JPH08140386A - Method for estimating inertia of servo motor - Google Patents

Abstract

PURPOSE: To estimate the inertia of a mechanical system including a servo motor accuracy by providing a step for determining the inertia based on a torque required for accelerating/decelerating a determined inertia component and an accelerative/decelerative drive acceleration. CONSTITUTION: At first, a servo motor is driven at a constant speed and a torque required for constant speed operation is measured and then torques F, G required for canceling the frictional component and the gravitational component, respectively, are determined. The servo motor is accelerated and a torque command Tc to be applied is determined and then the time variation of torque T required for acceleration drive is determined. Subsequently, time variation of the acceleration in acceleration drive is determined based on the measurements thus determining the relationship between the speed (v) and the torque T based on the time variation of torque T required for the acceleration drive and the time variation of the speed, and the relationship between the speed (v) and the acceleration A based on the time variation of acceleration. Finally, a torque TJ required for accelerating the inertia is determined according to a formula; TJ=T-F-G, and then it is divided by the acceleration A to determine an inertia J. This method can estimate the inertia accurately.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to control of a servomotor for driving a feed shaft of a machine tool or an arm of a robot, and more particularly to a method of estimating inertia of a mechanical system of the servomotor.

[0002]

2. Description of the Related Art When a feed shaft of a machine tool or an arm of a robot is driven by a servo motor, the servo motor is controlled by a numerical controller. In controlling the servo motor, a control system including a mechanical portion of the servo motor is configured, and each control element is set based on the configuration. In the mechanical element of the servomotor, the control coefficient is set based on the inertia of the motor and mechanical system.

FIG. 9 is a block diagram showing a conventional feed-forward control for a position loop. In FIG. 9, Kp of the transfer function 1 is the position gain in the position loop, K1 of the velocity loop compensator 2 is the integral gain, K2 is the proportional gain, and the transfer function 4
Is a position loop feedforward term, α is a position feedforward coefficient, transfer function 6 is a velocity loop feedforward term, and β is a velocity feedforward coefficient. Further, 3 is a mechanical part of the servo motor, Kt is a torque constant, and Jm is inertia.

In the block diagram, the servomotor is controlled as follows. The difference between the position command output from the numerical controller or the like and the current position of the servo motor detected by the position detector or the like is calculated, and the position deviation is multiplied by the position gain Kp (normally proportional processing is performed) to determine the speed. Call for orders. Next, the position command is differentiated, and the speed command is added to a value obtained by multiplying the position feed-forward coefficient α to form a feed-forward-controlled speed command. The actual speed of the servomotor is subtracted from the speed command to obtain a speed deviation, and the speed deviation is integrated to obtain an integral gain K.
The current command is obtained by adding the value obtained by multiplying 1 and the value obtained by multiplying the velocity deviation by the proportional coefficient K2. Next, the position command is differentiated twice, and the current command is added to a value obtained by multiplying the velocity feedforward coefficient β to form a feedforward-controlled current command. This current command is passed to the mechanical part of the servo motor to drive the servo motor.

The above control improves the response of the control system by position feedforward and velocity feedforward. In order to improve the responsiveness, normally, the velocity feedforward coefficient β is set to a value close to the value of Jm / Kt, and this setting cancels the friction component of the mechanical system by the integrator in the velocity loop compensator, It is intended to form the torque for inertia during acceleration / deceleration by the velocity loop feedforward coefficient β.

Conventionally, the inertia of the motor and mechanical system of this servomotor is calculated by calculation, for example, on the basis of data such as the mass distribution, shape and size of the object.

[0007]

The above-described conventional numerical control system has a problem that the inertia of the motor of the servomotor and the mechanical system cannot be accurately obtained.

In order to obtain the inertia of the motor and the mechanical system of the servo motor by calculation as in the conventional case, the motor and the motor are calculated so that the inertia can be easily calculated on the basis of the data such as the mass distribution, shape and size of the object. The mechanical system is simplified by modeling or the like, and is performed based on the model.

