JP7532074B2 - Motor Control Device - Google Patents

Description

The present invention relates to a motor control device for pressing control.

In a spot welding servo gun, the workpiece is clamped with the welding tips of the electrode part of the welding gun, pressure is applied by controlling the torque of the motor, and electricity is passed between the electrode tips to weld the workpiece. With this type of welding gun, the gun moves using position and speed control until it is close to contacting the workpiece, and then switches to torque control to apply pressure. Torque control with a speed limiting function is implemented so that excessive speeds do not occur when switching to torque control, preventing collision with the workpiece. Once welding is complete, movement is resumed using position and speed control.

Patent Document 1 is an example of implementing pressing control by switching between such position control, speed control, and torque control. Patent Document 1 describes a motor control device that controls a motor equipped with an encoder, which includes a position command generation unit that generates a position command, which is a command value for when a mechanical load driven by the motor approaches a pressurized object and the final position of the mechanical load is a certain distance before the pressurized object, a position control unit that outputs a first speed command so that the position of the motor detected by the encoder follows the position command, a pressure command generation unit that generates a pressure command, which is a command value for the pressure or force to be applied to the pressurized object, and a second speed command generation unit that outputs a second speed command so that the pressure or force detected by the mechanical load follows the pressure command when the mechanical load is pressed against the pressurized object. The motor control device is characterized in that it includes a pressure control unit that outputs a creep speed that specifies the upper limit of the motor speed when the mechanical load contacts the pressurized object, a speed command selection unit that selects one of a first speed command and a second speed command and outputs it as the speed command at which the motor should operate, and a speed control unit that outputs a current command that supplies current to the motor so that the motor speed follows the speed command output by the speed command selection unit, and that after selecting the first speed command, the speed command selection unit selects the second speed command or a smaller value of the creep speed after the timing at which the first speed command falls below the creep speed.

In this way, in the method of Patent Document 1, after the timing when the first speed command falls below the creep speed, a process is performed to select the second speed command or a smaller value of the creep speed. However, a pressure detector or force detector is required to configure the pressure control unit, and there is a problem that pressing control cannot be performed in equipment that does not have such detectors. In addition, if there is noise contained in the output of the pressure or force detector, or an unstable element caused by the rigidity of the machine that configures the pressure control loop, a ripple occurs in the speed command from the pressure control unit, and the pressure control loop is interrupted and then restored near the point where the creep speed and the second speed command switch, resulting in an unstable operation.

Patent No. 6113378

The present invention was made to solve the above problems, and its purpose is to provide a control device for a motor for pressing control that does not require a pressure detector or force detector, can quickly transition from position control or speed control to torque control with a speed limiting function, and can quickly and stably transition from a speed-limited state to torque control.

According to one aspect of the present invention, there is provided a motor control device that controls a motor based on a control mode command of either torque or position, and in a position control mode, the motor position is controlled in accordance with a position command, and in the torque control mode, the speed is limited in accordance with a speed limit command at speeds equal to or greater than a speed limit command, and the torque of the motor is controlled in accordance with a torque command at speeds lower than the speed limit command. The motor control device includes a speed detection unit that detects the speed of the motor, a subtractor that subtracts a position from a position command to obtain a position deviation, a position controller that obtains a speed command based on the position deviation, a speed deviation calculator that obtains a speed deviation based on a torque command, an adder that adds the speed deviation based on a torque command and the speed to obtain a speed command based on a torque command, a speed limit unit that limits the speed command based on the torque command based on a speed limit command and outputs the limited speed command, and a speed limiting unit that outputs the speed command based on the control mode automatic switching signal, and A motor control device is provided that includes a speed command selection unit that switches between the speed command from the position controller and the limited speed command to output a motor speed command, a subtractor that subtracts the motor speed from the motor speed command to output a speed deviation, a speed controller that performs a speed control calculation using the speed deviation as an input and outputs a motor torque command, and a motor torque control unit that outputs a torque based on the motor torque command, and the speed controller has a proportional controller and an integral controller, and the speed command selection unit compares the speed command from the position controller with the limited speed command based on the torque command, and selects the value of the speed command from the position controller if the value of the speed command from the position controller is greater than the value of the limited speed command, and selects the value of the limited speed command if the value of the speed command from the position controller is equal to or less than the value of the limited speed command, thereby determining a motor speed command.

