JP3351979B2 - Position control system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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, or the like can be obtained is known. These control the position, speed, current, etc., 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 illustrating 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. Thereafter, the three-phase dividing means 6 uses 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 motor, there are various possible ways of connecting the shaft and the load. For example, a belt, a pulley, a gear, a ball screw, and the like are conceivable. Among them, when performing gear driving, the following may be considered. As is well known, gear drives are widely used because of their 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, during gear driving, between the first gear portion 10 and the second gear portion 11 that are engaged with each other, 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 portion 11 is on the side to be driven by the electric motor. Between the first gear unit 10 and the second gear unit 11, there is a mechanical play indicated by BR in the drawing. This is commonly referred to as backlash. It is known that this backlash is always necessary when gear driving is performed, but if the backlash becomes larger than necessary, there is a problem caused by 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 that the motor receives from the load becomes particularly large, so that the control of the motor becomes unstable. That is, during normal operation, the direction in which the torque of the motor is generated is reversed during rotation, but in this case, the teeth of the gear collide with each other. Since the collision of the teeth with the teeth 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 so-called dead zones of a mechanical system in which no load is applied despite the rotation of the electric motor. The cause of the dead zone is not only the backlash, which is a play in the mechanical system, but also various things such as a particularly large deflection when the ball screw is driven and a particularly large extension of the belt or pulley when the belt or pulley is driven. The description of each of them is publicly known and thus will be omitted. All of the backlash, deflection, and the like that cause the dead zone are 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 with a gentle curve is due to the fact that factors such as deflection and elongation are gradually eliminated. The above is the description of the hysteresis curve of FIG. 9. 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, has a large adverse effect on 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 is likely to occur in a mechanical system in which lost motion such as backlash and deflection is large. The present invention has been made in view of the above problems, and has as its object to provide a position control system capable of absorbing lost motion and performing accurate position control.

[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 unit for measuring a hysteresis amount indicating a behavior of the machine shaft with respect to a behavior of the motor shaft; and an AC signal setting unit for setting an amplitude or a cycle of the AC signal based on an output of the measuring unit. 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 cases 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 magnitude 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
Since the torque of the motor is generated according to the signal of “add” and the shaft of the motor vibrates by the amount of the lost motion, the influence of the lost motion can be removed.

For example, assuming that a threshold for determining whether the absolute value of the torque is large or small is a straight line indicated by Tlim in FIG. 1, in FIG. 1, the torque command value Tcom is always lower than Tlim. An AC signal Tadd having a constant period and a constant amplitude is generated. In the case of FIGS. 1 and 2, the AC signal Ta
Although dd 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 portion where is larger than the threshold Tlim, FIG.
As shown in FIG.
Decrease the amplitude of Tadd in proportion to the value of. Also, the threshold
If the value does not exceed Tlim, a fixed period is set as in FIG.
An AC signal Tadd having a constant amplitude is generated. As described above, the AC signal Tadd as shown in FIG. 2 is obtained. Although it has been described that the amplitude of Tadd is reduced in proportion to the torque command value Tcom, this need not be particularly proportional, and various modifications can be considered. The AC signal Tadd generated by the AC signal generating means 7 shown in FIG. 3 based on the torque command value Tcom as described above is added to the torque command value Tcom by the signal adding means 5.
As a result, the post-addition torque command value Tcom1 is finally generated and sent to the three-phase dividing means 6. In addition,
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 of the conventional technology, 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 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 in FIG. 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. It should be noted that a specific method for 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, 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 shaft with respect to the behavior of the motor shaft, 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 applied to the 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 prior art, and the description is omitted.

Hereinafter, an example of a method of obtaining the amplitude and the 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 showing 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 velocity 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 speed 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 an area of a square wave until the corresponding time, the velocity v 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 thus 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 shaft of the motor for M times. 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 for performing the operation. However, this means that 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 this 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, a method of reading data from the memory is well-known, and thus description thereof is omitted. The initial AC signal amplitude Tp0, the initial AC signal period t0, and the AC signal period increase amount td are constant values set in advance. After reading the data, the initial AC signal amplitude Tp0 is substituted for the runtime AC signal amplitude Tp, and the initial vibration period t0 is substituted for the runtime 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 amount td is added to the execution AC signal cycle t.
Is added and recalculated (S6, S7). Recalculation is t
Substituting 1 = t into equation (5) to obtain α1, α = α1
And 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 previous execution 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 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 a 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. Thus, 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 respond sufficiently to the torque command value Tcom means that the response is also delayed 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), as t1 becomes shorter, as a result, the motor does not operate only for the LM having the desired amplitude Xwd of vibration. Become. In this case, since the purpose 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 shortened as described above, and the amplitude Xwd of the vibration of the motor actually becomes 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)
Various formulas may be obtained without using, and various methods such as recalculation may not be performed. The present invention is not particularly limited. In FIG. 6, the AC signal period t at the time of execution immediately before Xwd> LM is set to the period t1 of the AC signal. This is because it is assumed that the condition for obtaining Xwd as large as possible within a range not exceeding the lost motion amount LM is considered to be a cause. However, this is not particularly limited in the present invention. For the reasons described above, for example, a series of processing 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 the process at this time can be various,
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 the 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 cycle of the AC signal Tadd, the processing form 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 depending on 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 a waveform of a torque command value Tcom and an AC signal Tadd with respect to time in the present invention.

FIG. 2 is a diagram illustrating an example of a waveform 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 showing a process of a motor control device according to the present invention.

FIG. 4 is another example of a block diagram illustrating a process of a motor control device 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.

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G05D 3/00-3/20 H02P 5/00

Claims (3)

(57) [Claims] In a position control system for controlling gear backlash by an electric motor, an AC signal having a predetermined magnitude is generated during rotation if an absolute value of a torque command value is smaller than a predetermined threshold value. An AC signal generating means for reducing the magnitude of the AC signal when the absolute value of the torque command value is larger than a predetermined threshold during rotation; and an electric motor for a position signal, a speed signal, a torque signal, and the like. Signal adding means for adding the AC signal to any of the signals for controlling the position control system. 2. The position control system according to claim 1, wherein said AC signal generating means is replaced with a position detecting means for detecting a position of a load, and a change in a position detecting signal from said position detecting means is used to control the motor shaft. A position control system comprising: a measuring unit that measures a hysteresis amount indicating a behavior of a machine axis with respect to a behavior; and an AC signal setting unit that sets 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 the output of the measuring means does not become a resonance frequency of a mechanical system. Characterized position control system.