However, in the conventional inertia calculation, an accurate inertia cannot always be obtained due to an error due to the modeling, a displacement during driving of the servo motor, and the like. Due to the inertia error of the motor and the mechanical system, for example, when the feedforward control for the position loop is performed, the velocity feedforward coefficient β does not accurately correspond to the inertia of the motor and the mechanical system. In this case, the torque for inertia during acceleration / deceleration cannot be fully shared by the velocity loop feedforward coefficient β,
The torque for the inertia that could not be shared will be shared by the integrator in the speed loop compensator. Since the response speed of this speed loop compensator is slower than that of the speed loop feedforward, the response in the entire control system is delayed. The response of this control system causes a shape error in the machine tool.

Therefore, an object of the present invention is to solve the above-mentioned conventional problems and provide a method for estimating the inertia of a servo motor which can estimate the inertia of a mechanical system including the servo motor more accurately. To do.

[0011]

According to the present invention, in a method of estimating the inertia of a servo motor, a step of obtaining a torque required to drive the servo motor at a constant speed and a method of accelerating and decelerating the servo motor are provided. Necessary to obtain the required torque, to obtain the torque required to accelerate and decelerate the inertia of the servomotor from the two torques obtained in the previous step, and to accelerate and decelerate the inertia obtained in this step. The above object is achieved by including a step of obtaining an inertia from a large torque and acceleration during acceleration / deceleration driving.

Further, according to the present invention, in the method of estimating the inertia of a servo motor, the servo motor is driven at a plurality of constant speeds, and the relationship between the driving speed of the servo motor and the torque required to drive the servo motor at the speeds. The step of obtaining, the step of accelerating and decelerating the servo motor, the step of obtaining the relationship between the speed during acceleration and deceleration and the torque required to drive at that speed, and the torque required during the acceleration and deceleration, which is necessary at the constant speed A step of obtaining a torque required to accelerate / decelerate the inertia of the servo motor by subtracting the torque, and a step of obtaining an inertia from the torque required to accelerate / decelerate the inertia and the acceleration corresponding to the torque. By providing, the said objective is achieved.

When the object to be driven is driven by the servo motor, the torque generated by the servo motor includes the torque required to accelerate / decelerate the inertia of the motor and the mechanical system and the torque required to move at a constant speed. . Further, the torque required to move at a constant speed includes the torque required to compensate for the friction component and the torque required to compensate for the gravity component when the gravity shaft is included.

The inertia of the motor and the mechanical system can be obtained from the torque and acceleration required to accelerate / decelerate the inertia. Then, the inertia estimation method of the present invention obtains the torque required to accelerate or decelerate the inertia by subtracting the torque required at a constant speed from the torque required at the time of acceleration / deceleration, and divides the torque by the acceleration. It is estimated by that.

In the method of the present invention, the torque for compensating for the friction of the servomotor can be obtained by the torque required to drive the servomotor at a constant speed. The torque for compensating the friction component can be obtained by an average value of the torque required for driving in the same direction as the gravity direction and the torque required for driving in the opposite direction, and for compensating the gravity component of the gravity axis. The torque is
It can be obtained by halving the difference between the torque required for driving in the same direction as the gravity direction and the torque required for driving in the opposite direction. Further, the torque can be obtained from a current command value when driving at a constant speed.

In the method of the present invention, the torque required for accelerating the servo motor can be obtained from the time change of the current command value with respect to the set speed command, and
The acceleration can be obtained from the time change of the feedback speed with respect to the set speed command.

[0017]

According to the present invention, the torque required to drive the servo motor at a constant speed is obtained, the torque required to accelerate / decelerate the servo motor is obtained, and the inertia of the servo motor is calculated from the obtained two torques. When the drive target is driven by the servo motor by obtaining the torque required to accelerate / decelerate the minute and the inertia calculated from the torque required to accelerate / decelerate the obtained inertia and the acceleration during acceleration / deceleration Estimate the inertia of the servo motor.