The speed command selection unit may enable automatic control mode switching when the position of the member driven by the motor reaches a specified position close to the object of pressing control.

It is preferable that the speed controller selects the limited speed command in the speed command selection unit, and performs proportional control if the speed command based on the torque command is not speed-limited in the speed limiting unit, and performs proportional-integral control if the speed command based on the torque command is speed-limited in the speed limiting unit.

According to the present invention, a pressure detector or a force detector is not required, and a transition from position control or speed control to torque control with a speed limiting function can be performed quickly.
Furthermore, it is possible to provide a control device for a motor used for press-fit control, which is capable of quickly and stably transitioning from a speed limited state to torque control.

FIG. 1 is a block diagram illustrating one aspect of a motor control device and method. FIG. 2 is a diagram showing a specific example of the configuration of the speed controller. FIG. 3 is a diagram showing the results of a simulation in which the actuator moves to a position just before contacting the pressure target under position control, and then the actuator is switched to torque control to perform a pressure application operation.

The following describes in detail the embodiments of the motor control device and method according to the present invention with reference to the drawings. Note that the scope of the present invention is not limited by the description of the embodiments, and any embodiment is included in the scope of the present invention as long as it falls within the technical scope of the invention according to each claim of the claims.
FIG. 1 illustrates one embodiment of a motor control device and method.

As described in the Background Art section above, torque control devices and control methods with a motor speed limiting function based on a torque command and a speed limiting command are well known, so detailed explanations will be omitted, but the present invention can be implemented as follows.

The motor control device A of the present invention, which controls the motor torque and position of the motor 21, is roughly composed of an encoder EN 23, a speed detection unit 25 that determines the speed by differentiating the position of the encoder EN 23, a speed deviation calculator 1, an adder 3, a speed limiting unit 5, a control mode switching unit 7, a subtractor 11, a speed controller 15, a speed command selection unit 16, a motor torque controller 17, and a position controller 35.

The embodiment shown in Fig. 1 shows an example in which a torque control mode and a position control mode can be switched. The functions of each part of the motor control device A are as follows. A torque command _TC is passed through a speed deviation calculator 1 to obtain a speed deviation _SDT based on the torque command. The speed deviation _SDT based on the torque command and a speed V are added by an adder 3 to obtain a speed command _STC based on the torque command. A speed limiting part 5 limits the speed command _STC based on the torque command _TC with a speed limit value commanded by a speed limiting command _SLC to obtain a speed command _SCL after the limiting.
Moreover, the position P is subtracted from the position command _LC to obtain a position deviation _PDT , which is passed to the position controller 35 to obtain a speed command _SC from the position controller.

The control mode switching unit 7 switches between the speed command _SC from the position controller and the limited speed command _SCL based on the speed command selection command _STS from the speed command selection unit 16 to determine the motor speed command _SMC . When the speed command selection command _STS is the speed command from the position controller, the speed command _SC from the position controller is used as the motor speed command _SMC , and when the speed command selection command _STS is the limited speed command _SCL , the limited speed command _SCL is used as the motor speed command _SMC . Then, the motor speed is controlled based on the motor speed command _SMC .

When the motor 21 approaches the object of press-fit control, the upper controller activates the control mode automatic switching signal _CMS based on the position signal, etc. When the control mode automatic switching signal _CMS becomes effective, the speed command selector 16 compares the speed command _SC from the position controller with the limited speed command _SCL , and selects the speed command _SC from the position controller if the speed command _SC from the position controller is greater than the limited speed command _SCL , and selects the limited speed command _SCL if the speed command _SC from the position controller is equal to or less than the limited speed command _SCL to obtain the motor speed command _SMC . The speed of the motor 21 is controlled based on this motor speed command _SMC .

