Position control device

Abstract

Disclosed is a position control device for controlling the position of a control target, which is configured to sequentially calculate a speed command value (V) and a torque command value (tau c) on the basis of a position command value (Posref) and a position detection value (Pos); determining, on the basis of a speed command value (V) calculated from the position command value (Posref), whether the control target is operating at a constant speed in a very low speed region in which the speed of the control target is within a speed range less than or equal to a predefined threshold value (Vth); then, in response to determining that the control target is in very low constant speed operation based on the acceleration command value (A), a friction compensation amount ([tau] s) for compensating for friction generated in the very low constant speed operation is added to at least one of the torque command value ([tau] c), the speed command value (V), and the position command value (Posref).

Description

[0001] Cross-references to related applications

[0002] This application claims priority to Japanese Patent Application No. 2024-083372, filed on May 22, 2024, the entire contents of which (including the description, claims, drawings and abstract) are incorporated herein by reference. Technical Field

[0003] This specification discloses a position control device for, for example, a machine tool. Background Technology

[0004] As an example of a conventional position control device used in machine tools Figure 3 A block diagram corresponding to the position control device disclosed in Patent Document 1 is shown. The following will describe... Figure 3 The diagram illustrates the structure and operation of the position control device 112. The position command value Pos_ref is input from a host device (not shown) to the position control device 112.

[0005] The position command value Pos_ref is differentiated over time by differentiators 101 and 104, and the respective outputs serve as the velocity command value V and the acceleration command value A. The acceleration command value A is amplified by a factor of the acceleration torque conversion constant K by amplifier 105, and the result serves as the acceleration torque command value τaa, used to generate the corresponding acceleration in the target system 110. The velocity command value V and the acceleration torque command value τaa are added to the outputs of the position controller 102 and the speed controller 108, respectively. This processing sequence constitutes a well-known feedforward process aimed at improving the responsiveness of the position detection value Pos to the position command value Pos_ref.

[0006] Subtractor 100 subtracts the position detection value Pos from the position command value Pos_ref to calculate the position deviation Pos_ref - Pos. It should be noted that the position detection value Pos is a position detection signal obtained by detecting the position of the control target of the target system 110 using, for example, a linear scaling method (not shown).

[0007] Position controller 102 amplifies the position deviation [Pos_ref-Pos] proportionally via the position loop gain. In adder 103, the output of position controller 102 is added to the speed command value V and the initiation friction compensation value Vsfc to calculate the final speed command value Vc. Subtractor 107 subtracts the speed detection value Vel, obtained by detecting the speed of the target system 110 (i.e., the control target) using, for example, a linear scaling (not shown), from the final speed command value Vc to calculate the speed deviation [Vc-Vel]. The speed detection value Vel is, for example, the time derivative of the rotational angular position of a position detector coupled to the servo motor within the target system 110, or the output of a speed detector coupled to the servo motor. Speed ​​controller 108 is a typical PI controller, which amplifies the speed deviation [Vc-Vel] via the proportional gain of the speed loop and the integral gain of the speed deviation.

[0008] In adder 109, the output of speed controller 108 is added to the acceleration torque command value τaa, thereby calculating the torque command value τc. The torque command value τc is input to target system 110, causing target system 110 to start operating.

[0009] The following will describe Figure 3 The diagram illustrates an overview of a conventional position control device 112. Friction may be discontinuous at the instants before and after the controlled target begins to move from a stationary state; in other words, at startup. The conventional positioning control device 112 includes a startup friction compensation calculation unit 111 for torque compensation during startup. In response to the detection from the speed command value V that the target system 110 has moved in different directions and entered a stop, causing the direction of movement before the stop to differ from the direction of movement after startup, the startup friction compensation calculation unit 111 generates a friction compensation value Vsfc at startup in a predetermined form based on the torque generated by the starter motor detected from the torque command value τc and the change in friction torque instantaneously after startup, thereby improving tracking characteristics during startup.

[0010] Existing technical documents

[0011] Patent documents

[0012] Patent Document 1: JP 3840429 B Summary of the Invention

[0013] One problem with conventional position control is that when the controlled target decelerates to an extremely low speed and does not come to a complete stop but continues to run at a constant speed in the same direction at an extremely low speed, the position tracking accuracy may drop immediately after the extremely low constant speed operation begins.

