JPS6253195A - Digital positioning controller for stepping motor - Google Patents

Abstract

PURPOSE:To change the position of a stepping motor minutely regardless of mechanical feed-pitches by annexing a micro-feed circuit. CONSTITUTION:When a linear stepping motor 5 is operated, a target position is given from the outside while a positional error between the target position and the current position of the linear stepping motor is obtained at every feedback and sampling time through a position detector 6 and an A/D converter 7', and the motor 5 is controlled so that the positional error is eliminated. A micro-feed circuit 4 has a ROM in which the combination of a current value corresponding to the address of the position of equilibrium is memorized, and a current value at A phase and a current value at B phase are combined properly, thus arbitrarily setting the position of the position of equilibrium of the linear stepping motor regardless of mechanical feed-pitches.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a digital positioning control device for a step motor that can perform minute positioning regardless of mechanical feed pitch.

[Prior art and its problems]

A step motor is a motor that rotates (or moves) by a fixed angle (or distance) each time an input pulse is applied, and has been widely used as a drive unit of conventional positioning devices because it can simplify the servo mechanism. For example, in an NC machine tool, a table drive actuator is used to position the X-Y table, in a magnetic disk device such as a floppy disk device, a magnetic head drive actuator is used to position the magnetic head on a data track, and in a printer device, a carriage drive is used to position the print head. Each is used as an actuator.

For example, in the case of bipolar driving a two-phase linear step motor, the step motor driving method described above is based on the equilibrium point position determined by combining the directions of excitation currents flowing in the A phase and B phase, respectively. is moved by sequentially switching the excitation current, and is driven by the thrust generated by the deviation between the equilibrium point position and the current position.

In recent years, as step motors have been applied to a wider range of fields, there is an increasing need to operate step motors with minute precision.For example, floppy disk devices and fixed magnetic disk devices, which are becoming larger in size, are This is a notable example. By the way, in order to operate the step motor so as to perform fine positioning in the conventional drive method, it is necessary to provide a mechanical structure with a feed pitch corresponding to the required feed accuracy. However, there is generally a limit to how much accuracy can be mechanically increased, and as a result, the positioning accuracy cannot be increased that much, resulting in the problem of not being able to meet social demands.

In addition, the motion in a step motor is generally described below (
1) It is expressed by the spring-mass system of equation.

Therefore, without the influence of frictional force etc., the step motor has the characteristic that it will not converge to the equilibrium point position and will continue to vibrate, and when performing open loop control such as the above drive method, it is necessary to use the spring-mass system. There is a problem that settling time becomes long due to residual vibration. Furthermore, there is also the problem that high-precision, high-speed positioning is not possible due to the effects of static friction and the like.

Mε 10 k ε = O (1) Here, M is the mass of the moving part of the linear step motor, ε is the positional deviation between the equilibrium point position and the current position in the linear step motor, k
is a spring constant, and ε represents the second derivative of ε with respect to time.

[Purpose of the invention]

It is an object of the present invention to provide a digital step motor that compensates for the operating characteristics of the conventional step motor and that allows the position of the step motor to be minutely changed without being constrained by the feed pitch determined by the mechanical structure of the step motor. An object of the present invention is to provide a positioning control device.

[Structure of the invention]

The present invention includes a step motor, a first A/D converter that converts a target position signal indicating a target position to be followed by the step motor into a digital signal at fixed sampling time intervals, and outputs the digital signal during the sampling time. , a position detection means for detecting the position of the step motor; a second A/D converter that converts the output signal of the position detection means into a digital signal at each sampling time and outputs it during the sampling time; a subtracter that calculates an error between the output signal of the first A/D converter and the output signal of the second A/D converter; and an integration unit that integrates the output signal of the subtracter at each sampling time. means and said first
a digital compensation filter to which the output signal of the A/D converter, the output signal of the second A/D converter, and the output signal of the integration means are input; A step motor micro-feed circuit includes a memory element that outputs an excitation current value to each phase of the motor, and an amplifier that applies a current to the step motor via a low-pass filter according to the output value of the memory element. The present invention is characterized in that the dynamic characteristics are compensated by feedback control using the digital integrator and the digital compensation filter having three inputs and one output.