Specifically, the speed is obtained by differentiating the position of the encoder EN23 attached to the motor. The speed is subtracted from the motor speed command _SMC to obtain a speed deviation _SD , which is then passed through the speed controller 15 to calculate the motor torque command _TMT . Based on the motor torque command _TMT , the motor torque controller 17 outputs torque according to the motor torque command _TMT from the motor. The position rotated by the torque output from the motor is detected by the encoder EN23, and the speed is controlled so as to match the motor speed command _SMC .

The speed controller 15 has a proportional controller 15a, and operates only the proportional controller 15a or both the proportional controller 15a and the integral controller 15b depending on a speed controller control signal _STSS from a speed command selection unit 16 based on the control state.
When the speed command selection unit 16 selects the speed command S _C from the position controller, both the proportional controller 15 a and the integral controller 15 b are operated by the speed controller control signal S _TSS to perform proportional-integral control. When the speed command selection unit 16 selects the limited speed command S _CL and the speed command based on the torque command _TC is speed limited, proportional-integral control is performed in the same manner. When the speed command selection unit 16 selects the limited speed command S _CL and the speed command based on the torque command _TC is not speed limited, proportional control is performed by the speed controller control signal S _TSS .

Figure 2 shows a more specific example of the configuration of the speed controller 15 in Figure 1. The proportional controller 15a is configured with the proportional gain 15a-1, and the integral controller 15b is configured with the integral gain 15b-1, the integrator 15b-2, the integral attenuation gain 15b-3, and the changeover switch 15b-4.

When the speed controller 15 is operated with proportional-integral control, the changeover switch 15b-4 is set to 1, causing the integral controller 15b to perform integral operation. When the speed controller 15 is operated with proportional control, the changeover switch 15b-4 is set to 2, the value of the integrator 15b-2 is attenuated to 0 based on an integral attenuation gain with a negative sign, and proportional operation is performed. Each of these parts that perform motor control can be configured with software, and control calculations are performed for each control sample.

When the position of the member driven by the motor 21 reaches a predetermined position close to the object of the pressing control, the speed command selection unit 16 receives the automatic control mode switching signal _CMS and enables automatic control mode switching, i.e., makes the state in which automatic switching between the position control mode and the torque control mode is possible.
The speed command selection unit 16 compares the speed command S _C from the position controller with the limited speed command S _CL .
When the value of the speed command S _C from the position controller is larger than the value of the limited speed command S _CL , the value of the speed command S _C from the position controller is selected.

On the other hand, when the value of the speed command _SC from the position controller is equal to or smaller than the limited speed command value _SCL , the limited speed command value _SCL is selected to determine the motor speed command _SMC .

The speed controller 15 selects the limited speed command in a speed command selection section 16, and if the speed command S _TC based on the torque command _TC has not been limited in the speed limiting section 5, proportional control is performed.
On the other hand, when the speed command _STC based on the torque command is limited by the speed limiting section 5, proportional-integral control is performed.

When the speed command selection command _STS is the limited speed command _SCL , the control mode switching unit 7 selects the limited speed command _SCL , and torque control with a speed limiting function is performed as follows.
If the speed controller 15 is configured with a proportional controller 15a and its gain is GP, then by inverse calculation of the calculation for calculating the motor torque command _TMT from the motor speed command _SMC in the speed control system, the speed command _STC based on the torque command can be calculated from the torque command _TC as follows:

Speed deviation based on torque command S _DT =torque command T _C /GP (1)
Speed command based on torque command S _TC = Speed deviation based on torque command S _DT + Speed V (2)

Then, the speed command _STC based on the obtained torque command is subjected to speed limitation based on the speed limit command _SLC to obtain the limited speed command _SCL .
When the speed control of the motor 21 is performed in accordance with the limited speed command _SCL , the following occurs.
Motor torque command T _MT = speed deviation S _D ×GP = (motor speed command S _MC - speed V) × GP

