JPH10254548A - Position control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a position control system capable of absorbing lost motion and performing accurate position control. SOLUTION: This system is provided with an AC signal generation means 7 for generating AC signals provided with the amplitude of a prescribed size in the case that the absolute value of a torque command value is small and reducing the size of the AC signals in the case that the absolute value of the torque command value is large, the AC signals Tadd generated from there are added to the torque command value Tcom obtained from a position command value Xcom and an added torque command value Tcom1 is generated. Current command values Iucom, Ivcom and Iwcom are generated by a three- phase division means 6 from the Tcom1. Thus, the lost motion is absorbed and the oscillation of an electric motor and the resonance of a machine system are prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position control system for controlling rotation of a motor.

[0002]

2. Description of the Related Art In a machine tool or the like, a control device for controlling the rotation of an electric motor installed on a feed shaft or the like so that a desired speed, position, and the like can be obtained is known. These control the position, speed, current and the like as described below. Note that the control of the position, speed, current, and the like performed by the control device is hereinafter referred to as a series of controls. FIG. 7 is a diagram showing an example of a series of controls in a conventional control device. In FIG. 7, the control device normally receives the position command value Xcom from the NC device and the position detection value Xmes and the speed detection value Vmes from the position detection device. The first comparator 1 calculates a difference between the position command value Xcom and the position detection value Xmes, and sets the difference as a position error Xdiff. The position error Xdiff is multiplied by the position loop gain 2 to generate a speed command value Vcom, and the second comparator 3 calculates the difference between the speed command value Vcom and the speed detection value Vmes to calculate the speed error Vcom.
generate diff. Further, Vdiff is multiplied by the speed loop gain 4 to form a torque command value Tcom. Then, in the three-phase dividing means 6, the three-phase current commands Iucom, Ivcom, Iwcom based on the position detection value Xmes.
, And a current amplified by an inverter (not shown) is supplied to the motor.

[0003]

The shaft of the electric motor rotates,
When operating a load to be driven, which is connected in some way to the shaft of the electric motor, there are various ways to connect the shaft and the load. For example, a belt, a pulley, a gear, a ball screw, and the like are conceivable. When gear driving is performed, the following may be considered. As is well known, the gear drive is widely used because of its excellent force transmission efficiency and excellent maintainability. Here, FIG. 8 shows an example of a coupling portion in gear driving. As shown in FIG. 8, between the first gear portion 10 and the second gear portion 11 engaged with each other at the time of gear driving, the tooth surfaces are configured so as not to contact both sides at the same time. Here, the first gear unit 10 is on the motor side,
The second gear unit 11 is on the side to be driven by the electric motor. Between the first gear portion 10 and the second gear portion 11, there is a mechanical play indicated by BR in the figure. This is commonly referred to as backlash. It is known that this backlash is always required when gears are driven. However, if the backlash becomes unnecessarily large, there is an adverse effect due to this. For example, when turning the tool post on a lathe of a machine tool by a synchronous motor, the gear drive is usually performed at a reduced speed so that the load inertia of the tool post is not as large as possible with respect to the inertia of the motor. Therefore, when the reduction ratio is reduced, the load inertia becomes larger than the inertia of the synchronous motor. In such a case, the disturbance received by the motor from the load becomes particularly large, so that the control of the motor becomes unstable. That is, during normal operation, the direction of torque generation of the electric motor is reversed during rotation, but in this case, teeth of the gear collide with each other. Since the tooth-to-teeth collision means that a very large inertia load collides with the electric motor as described above,
The control of the motor becomes very unstable, and the motor that has been subjected to the collision of the very large inertia may oscillate.