Further, according to the present invention, the servo motor is driven at a plurality of different constant speeds, the torque required to drive at that speed is obtained from the current command value at that time, and the servo motor in the constant speed drive is obtained. The relationship between the drive speed and the required torque is calculated. If it doesn't have a gravity axis,
The torque for compensating for the friction of the servo motor can be obtained by obtaining the current command for instructing the servo motor in the constant speed drive. Further, in the case of having a gravity axis, if the average value of the torque required for driving in the same direction as the gravity direction and the torque required for driving in the opposite direction is obtained, the torque that compensates for the friction component of the gravity axis can be obtained. It is possible to obtain the torque for compensating for the gravity component of the gravity axis if it is obtained by halving the difference between the torque required for driving in the same direction as the gravity direction and the torque required for driving in the opposite direction.

Next, the servomotor is accelerated / decelerated, and the relationship between the speed during acceleration / deceleration and the torque required to drive at that speed is determined. Then, by subtracting the torque required at a constant speed from the torque required for acceleration / deceleration, the torque required to accelerate / decelerate the inertia of the servo motor can be obtained.

By dividing the torque required for accelerating and decelerating the inertia by the acceleration corresponding to the torque, the inertia of the motor of the servo motor and the mechanical system can be estimated.

[0021]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a flow chart for explaining the steps of the inertia estimation method of the present invention, and FIGS. 2 to 4 are more detailed flow charts during the steps.
5 and 6 are graphs of characteristic values such as torque during each step in the inertia estimation method.

The overall steps of the inertia estimation method of the present invention will be described with reference to the steps S1 to S9 in the flowchart of FIG. 1, and steps S2-1-1 to S2-1 of the flowchart of FIG. The step of obtaining the torque required to cancel the friction component in the case other than the gravity axis is shown by using the code of -7, and in FIG. 3, the code of S2-2-1 to step S2-2-7 is used. In order to cancel the gravitational component in the case of the gravitational axis, the process of obtaining the torque required to cancel the frictional component in the case of the gravitational axis is shown, and in FIG. 4, the symbols of S3-1 to S3-7 are used. The process of obtaining the torque required for is shown.

In the flowchart of FIG. 1, first, the servomotor is driven at a constant speed. This constant speed driving is performed to obtain a torque F for canceling the friction component and a torque G for canceling the gravity component in the following steps S2 and S3 (step S1).

Then, in constant speed driving of this servo motor, the torque required to operate at a constant speed is measured. The torque required to operate at this constant speed does not include the torque required to accelerate or decelerate the servo motor, and is necessary to cancel the friction when the servo motor does not have a gravity axis. The torque is the sum of the torque F required to cancel the friction component and the torque G required to cancel the gravity component when the servomotor has a gravity shaft. Therefore, in step S2, the torque F required to cancel the friction component is obtained, and in step S3 the torque G required to cancel the gravity component is obtained. If the servo motor does not have a gravity axis, only step S2 is performed, and if the servo motor has a gravity axis, steps S2 and S3 are performed.

The process of obtaining the torque required to cancel the frictional component when the servo motor does not have a gravity shaft (the process of step S2-1) will be described with reference to the flowchart of FIG. In order to obtain the torque F required to cancel the friction component, the constant speed vc is set (step S2-1-1), and the speed command value is set by the constant speed vc (step S2-1).
-2), the servo motor is driven by the speed command value to rotate at a constant speed vc (step S2-1-3).
Note that this step S2-1-1 to step S2-1
Step 3 is a step corresponding to step S1.

When a torque command is obtained while the servomotor is rotating at a constant speed vc, the torque F necessary to cancel the friction can be measured, and the measured value is stored (step S2-1
4).

It is judged whether or not the measurement of the torque F is completed at a plurality of constant speeds having different values (step S2-
1-5), constant velocity v if all measurements are not completed
The value of c is changed (step S2-1-6), and steps S2-1-1 to S2-1-4 are repeated again. When the measurement at all measurement points is completed, the relationship between the speed v and the torque F for canceling the friction component can be obtained. FIG. 5 shows the relationship between the speed v and the torque F for canceling the friction component (step S2-
1-6). The curve shown in FIG. 5 can be obtained from the measurement points by, for example, interpolating between the measurement points by spline interpolation or the like.

Next, referring to the flowchart of FIG. 3, in the case where the servomotor has a gravity axis, the step of obtaining the torque required to cancel the friction of the gravity axis (step S2-2) explain. In order to obtain the torque F required to cancel the amount of friction, the moving direction is first set to the up direction (step S2-2-1). In this case, the upward direction is the direction in which the servo motor is driven against gravity, and when the servo motor is moved in the upward direction, the torque required to cancel the friction component and the gravity component are canceled. Therefore, a torque that is the sum of the torque required for In this step, the torque required for canceling the friction component is obtained.