Here, when the speed limit is not reached, the motor speed command S _MC =the speed command S _TC based on the torque command, so
Motor torque command T _MT =(speed command S _TC based on torque command−speed V)×GP={(speed deviation S _DT based on torque command+speed V)−speed V}×GP (3)
Here, (speed deviation _SDT based on torque command) x GP = torque command/GP x GP = torque command _TC , and the motor torque command _TMT coincides with the torque command _TC . Torque control is performed based on this motor torque command _TMT , and motor torque according to the motor torque command _TMT is output from the motor 21.
When the speed limit is reached, the motor speed command _SMC becomes a speed limit command _SLC , and the motor speed is controlled based on the speed limit command _SLC , and the speed is proportional-integral controlled to the speed limit command _SLC .

Figure 3 shows an example of a simulation result (A to G) when the position control according to this embodiment is used to move the gun to the point where it comes into contact with the object to be pressed, and then the control is switched to torque control to perform the pressing operation. Here, the form when used in a spot welding servo gun is shown as an example.

Waveform A shows the speed command _STC from the position controller.
Waveform B shows the torque command _TC and the load torque.
Waveform C illustrates automatic control (position, torque) mode switching.
A waveform D shows the speed command _SCL after the limit.
Waveform E shows the motor speed command _SMC .
The waveform F represents the velocity V.
Waveform G shows the motor torque command _TMC .

In position control, when the position of the servo gun approaches the pressurized object, automatic control mode switching becomes effective (waveform C). When the speed command S _TC (waveform A) from the position controller becomes equal to or lower than the limited speed command S _CL (waveform D), the speed command selection unit 16 selects the limited speed command S _CL , and the motor speed command S _MC becomes the speed limit value (300 min ^-1 ) set by the speed limit command S _LC (see 0.12-0.14 in waveform E).

Then, the motor approaches the object to be pressurized at a limited speed, and when it comes into contact with the object, the load torque increases (waveform B), the speed decreases (waveform F), the speed limit state is released, and the object is pressurized with the motor torque command _TMT in accordance with the torque command _TC (waveform G).
When the object to be pressed is pressed, the automatic control mode switching is disabled (waveform C). Because there is no pressure control loop, the speed command S _LC after limiting, which is the output from the torque control system with speed limiting function (waveform D), is a constant, clean value, and the switching from position control to torque control is fast and smooth (waveform G). Furthermore, when the speed limiting state is switched to torque control upon contact with the object to be pressed, no unstable phenomena such as chattering are observed, and the control is instantly switched to torque control (waveform G).

As described above, in the present invention, normal position control is performed until the motor approaches the object of press-fit control, and when the motor approaches the object of press-fit control, automatic control mode switching is enabled. When automatic control mode switching is enabled, the speed command selection unit compares the speed command from the position controller with the speed command after limit. When the speed command from the position controller becomes equal to or lower than the speed command after limit, the speed command after limit is selected and torque control with speed limit function is performed. Since there is no pressure control loop in the present invention, switching is fast and smooth, and after switching, the motor operates at the speed limit value until it comes into contact with the pressurized object. When it comes into contact with the pressurized object, the speed decreases and the speed limit state is released. Then, the motor torque command becomes as per the torque command, and the pressurized object is pressurized by the torque command. Switching from the speed limit state to the torque control state is also fast and smooth because there is no pressure control loop, and is automatically switched in the torque control with speed limit function of this control method. The torque control system with speed limit function simply adds the speed to the speed deviation based on the torque command to limit the speed. Therefore, there is no pressure control loop to realize a speed limit above the speed control loop, and no special control parameters are required. Even if the gain of the speed controller is low, when the speed limit is not reached, the motor torque command is calculated according to the torque command and is not affected by the gain of the speed controller. The gain of the speed controller can be adjusted so that the speed loop is stable when controlling the motor speed normally. Also, if there is resonance in the mechanical system, a notch filter or low-pass filter can be provided at the output of the speed controller. In that case, the response to the torque command will decrease by the amount of the filter added.