The backlash has been described above. This is one of the so-called mechanical dead zones in which no load is applied despite the rotation of the electric motor. Causes of the dead zone include, besides the backlash, which is a play in a mechanical system, various things such as a particularly large deflection when driving a ball screw and a particularly large extension of a belt or pulley when driving a belt or pulley. The description of each of them is publicly known and thus will be omitted. The backlash, deflection, and the like that cause the dead zone are collectively referred to as lost motion. Here, the lost motion amount will be described below with reference to FIG. FIG. 9 is a diagram of a hysteresis curve of a mechanical system for explaining a lost motion amount. In the figure, the horizontal axis represents the operation amount of the motor shaft, and the vertical axis represents the operation amount of the load. When the electric motor and the load are driven from a certain state, the operation starts from a point 0 in the drawing. The load starts operating at the point C due to the lost motion, and thereafter the load operates as much as the operation amount of the motor. When the load is reversed at the point A, the load does not operate again for a while due to the lost motion, and thereafter the same operation is repeated. Here, the point at which the transition from the dead zone to the start of the operation is drawn as a gentle curve is due to the fact that factors such as deflection and elongation are gradually eliminated. The hysteresis curve of FIG. 9 has been described above. Among them, the lost motion amount is the hysteresis amount of the hysteresis curve and is indicated by the amount LM in the figure, and can be obtained by measuring this. However, one side of LM is an intersection of a straight line extending from point A and a straight line extending from point B. The above is the description of the hysteresis curve and the lost motion amount of the mechanical system.

[0005] The dead zone of the mechanical system due to lost motion, including the above-mentioned adverse effects due to backlash, greatly affects the control of the motor, and may cause not only an increase in rotation error of the motor but also oscillation. As described above, in the prior art, there is a problem that a rotation error of the electric motor is large and oscillation easily occurs in a mechanical system having large lost motions such as backlash and deflection. The present invention has been made in view of the above problems, and has as its object to provide a position control system that can perform accurate position control by absorbing lost motion.

[0006]

In order to solve the above-mentioned problems, in a position control system according to the present invention, when the absolute value of a torque command value is small, an AC signal of a predetermined magnitude is generated, An AC signal generating means for reducing the magnitude of the AC signal when the absolute value of the command value is large is provided. A measuring means for measuring a hysteresis amount indicating a behavior of the machine axis with respect to a behavior of the motor axis; and an AC signal setting means for setting an amplitude or a period of the AC signal from an output of the measuring means. It is also preferable that the setting is made so as not to be near the resonance frequency of the mechanical system. As described above, the electric motor can be controlled so as to absorb the lost motion of the mechanical system, and the oscillation of the electric motor and the resonance of the mechanical system do not occur.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments according to the present invention will be described below with reference to the drawings. In FIGS. 3 and 4, the same elements as those in FIG. 7 showing the related art are denoted by the same reference numerals, and description thereof will be omitted. 1 and 2 are diagrams for explaining an example of an AC signal used in the position control system of the present invention. FIG. 3 is a block diagram showing an example of a series of controls by the control device according to the present invention in the case of FIGS. 1 and 2 are diagrams showing a torque command value Tcom and an AC signal Tadd with respect to time on the horizontal axis. In the present invention, when the absolute value of the torque command value Tcom is small, an AC signal having a predetermined amplitude is generated, and when the absolute value of the torque command value Tcom is large, the magnitude of the AC signal is reduced. Is performed. Here, Tadd is a signal generated for the purpose of absorbing lost motion and added to the torque command value Tcom. As a result, the torque command value Tcom becomes T
The torque of the motor is generated according to the signal “add”, and the shaft of the motor vibrates by the amount of the lost motion, so that the influence of the lost motion can be removed.

For example, if the threshold value for determining whether the absolute value of the torque is large or small is a straight line indicated by Tlim in FIG. 1, the torque command value Tcom in FIG.
Is always lower than Tlim, an AC signal Tadd having a constant period and a constant amplitude, which is previously stored as data, is generated. In the case of FIGS. 1 and 2, the AC signal T
Although add is shown as a square wave, this is merely an example, and there is no particular limitation as long as it has a constant period and a constant amplitude. On the other hand, as shown in FIG.
If there is a part where m is larger than the threshold value Tlim,
As shown in FIG. 2, the torque command value Tc
The amplitude of Tadd is reduced in proportion to the value of om. If the threshold value Tlim is not exceeded, an AC signal Tadd having a constant period and a constant amplitude is generated as in FIG. As described above, the AC signal Tadd as shown in FIG.
It has become. Tad is proportional to the torque command value Tcom.
Although it has been described that the amplitude of d is reduced, this need not be particularly proportional, and various modifications are possible. As described above, AC signal Tadd generated by AC signal generating means 7 shown in FIG. 3 based on torque command value Tcom.
Is added to the torque command value Tcom by the signal adding means 5. As a result, finally, the post-addition torque command value T
com1 is generated and sent to the three-phase dividing means 6. Note that Tadd is not limited to Tcom but may be added to the position command value Xcom and the speed command value Vcom according to the control method. In addition, other processes are the same as those in the related art, and thus description thereof is omitted.