In this upward movement direction, the torque F required to cancel the frictional component is obtained by the same process as in step S2-1 (step S2-2-).
2). Then, the obtained torque F is set as the upward torque Fup (step S2-2-3). This torque Fup is
It can be represented by (torque F + torque G).

Next, the moving direction is set to the down direction (step S2-2-4). In this case, the downward direction is the direction in which the servo motor is driven in the direction in which gravity acts, and when moving the servo motor in the downward direction, the torque and gravity required to cancel the friction component are canceled. Therefore, a torque that is different from the torque required for that is required.

In this downward moving direction, the torque F required to cancel the frictional component is obtained by the same process as in step S2-1 (step S2-2-).
5). Then, the obtained torque F is set to the downward torque Fdow.
n (step S2-2-6). This torque Fdo
wn can be represented by (torque F-torque G).

Letting Fg be the torque F required to cancel the friction in the case of the gravity axis, Fg is (Fup +
Fdown) / 2 (step S2-2-7). Next, a process (process of step S3) of obtaining the torque G required to cancel the gravity component when the servo motor has the gravity shaft will be described with reference to the flowchart of FIG. To obtain the torque G required to cancel the gravity component, in steps S3-1 to S3-6, the step S
Torque F required to cancel the friction of 2-2
(Step S2-2-1 to Step S2-
Similarly to 2-6), the ascending torque Fup and the ascending torque Fdown are obtained.

If the torque required to cancel the gravity component in the case of the gravity axis is G, G is (Fup
-Fdown) / 2 (step S3-7). Therefore, in step S2 and step S3, by the constant speed driving of the servo motor,
A torque F required to cancel the friction component and a torque G required to cancel the gravity component are obtained.

Next, the servo motor is accelerated and driven (step S4). Here, in this acceleration drive, for example, a speed command of a certain set speed value is given to the servomotor in a state of zero speed, and the servomotor is driven until the speed reaches a set speed from zero.

In this acceleration drive, the time change of the torque T required for the acceleration drive is obtained by obtaining the torque command Tc applied to the servo motor. An example of this measurement result is shown in FIG. 6B (step S5). Also, in the same acceleration drive, the time change of the speed in the acceleration drive can be obtained by obtaining the feedback speed v of the servo motor (an example of this measurement result is shown in FIG. 6A). From the result, the time change of the acceleration in the acceleration drive can be obtained (step S6).

Next, the relationship between the speed v and the torque T in the acceleration drive is obtained from the time change of the torque T necessary for the acceleration drive and the time change of the speed in the acceleration drive obtained by the above measurement (this result example is shown). FIG. 6 (c)). Further, the relationship between the speed v and the acceleration A in the acceleration drive is obtained from the time change of the acceleration in the acceleration drive (the result example is shown in FIG. 6D). The relationship between the speed v and the torque T is to obtain the torque TJ required to accelerate the inertia of the servo motor, and the relationship between the speed v and the acceleration A is the acceleration for obtaining the inertia of the servo motor. This is to determine

The torque T required for the acceleration drive obtained in the step S7 is necessary for canceling the torque TJ required for accelerating the inertia and the torque F required for canceling the friction component and the gravity component required for canceling the gravity component. Torque G
Is the sum (T = TJ + F + G), the torque TJ required for accelerating the inertia is the torque F required for canceling the friction component from the torque T required for acceleration driving.
Can be obtained by subtracting the torque G required to cancel the gravity. Therefore, in step S8, the torque TJ necessary for accelerating the inertia is calculated by calculating TJ = TFG.
Ask for. FIG. 6E shows an example of the result of the torque TJ necessary to accelerate this inertia (step S8).