As described above, in the present invention, a speed command based on a torque command is calculated based on the torque command, a speed limit is performed to obtain a speed command after the limit, the speed command from the position controller is compared with the speed command after the limit, and if the speed command from the position controller is greater than the speed command after the limit, the speed command from the position controller is selected. If the speed command from the position controller is equal to or less than the speed command after the limit, the speed command after the limit is selected, and a motor speed command is obtained to realize press-fit control. This makes it possible to provide a motor control device for press-fit control that does not require a pressure detector or force detector, has a high-speed transition from position control or speed control to torque control with a speed limit function, and has a high-speed and stable transition from a speed-limited state to torque control.

Each of the above-mentioned aspects represents one aspect of the present invention, and the present invention itself is not limited to the specific configurations represented by those aspects. The scope of the present invention includes everything that a person skilled in the art could imagine based on the matters described in the claims.

A Motor control device P Position V Speed 1 Speed deviation calculator 3 Adder 5 Speed limiting section 7 Control mode switching section 11 Subtractor 15 Speed controller 15a Proportional controller 15a-1 Proportional gain 15b Integral controller 15b-2 Integrator 15b-3 Damping gain 15b-4 Changeover switch 16 Speed command selection section 17 Motor torque controller 21 Motor 23 Encoder 35 Position controller L _C position command P _DT position deviation S _C speed command S _CL speed command after limit S _TSS speed controller control signal S _D speed deviation S Speed deviation based on _DT torque command S _LC speed limit command S Speed command based on _TC torque command S _TS speed control device control signal S _MC motor speed command T _C torque command T _MT motor torque command

Claims (3)

A motor control device controls a motor based on a control mode command of either a given torque or a position, the motor control device controls a position of the motor in accordance with a given position command in a position control mode, and limits a speed in accordance with a speed limit command at a speed equal to or higher than a speed limit command in the torque control mode, and controls a torque of the motor in accordance with a given torque command at a speed lower than the speed limit command,
The motor control device includes:
a speed detection unit for detecting a speed of the motor;
a subtractor for subtracting the position of the motor from a position command to obtain a position deviation;
a position controller for determining a motor speed command based on the position deviation;
a subtractor that subtracts the motor speed from the motor speed command and outputs a speed deviation;
a speed controller that performs a speed control calculation using the speed deviation as an input and outputs a motor torque command;
a speed deviation calculator for calculating a speed deviation based on the torque command;
an adder that adds the speed deviation based on the torque command and the motor speed to obtain a speed command based on the torque command;
a speed limiting unit that limits a speed command based on the torque command based on a speed limiting command and outputs the limited speed command;
a speed command selection unit that switches between the speed command from the position controller and the limited speed command based on a control mode automatic switching signal and outputs a motor speed command;
a motor torque control unit that outputs a torque based on the motor torque command,
The speed controller includes a proportional controller and an integral controller.
The speed command selection unit
A motor control device which compares a speed command from the position controller with the limited speed command based on the torque command, and selects the value of the speed command from the position controller if the value of the speed command from the position controller is greater than the value of the limited speed command, and selects the value of the limited speed command if the value of the speed command from the position controller is equal to or less than the value of the limited speed command, thereby determining a motor speed command. 2. The motor control device according to claim 1, wherein the speed command selection unit enables automatic control mode switching when a position of a member driven by the motor approaches an object of press-contact control and reaches a predetermined position. The speed controller includes:
The speed command selection unit selects the limited speed command,
When the speed command based on the torque command is not limited by the speed limiting unit, proportional control is performed.
3. The motor control device according to claim 1, wherein when the speed command based on the torque command is speed-limited by the speed limiting section, proportional-integral control is performed.

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