[0014] As is well known, the guiding mechanism (e.g., particularly the sliding guiding mechanism) in the target system 110 is assumed to be in a state of boundary lubrication, mixed lubrication, or hydrodynamic lubrication based on the operating speed. As a characteristic of the coefficient of friction that occurs under these conditions, the characteristic represented by the Stribeck curve is widely known, in which large friction is observed in the low-speed region, then temporarily decreases, and then increases again.

[0015] The following description specifically considers the operation of target system 110, which decelerates from the speed region of the hydrodynamic lubrication state and moves after having decelerated to an extremely low speed corresponding to the boundary lubrication region. Because friction acts in the direction of deceleration, the torque command value τc output by position control device 112 during deceleration is less than the drive torque required in the mixed lubrication region. If an attempt is made to transition to extremely low constant speed operation in the boundary lubrication region from this state, the torque will be insufficient because the required torque is greater than that in the hydrodynamic lubrication region. Therefore, position tracking is delayed.

[0016] Figure 4 The diagram illustrates the time waveform of the tracking delay described above. Figure 4 In the example, the speed command value V decreases to a low-speed region at time T1. Starting from time T1, the input speed command value V causes constant speed movement to continue in the same direction while maintaining a low speed without stopping. Figure 4 In the example described above, the phenomenon causes the tracking delay in the position deviation Diff to occur immediately after time T1.

[0017] Patent document 1 discloses a technique for compensation to reduce tracking latency during restart after a stop. However, since the target system 110 does not assume zero speed when transitioning to extremely low speeds, no compensation is performed, resulting in the inability to eliminate the tracking latency described above.

[0018] According to one aspect of this disclosure, a position control device is provided for controlling the position of a controlled target. The position control device is configured to sequentially calculate a speed command value and a torque command value based on a position command value and a position detection value; based on the speed and acceleration of the controlled target calculated from the position command value, determine whether the controlled target is operating at a constant speed in an extremely low speed region, where the speed of the controlled target is within a speed range less than or equal to a predefined threshold, i.e., determine whether the controlled target is currently in "extremely low constant speed operation"; and, in response to determining that the controlled target is in extremely low constant speed operation, add a friction compensation amount for compensating for friction generated during extremely low constant speed operation to at least one of the torque command value, the speed command value, or the position command value.

[0019] The position control device disclosed herein can effectively reduce tracking delay in drive systems where tracking delay caused by friction occurs in extremely low-speed regions. Attached Figure Description

[0020] Embodiments of this disclosure will be described based on the following figures, wherein:

[0021] Figure 1 This is a block diagram illustrating the structure of the position control device.

[0022] Figure 2 The figure shows the time response waveform of the position control device;

[0023] Figure 3 This is a block diagram illustrating a conventional position control device with friction compensation function that operates when the feed axis is actuated; and

[0024] Figure 4 The diagram illustrates the time response waveform according to conventional techniques. Detailed Implementation

[0025] The structure of the position control device will now be described with reference to the accompanying drawings. Figure 1 This is a block diagram illustrating an example structure of a position control device. (Similar to the description above...) Figure 3 Components that are identical in the system are referred to by the same name and are indicated by the same reference numerals, and their descriptions will not be repeated here. Target system 110 is the control target to be controlled by the position control device.

[0026] The friction compensation calculation unit 3 will now be described. The friction compensation timing detection unit 1 and the friction compensation amount generation unit 2 calculate the friction compensation amount τs used to compensate for the tracking delay caused by friction. In the adder 6, the friction compensation amount τs is added to the output of the adder 109 to calculate the torque command value τc.

[0027] The friction compensation timing detection unit 1 determines whether the target system 110 is currently operating at an extremely low constant speed. Specifically, when the absolute value of the speed command value V is less than or equal to a preset speed threshold Vth and greater than zero, the friction compensation timing detection unit 1 determines that the target system 110 is in the extremely low speed region; when the absolute value of the speed command value V is greater than the preset speed threshold Vth, the friction compensation timing detection unit 1 determines that the target system 110 is not in the extremely low speed region. The friction compensation timing detection unit 1 maintains this determination result. The speed threshold Vth defining the extremely low speed region can be set according to, for example, the characteristics of the target system 110 (i.e., the control target). For example, the speed at which the guide mechanism of the control target transitions from a mixed lubrication state to a boundary lubrication state can be set as the speed threshold Vth. Alternatively, the speed threshold Vth can also be the speed at which the guide mechanism of the control target has the minimum coefficient of friction.