The inertia J of the motor and mechanical system of the servo motor is the torque T required to accelerate the inertia.
It is obtained by the ratio of J and acceleration A (J = TJ / A). According to the relationship of the acceleration A with respect to the speed v shown in (d) of FIG. 6, the acceleration A changes according to the speed v. A change in the acceleration A used for calculating the inertia J affects the value of the inertia J. Therefore, in order to obtain a constant value of the inertia J, a region which is a speed normally used by the servo motor and in which the change in the acceleration A is small is defined in (d) of FIG. 6 and corresponds to the speed v at the acceleration A. Torque TJ
Is calculated in (e) of FIG. 6, and the calculated torque TJ is divided by the acceleration A to calculate the inertia J (= TJ / A) (step S9).

As a result, the torque required to accelerate the inertia of the servo motor and the torque required to cancel the friction component and the gravity component are separated, and the torque required to accelerate the inertia is separated from the servo motor. The inertia of the motor and mechanical system can be estimated.

The measurement error can be reduced by performing the inertia estimation process in the steps S1 to S9 a plurality of times and averaging the obtained plurality of inertia values.

(Example of control device for carrying out embodiment of the present invention)
FIG. 7 is a block diagram of a digital servo control device for carrying out an embodiment of the present invention, and is schematically shown because the configuration is the same as that of a device for performing conventional digital servo control.

In FIG. 7, 10 is a numerical controller (hereinafter referred to as NC), 12 is a shared RAM, 14 is a digital servo circuit having a microcomputer (hereinafter referred to as CPU) configuration, 16 is a servo amplifier such as a transistor inverter, and 18 Is a servo motor, and 20 is a pulse coder that generates a pulse as the servo motor 18 rotates.

The NC 10 has a position command cycle (division cycle) IT
The position command is written in the shared RAM for each P, the CPU of the digital servo circuit 14 reads this position command from the shared RAM, and the position command period ITP is divided into N cycles T.
The position loop process is performed at p (ITP = Tp × N). I
The position command an in the position loop processing Tp is obtained so that the position command output from the NC 10 for each TP cycle is evenly distributed during the ITP cycle, and the servo command of the servo motor 18 obtained by this position command an and the feedback pulse from the pulse coder 20 is obtained. Position loop processing is performed based on the difference from the current position, speed feedforward control processing is performed to obtain a speed command, and then the speed command and the pulse coder 20
A current command is obtained by performing speed loop processing and speed feedforward processing from the actual speed of the servomotor 18 obtained by the feedback pulse from. Then, current loop processing is performed, a PWM command is created, and the servo motor 18 is driven via the servo amplifier 16.

(Example of Control Using Inertia Obtained by the Method of the Present Invention) An example of control of a servo motor using the motor J of the servomotor and mechanical system obtained by the inertia estimating method of the present invention will be described.

FIG. 8 is a block diagram when feedforward control is performed on the position loop as in the case of FIG. In FIG. 8, Kp of the transfer function 1 is the position gain in the position loop, K1 of the velocity loop compensator 2 is the integral gain, K2 is the proportional gain, transfer function 4 is the position loop feedforward term, and α is the position Is a feedforward coefficient of, and the transfer function 6 is a term of the velocity loop feedforward, and β is a velocity feedforward coefficient. Further, 3 is a mechanical part of the servo motor, which is K
t is a torque constant, and Jm is inertia.

In this control block, the velocity feedforward coefficient β is set by the value Jm / Kt obtained by dividing the inertia Jm obtained by the inertia estimation method of the present invention by the torque constant Kt.

The current command value commanded to the servo motor is
As described above, the speed loop compensator 2 is based on the value obtained by subtracting the speed feedback value from the sum of the speed command obtained by multiplying the position gain Kp and the differential value of the position command by the feedforward coefficient α. It is formed by the current command to be formed and the value obtained by multiplying the twice-differential value of the position command by the velocity feedforward coefficient β.

Here, since the feedforward coefficient β of the speed is set to a value based on the inertia Jm, the speed loop feedforward can form a torque corresponding to the inertia amount during acceleration / deceleration, and
The velocity loop compensator can generate a torque that cancels friction and gravity of the mechanical system. Therefore,
Unlike the conventional control, the speed loop compensator does not share a part of the torque corresponding to the inertia during acceleration / deceleration.For the inertia during acceleration / deceleration, a high-speed response is provided in the speed loop feedforward. It can be carried out.