〔Example〕 The present invention will be described in detail below using the drawings.

FIG. 1 is a block diagram showing the configuration of a step motor digital positioning control device according to the present invention. In this embodiment, the object to be controlled is a two-phase linear step motor. In the following description, signals and the values represented by the signals are described using the same symbol.

Let T be the sampling time. A target position signal a indicating a target position to be followed by a two-phase linear step motor (hereinafter referred to as a linear step motor) 5 is given from the outside. This target position signal a is converted into a digital signal by an A/D converter 7 at every sampling time T, and is supplied to a sampling time T amount subtracter 1 and a digital compensation filter 3. On the other hand, the current position X of the linear step motor is detected as a position signal C by the position detector 6. This position signal C is converted into a digital signal d by the A/D converter 7' at every sampling time T, and is supplied to the amount subtracter 1 of the sampling time T and the digital compensation filter 3. The subtracter 1 receives the output signal from the A/D converter 7.7'.

d is input to calculate the position error between the target position to be followed by the linear step motor 5 and the current position of the linear step motor 5, and the resulting position error signal e is output to the integrator 2. The integrator 2 integrates the position error signal e at every sampling time T, and outputs its production value f to the digital compensation filter 3 during the sampling time T.

The digital compensation filter 3 calculates the equilibrium point address value U of the linear step motor based on the input output signals S, d and the output value f.

This equilibrium point address value U is △ of the sampling time T.
After the sampling time T, that is, at time T+Δ, the signal is outputted to the minute feed circuit 4 of the linear step motor. The minute feed circuit 4 generates a current g corresponding to each of the A phase and B phase of the linear step motor 5 based on the equilibrium point address value U.

g', thereby changing the equilibrium point of the linear step motor 5 and activating the linear step motor 5.

In the above, when operating the linear step motor 5, a target position is given from the outside, and the current position of the linear step motor is detected by the position detector 6 and the A/D converter 7.
', the position error between the target position and the current position is obtained at every sampling time T, and control is performed to eliminate this position error. Above integrator 2
is a digital integrator, and the position of the linear step motor 5 is controlled by this integral compensation so that it constantly matches the target position to be tracked. Further, as will be described later, the stability of the feedback control system is satisfied by the digital compensation filter 3.

Regarding the above sampling time T and output time Δ,
Time management is performed by a timer (not shown). Further, as the position detector 6, any conventional detector such as an optical encoder can be used.

Next, the configuration of the minute feed circuit 4 will be described in detail. FIG. 2 is a block diagram showing an example of the configuration of a minute feed circuit. The minute feed circuit 4 receives the equilibrium point address value U of the linear step motor 5 given from the digital compensation filter 3, and outputs the current to be given to each of the A phase and B phase of the linear step motor. ROM8.8
D/A converters 9, 9' convert the output value h' from a digital signal to an analog signal;
9' output value', Nyquist frequency at J' (1/
Low-pass filter 1 that blocks frequency components above 2T)
0.10', and an amplifier 11.11' that amplifies the output values q and q' of the low-pass filter 10.10' and obtains currents g and g' to be passed through the A and B phases of the linear step motor. .

By the way, the position of the equilibrium point of the linear step motor can be arbitrarily set by appropriately combining the A-phase current value and the B-phase current value, regardless of the mechanical feed pitch. In other words, when a certain amount of current is passed through each of the A-phase and B-phase, there is always an equilibrium point determined by the combination of the current values, and the position of this equilibrium point depends only on the excitation current of the A-phase and B-phase. However, it is independent of mechanical feed pitch. Therefore, when the equilibrium point position due to a certain combination of currents is set to the reference address (address value 0),
The positional deviation from that point can be used as the equilibrium point address of the linear step motor, and the combination of current values corresponding to this equilibrium point address is stored in the ROMs 8 and 8'. However, the combination of the A-phase current value and the B-phase current value is set so that the maximum static thrust is constant.