[0028] When the target system 110 is in an extremely low-speed region and the acceleration command value A is zero, and a preset time period or longer has elapsed, the friction compensation timing detection unit 1 determines that the target system 110 is operating at an extremely low constant speed. The friction compensation timing detection unit 1 outputs a friction compensation trigger signal Tr. Because it is operating at an extremely low constant speed, the friction compensation trigger signal Tr has the same sign as the speed command value V and an absolute value of 1. Conversely, in response to not operating at an extremely low constant speed, the friction compensation trigger signal Tr is assumed to be zero. To determine whether the acceleration command value A is zero, it can be determined when the acceleration command value A is exactly zero, or alternatively, it should be understood that it can also be determined to be zero when the acceleration command value A is close to zero, i.e., for example, when the absolute value of the acceleration command value A is less than or equal to a predetermined value. It should be noted that since no reverse movement occurs when the target system 110 is in an extremely low-speed region and the acceleration command value A is zero, the function implemented in this disclosure does not rely on a compensation function for compensating for tracking delays during reverse movement.

[0029] Assuming the time point at which the friction compensation trigger signal Tr changes from zero to 1 or -1 is time t = 0, then the friction compensation generation unit 2 outputs the friction compensation amount τs according to formula (1):

[0030] τs(t)=Tr × τca × exp(-t ÷ Td).....(1)

[0031] In formula (1), the compensation magnitude τca and the compensation time constant Td are both predefined coefficients. For example, the compensation magnitude τca can be determined in advance through experiments or simulations. For example, after starting extremely low constant speed operation with friction compensation τs = 0 (i.e., Figure 4 In the context of time T3, the torque command value τc at the point where the position deviation Diff transitions from an upward trend to a downward trend can be set as the compensation magnitude τca. Alternatively, the compensation magnitude τca can be determined by changing the compensation magnitude τca to reduce the cumulative value of the position deviation Diff generated up to the point where the position deviation Diff transitions from an upward trend to a downward trend. Alternatively, the compensation magnitude τca can be selected based on the Stribeck characteristics of the control target, identifying the torque command value that matches the friction generated at a speed equal to the speed threshold Vth (i.e., a reference speed below which is determined to be in the extremely low speed region).

[0032] The compensation time constant Td can also be determined in advance through experiments or simulations. For example, for the compensation time constant Td, extremely low constant speed operation can be performed in advance, and the time elapsed from the start of the extremely low constant speed operation until the point when the position deviation Diff changes from an upward trend to a downward trend can be calculated. Figure 4 T3-T1 in the equation is set as the compensation time constant Td. Alternatively, the compensation time constant Td can be determined by searching for the cumulative value of the position deviation Diff generated at the point in time when the position deviation Diff changes from an upward trend to a downward trend. In either case, according to formula (1), the friction compensation amount τs is assumed to be a large value at the instant of the start of extremely low constant speed operation, and then decreases sharply over time. This allows for appropriate compensation for insufficient torque immediately after the start of extremely low constant speed operation, thereby effectively preventing tracking delay.

[0033] It should be noted that although the friction compensation amount τs is output according to formula (1) in the example described above, the output form can be changed as needed, as long as a friction compensation amount τs suitable for the characteristics of the target system 110 is obtained. For example, the friction compensation amount τs can be a pulse signal. Alternatively, the friction compensation amount τs can be stored in advance in the form of a table or map, with each elapsed time corresponding to a value, instead of calculating the friction compensation amount τs using a formula, thereby identifying the friction compensation amount τs from the table or map.

[0034] Figure 2 The illustration shows the time response of the example described above. For example... Figure 2 As illustrated, target system 110 initially moves at a constant speed, begins to decelerate at time T0, and then operates at an extremely low constant speed starting at time T1. In the example described above, at time T1, the speed of target system 110 is detected to be in the extremely low speed region, and a time interval has elapsed since the acceleration command value A was zero—that is, the time point from the start of compensation. At this point, the friction compensation trigger signal Tr (not shown) becomes 1, causing compensation to begin. Thus, at time T2, the friction compensation amount τs is added to the direct torque command value τc, resulting in a decrease in the position deviation Diff. Figure 2 In the diagram, the diff indicated by the dashed line is... Figure 4 The diagram shows the response waveform in a conventional technique.

[0035] It should be understood that in the example described above, Figure 1 The structure shown in the diagram does not define the order of calculations, but the order can be rearranged as needed, for example, by switching the calculation order of adder 6 and adder 109 or integrating them into a single calculation unit.