(Effects of the Embodiment) When the value obtained by dividing the inertia obtained by the inertia estimation method of the present invention by the torque constant is used as the velocity loop feedforward coefficient, the inertia portion of the torque of the servo motor is fed to the velocity loop feed. The forward and the friction and the gravity can be shared by the velocity loop compensator.
The torque output from the servomotor can be separated into torque for inertia acceleration and torque for compensating for friction, and high-speed and highly accurate control can be performed. Further, this can reduce the shape error in the case of a machine tool.

[0051]

As described above, according to the present invention,
It is possible to provide a method for estimating the inertia of a servo motor, which can estimate the inertia of the motor and the mechanical system of the servo motor more accurately.

[Brief description of drawings]

FIG. 1 is a flowchart for explaining steps of an inertia estimation method of the present invention.

FIG. 2 is a flowchart for obtaining a torque required to cancel a friction component other than the gravity axis.

FIG. 3 is a flowchart for obtaining a torque required to cancel a friction component of a gravity axis.

FIG. 4 is a flowchart for obtaining a torque required to cancel a gravity component on a gravity axis.

FIG. 5 is a graph showing a torque value required to cancel friction at a constant speed.

FIG. 6 is a graph showing measured values for obtaining a torque required to accelerate inertia.

FIG. 7 is a block diagram of a digital servo control device that implements an embodiment of the present invention.

FIG. 8 is a block diagram in the case where feedforward control is performed on the position loop according to the embodiment of the present invention.

FIG. 9 is a block diagram in the case where feedforward control is performed on a position loop that has been conventionally performed.

[Explanation of symbols]

 1 Position loop transfer function 2 Speed loop compensator 3 Servomotor mechanical part 4 Position loop feedforward term 6 Speed loop feedforward term Kp Position loop position gain K1 Integral gain K2 Proportional gain α Position feedforward coefficient β Velocity feedforward coefficient Kt Torque constant Jm Inertia

Claims (8)

[Claims] 1. In a servo motor, a step of obtaining a torque required to drive the servo motor at a constant speed, a step of obtaining a torque required to accelerate drive the servo motor, and a servo motor from the two torques. And a step of obtaining a torque required for accelerating and decelerating the inertia portion, and a step of obtaining an inertia from the torque required for accelerating and decelerating the inertia portion and the acceleration during acceleration / deceleration driving. Servo motor inertia estimation method. 2. In a servo motor, the step of driving the servo motor at a plurality of different constant speeds to obtain the relationship between the driving speed of the servo motor and the torque required to drive at that speed, and the acceleration / deceleration of the servo motor. The step of driving and obtaining the relationship between the speed during acceleration / deceleration and the torque required to drive at that speed, and the inertia of the servo motor by subtracting the torque required at the constant speed from the torque required at the acceleration / deceleration Servo motor comprising a step of obtaining a torque required to accelerate and decelerate the amount of inertia, and a step of obtaining an inertia from a torque required to accelerate and decelerate the inertia amount and an acceleration corresponding to the torque. Inertia estimation method. 3. The inertia estimation method for a servo motor according to claim 1, wherein the torque for compensating for the friction of the servo motor is obtained from the torque required to drive at the constant speed. 4. The servo according to claim 3, wherein the torque for compensating for the friction component of the gravity shaft of the servomotor is obtained by averaging the torque required for driving in the same direction as the gravity direction and the torque required for driving in the opposite direction. Motor inertia estimation method. 5. The torque for compensating for the gravity component of the gravity axis of the servomotor is determined by one half of the difference between the torque required for driving in the same direction as the gravity direction and the torque required for driving in the opposite direction. 1. A method of estimating inertia of a servo motor according to 1 or 2. 6. The inertia estimation method for a servo motor according to claim 1, wherein the torque required to drive the servo motor at a constant speed is obtained from a current command value during constant speed driving. 7. The method of estimating the inertia of a servo motor according to claim 1, wherein the torque required for accelerating and decelerating the servo motor is obtained from a time change of a current command value with respect to a set speed command. 8. The inertia estimation method for a servo motor according to claim 1, wherein the acceleration is obtained from a time change of a feedback speed with respect to a set speed command.