Next, another embodiment of the present invention will be described. As described above, since the lost motion exists in the mechanical system, a hysteresis curve as shown in FIG. 9 can be drawn. In this case, it can be said that in FIG. 9, the operation amount of the motor shaft corresponds to the position command value Xcom, and the operation amount of the load corresponds to the position detection value Xmes. However, the position detecting means for detecting the position detection value Xmes must be mounted on the load side, not on the motor side. In order to obtain the amount of lost motion of the mechanical system by drawing the hysteresis curve, for example, a reciprocating motion of a certain distance is performed as a test operation before a normal operation. At this time, by measuring the position command value Xcom and the position detection value Xmes, the hysteresis curve can be drawn, and the lost motion amount LM can be obtained from the curve by the above-described method. Note that a specific method of obtaining the lost motion amount LM can be realized in many ways and is not particularly limited in the present invention. In addition, obtaining the lost motion amount LM is not limited to the test operation before the normal operation, and various modifications such as online measurement during the normal operation can be considered. As described above, in the measuring means 8 as shown in FIG. 4, the position command value Xcom and the position detection value X
From mes, the amount of lost motion LM, which is the amount of hysteresis indicating the behavior of the machine axis with respect to the behavior of the motor axis, is measured, and the obtained lost motion amount LM is sent to the AC signal setting means 9. The AC signal setting means 9 obtains the necessary amplitude and cycle of the AC signal Tadd added to the torque command value Tcom based on the lost motion amount LM. The obtained AC signal Tadd is converted into a torque command value Tcom by the signal adding means 5 as shown in FIG.
, And finally generates an added torque command value Tcom1 and sends it to the three-phase dividing means 6. The other processing is the same as that of the conventional technique, and the description is omitted.

Hereinafter, an example of a method of obtaining the amplitude and cycle of the AC signal Tadd in the AC signal setting means 9 will be described. FIG. 5 is a diagram for explaining the relationship between the position, the speed, and the acceleration, and FIG. 6 is a flowchart illustrating an example of a method for obtaining the amplitude and cycle of Tadd. Before describing the process of determining the amplitude and cycle of the AC signal Tadd, the relationship among the position, velocity, and acceleration will be described first with reference to FIG. FIG. 5 is an example of a diagram showing a relationship between the acceleration α, the speed v, and the position p as the AC signal Tadd. Now, assuming that T is the torque, α is the acceleration, and J is the inertia, T = J × α− (1). Here, as shown in FIG. 5, the AC signal Tadd
It is assumed that the waveform of the acceleration α is a square wave having a constant period and a constant amplitude. In general, the velocity v due to the acceleration α is a value obtained by integrating the acceleration α with respect to time. Here, since the velocity v is the area of the square wave up to the corresponding time, it becomes a triangular wave as shown in FIG. Let α1 be the amplitude and t1 be the cycle, the amplitude v1 is v1 = α1 × (t1 / 4) − (2), and the cycle is t1 like the acceleration α. Further, since the position p based on the speed v is a value obtained by integrating the speed v with respect to time, a waveform of a quadratic curve as shown in FIG. 5 is obtained, and the amplitude p1 is p1 = v1 × (t1 / 4) ) / 2− (3), and p1 = α1 × t12 / 32− (4).

In the present invention, the lost motion amount L
The motor is operated as if lost motion is zero by vibrating the motor shaft by M. Now, when the lost motion amount LM has already been obtained from the method based on the hysteresis curve, assuming that LM / 2 = p1, which is half of the lost motion amount in the equation (4), the motor generates vibrations corresponding to the lost motion amount. It is possible to obtain the amplitude α1 and period t1 of the acceleration required to perform the operation. However, this is p1
= LM / 2 into equation (4), and LM / 2 = α1 × t12 / 32− (5), and only the relationship between α1 and t1 can be determined, and the values of α1 and t1 are obtained. It was not decided. Therefore, first, either α1 or t1 must be determined to a certain value. For that purpose, for example, the processing shown in FIG. 6 is performed to determine the value.