[0036] It should also be understood that the position control device is not limited to Figure 1The feedback control system can be, for example, a feedback control system operating in a state feedback manner, where speed and position are fed back to a single controller.

[0037] The position control device structure described above can be used not only for machine tool controllers, but also for various types of industrial machines, such as robots or other industrial machines, that have a drive shaft driven by an electric motor and subject to friction.

[0038] Figure 1 The illustrated position control device can be a computer that physically includes a processor and memory and performs various different operations. For example, the position control device can be implemented by using a central processing unit (CPU) included in the position control device to execute various types of software stored in a storage device. Alternatively, the position control device can also be implemented by a structure mainly composed of hardware including a field-programmable gate array (FPGA). The target system 110 (i.e., the control target) in this document includes, for example, a motor, a driver driven by the motor, an inverter for applying power to the motor according to a torque command value τc, and a position sensor for detecting the position of either or both of the motor and the driver.

[0039] In the example described above, although the friction compensation amount τs output from friction compensation amount generation unit 2 is added to the torque command value τc, an equivalent function can also be provided, for example, by replacing the addition of the integral result of the friction compensation amount τs to the velocity command value V. Similarly, an equivalent function can be provided by adding the double integral result of the friction compensation amount τs to the position command value Pos_ref.

[0040] Reference Symbol List

[0041] 1 Friction Compensation Timing Detection Unit

[0042] 2 Friction Compensation Amount Generation Unit

[0043] 3 Friction Compensation Calculation Unit

[0044] 4. Position control device

[0045] 100, 107 subtractors

[0046] 101, 104 Differentiators

[0047] 102 Position Controller

[0048] 105 amplifier

[0049] 108 Speed ​​Controller

[0050] Adders with capacities of 6, 103, 106, and 109

[0051] 110 Target System

[0052] 111 Start the friction compensation calculation unit

[0053] 112 Position control device

Claims

1. A position control device for controlling the position of a control target, the position control device being configured to: The speed command value and torque command value are calculated sequentially based on the position command value and the position detection value; Based on the speed and acceleration of the control target calculated from the position command value, it is determined whether the control target is running at a constant speed in an extremely low speed region, where the speed of the control target is within a speed range less than or equal to a predefined threshold. as well as In response to determining that the control target is operating at an extremely low constant speed, a friction compensation amount for compensating for friction generated during the extremely low constant speed operation is added to at least one of the torque command value, the speed command value, and the position command value.

2. The position control device according to claim 1, wherein, The friction compensation amount is a signed value that has an absolute value that decreases over time from a predefined compensation amount range, and the sign is the same as that of the speed command value.

3. The position control device according to claim 2, wherein, The position control device is configured to calculate the friction compensation amount according to formula (1): τs(t)=Tr×τca×exp(-t÷Td).....(1) Where Tr represents a constant, which is 1 when the speed command value is positive or -1 when the speed command value is negative; τca represents the compensation amount amplitude; Td represents the compensation time constant; and t represents the time elapsed after the start of the extremely low constant speed operation.

4. The position control device according to claim 2, wherein, The compensation amount is determined based on the Stribek characteristics of the control target as a torque command value that matches the friction generated at a speed threshold, below which the speed of the control target is determined in the extremely low speed region.

5. The position control device according to claim 3, wherein, The compensation magnitude and the compensation time constant are the torque command value and the elapsed time obtained at the point when the position deviation changes from an upward trend to a downward trend after the start of extremely low constant speed operation, under the condition that the friction compensation is zero.

6. The position control device according to claim 3, wherein, The compensation magnitude and the compensation time constant are values ​​obtained by searching for a reduction in the cumulative value of the position deviation generated after the start of the extremely low constant speed operation until the point when the position deviation changes from an upward trend to a downward trend.

7. A method for controlling the position of a control target, the method comprising: The speed command value and torque command value are calculated sequentially based on the position command value and the position detection value; Based on the speed and acceleration of the control target calculated from the position command value, it is determined whether the control target is running at a constant speed in an extremely low speed region, where the speed of the control target is within a speed range less than or equal to a predefined threshold. as well as In response to determining that the control target is operating at an extremely low constant speed, a friction compensation amount for compensating for friction generated during the extremely low constant speed operation is added to at least one of the torque command value, the speed command value, and the position command value.

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