, the second control step of sequentially calculating the command value for the moving member according to the control calculation formula corresponding to the impedance control instead of the calculation of the command value by the first control step. And run ,
The first control step includes a step of sequentially calculating a speed command value for the moving member according to a pattern for speed.
The second control step is a control program including a step of calculating the current speed command value using the actual speed value according to the control calculation formula.