As shown in FIG. 6, first, before starting the normal operation of the motor, it is confirmed that the motor has stopped (S1). When the stop of the motor is confirmed, the AC signal T
A series of processes for determining the amplitude and cycle of add are performed. First,
The data of the initial AC signal amplitude Tp0, the initial AC signal cycle t0, the AC signal cycle increment td, and the inertia J are read from the memory (S2). Here, the method of reading data from the memory is well-known, and thus the description is omitted. The initial AC signal amplitude Tp0, the initial AC signal cycle t0, and the AC signal cycle increase td are constant values set in advance. After reading the data, the initial AC signal amplitude Tp0 is substituted for the execution AC signal amplitude Tp, and the initial oscillation period t0 is substituted for the execution AC signal period t (S
3), a test operation is performed (S4). Here, the test operation means that the torque command value Tcom = 0 and the AC signal Tad
Only d is instructed. When the test operation is started, the electric motor vibrates at a constant cycle and amplitude by the AC signal Tadd. At this time, the position detection value Xmes is detected, and the amplitude Xwd of the vibration of the electric motor can be obtained from the maximum value and the minimum value of the position detection value Xmes. At this time, the amplitude Xwd and LM are compared (S5), and if Xwd ≦ LM, the AC signal cycle increase td is added to the AC signal cycle t at the time of execution.
Is added and recalculated (S6, S7). Recalculation is t
Assuming that 1 = t, it is substituted into equation (5) to obtain α1, and α = α1
Tp is obtained by substituting into Equation (1). When new t and Tp are obtained by the recalculation, the test operation is performed again, and a series of processes of detecting the amplitude Xwd and comparing with the LM are repeated until Xwd> LM (S5). Xwd
If> LM, t = t−td is set, and the cycle is returned to the immediately preceding execution-time AC signal cycle (S8, S9). Since Tp obtained here is the amplitude of the AC signal Tadd, and t1 is the cycle of the AC signal Tadd, it means that the amplitude and the cycle of the AC signal Tadd have been determined.

Here, the reason for performing the above processing will be described below. It is generally known that, since an inductance is present in the winding of a motor, even if a current command equivalent to, for example, the waveform indicated by α in FIG. 5 is given, a current does not actually flow as instructed and a delay occurs. . The shorter the cycle of the current command is, the more noticeable the delay is. The current command and the torque command Tcom usually have the same waveform. Therefore, in the test operation, the shorter the cycle t1 of the AC signal is, the shorter the cycle of the AC signal is. Therefore, it can be said that the torque actually generated in the electric motor does not sufficiently respond to the torque command value Tcom and the delay increases. The fact that the torque actually generated in the electric motor does not sufficiently respond to the torque command value Tcom means that the response also delays with respect to the velocity waveform indicated by v and the position waveform indicated by p in FIG. Therefore, even if α1 and t1 are calculated based on the equation (5), the shorter t1 is, the more the LM of which the amplitude Xwd of the vibration of the electric motor is the desired magnitude does not operate. Become. In this case, since the object of vibrating the motor shaft by the lost motion amount LM cannot be achieved, the AC signal cycle t at the time of execution is gradually reduced as described above, and the amplitude Xwd of the vibration of the motor is actually reduced to LM. Try to be bigger. In this case, in FIG. 6, Tp is recalculated based on the equations (1) and (5), and the amplitude of the AC signal Tadd is obtained each time. (5)
There may be various other methods, such as calculating another formula without using the formula, and not performing recalculation. The present invention is not particularly limited. In FIG. 6, the AC signal cycle t at the time of execution immediately before Xwd> LM is set to the cycle t1 of the AC signal. However, it is not possible to vibrate more than the lost motion amount LM. This is because it is assumed that the condition is such that Xwd as large as possible can be obtained within a range not exceeding the lost motion amount LM because it may cause a cause. However, this is not particularly limited in the present invention. For the reasons described above, for example, a series of processes as shown in FIG. 6 is performed to determine the amplitude and cycle of the AC signal Tadd. It should be noted that whether or not the processing as shown in FIG. 6 is performed is not particularly limited in the present invention, and various modifications such as not performing the processing or performing other processing are conceivable. The above is an explanation of an example of the processing in the AC signal setting means 9.

Further, in some cases, the above-described processing is added or changed so that the frequency which is the reciprocal of the cycle of the set AC signal Tadd does not become close to the frequency assuming that the resonance frequency of the mechanical system is known in advance. It is possible. Since various processes can be considered at this time,
In the present invention, although not particularly limited and the description is omitted, it is sufficient that a desired action is obtained.

Although shown in each of the descriptions, various modifications can be considered for the following items, and are not limited to those described in the description. Therefore, the present invention is not particularly limited. First, the configuration of a block diagram showing a series of controls of the control device as shown in FIG. 3 is not limited to the format shown in the diagram, and various modifications can be considered. Also,
As described above, when determining the amplitude and the period of the AC signal Tadd, the processing mode and calculation method are not limited to those described in the embodiment, and are not particularly limited in the embodiment. In particular, the shape of the AC signal is not limited to a square wave, and various modified examples such as a sine wave and a triangular wave are conceivable. In addition, each processing is not limited to offline processing but is performed online to compensate in real time. Many variations are possible. In the description of the present embodiment, the AC signal Ta
Although the description has been given of the method of adding dd to the control loop with the torque command value Tcom, this may be added to the speed loop, the position loop, or the like, and is not particularly limited.

[0016]

According to the present invention, a constant or variable AC signal is added according to the amount of lost motion of the mechanical system, and in some cases, the frequency of the signal to be set is set so as not to be near the resonance frequency of the mechanical system. Therefore, it is possible to control the electric motor so as to absorb the lost motion of the mechanical system, and there is an effect that the oscillation of the electric motor and the resonance of the mechanical system do not occur.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of waveforms of a torque command value Tcom and an AC signal Tadd with respect to time in the present invention.

FIG. 2 is a diagram showing an example of waveforms of a torque command value Tcom and an AC signal Tadd with respect to time in the present invention.

FIG. 3 is an example of a block diagram illustrating processing of a motor control device according to the present invention.

FIG. 4 is another example of a block diagram showing processing of the control device for the electric motor according to the present invention.

FIG. 5 is a diagram generally showing a relationship among acceleration, velocity, and position.

FIG. 6 is a flowchart illustrating an example of processing in an AC signal setting unit according to the present invention.

FIG. 7 is an example of a block diagram showing processing of a conventional synchronous motor control device.

FIG. 8 is an example of an enlarged view of the vicinity of meshing between a first gear portion and a second gear portion in gear driving.

FIG. 9 is an example of a diagram showing a hysteresis curve of a mechanical system for explaining a lost motion amount.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 first comparator, 2 position loop gain, 3 second comparator, 4 speed loop gain, 5 signal adding means, 6 three-phase dividing means, 7 AC signal generating means, 8 measuring means, 9
AC signal setting means, 10 first gear section, 11 second gear section.

Claims (3)

[Claims] 1. A position control system for controlling the position of a machine having a flexible structure, such as backlash or mechanical deflection, which is a play in a mechanical system, with an electric motor. AC signal generating means for generating an AC signal having an amplitude of the following magnitude and reducing the magnitude of the AC signal when the absolute value of the torque command value is large; and an electric motor such as a position signal, a speed signal, and a torque signal. Signal adding means for adding the AC signal to any of the signals for controlling the position control. 2. The position control system according to claim 1, wherein, in place of said AC signal generating means, a position detecting means for detecting a position of a load; A position control system comprising: a measuring unit for measuring a hysteresis amount indicating a behavior of a machine axis with respect to a behavior; and an AC signal setting unit for setting an amplitude or a frequency of the AC signal from an output of the measuring unit. 3. The position control system according to claim 2, wherein the setting of the AC signal set by the AC signal setting means based on an output of the measuring means does not become a resonance frequency of a mechanical system. Characterized position control system.