FIG. 3 shows this situation, with the reference address (address value 0) determined by a certain combination of currents, the equilibrium point address u of the linear step motor expressed by the position deviation from that point, The static thrust characteristics at u′ and u” are shown. In FIG. 3, there are countless equilibrium points on the horizontal axis, but in reality, the number of equilibrium points is determined by the output value U of the digital compensation filter 3. It is determined by the resolution.The position of the step motor is also given as the position deviation from the reference address.

FIG. 4 shows an example of a specific configuration of the low-pass filter 10.10'. This low pass filter is an operational amplifier 12
A circuit consisting of resistors R, , R2 and capacitor C2 is connected to a non-inverting input terminal, and its output is fed back to an intermediate node between resistors R, , R2 via the inverting input terminal and capacitor CI. ing. The transfer function of this low-pass filter is expressed by a second-order transfer function Gzp(s) as shown in equation (2) below.

Here, S is a Laplace transform operator.

G, p (s) = w2/ (S2+ 2 ・ζws
+w2) W in the above formula (2), and constant R of the circuit in Figure 4
The following relationship exists between 1°R2,C,,C2,.

w = t/J Ken 7-cho [-17 (3) ζ = C2・(R, +R2) /2 T1 at C■] [As explained above, the minute feed circuit 4 balances the linear step motor 5. The position of the point can be arbitrarily set regardless of the feed pitch determined by the mechanical structure.

In addition, when the minute feed circuit 4 is connected to the linear step motor 5, as is clear from FIG. 3, the input/output between the equilibrium point address value U of the linear step motor 5 and the position The relationship is expressed by equation (5).

Mx + kx = ux (5)
Here, M and k are the mass and spring constant of the linear step motor 5, and X represents the second-order differential of X with respect to time.

A system that inputs the address value U of the equilibrium point of the linear step motor 5 and outputs the position X of the linear step motor 5 is constructed using a timer as shown in FIG. Add and configure, t=NT (N=0゜1.2.・・・・・・・・・)
Focusing on the sampling time of , and deriving the state equation with discrete time values, the equation (6) is obtained. Dead time 1
3 is a dead time for taking into account calculation time delays caused by the integrator 2 and the digital compensation filter 3, and ■ is an input to the dead time 13. Also, X is 1 with respect to the time of X
Represents the order differential.

Here, X (NT) is a state vector copy Y (NT) is an output vector, which is given by the following equation.

Furthermore, each coefficient matrix in equation (6) has the following structure.

and exp (.) is a matrix exponential function.

The system expressed by equation (6) is controllable and observable, and the observability index is 2.

Incidentally, the function of the integrator 2 can be represented by an adder 14 and a shift register 15, as shown in the block diagram shown in FIG. In FIG. 6, 2 is the Z-transform operator.

In a system in which the system in FIG. 5 and the integrator 2 in FIG. 6 are connected in series as shown in FIG. 7, the system in FIG. Because there is no
It can be controlled from the input V with a dead time of 12. Therefore, when input V with dead time 13 is input, linear step motor 5
The system shown in FIG. 7 can be stabilized by a first-order digital compensation filter by outputting a position signal d representing the position of , and an output signal f of the integrator 2.

Further, for example, if a configuration example of a digital compensation filter is described using Z-transform operator 2, it can be represented in a block diagram as shown in FIG.

In FIG. 8, 16 is a shift register, 17.18 is an adder, 19.20.21.22.23.24.25 are αl, α2. α3. α2. α3. α6. This is a multiplier that multiplies α by a constant. α1 to α7 are real constants. Further, 13 is a dead time of 6 hours taking into account the time delay due to the calculation time mentioned above, and is a dead time in which V is always output as U at 6 hours after sampling time t=NT, that is, at time t=NT+Δ. It is.

At this time, the pulse transfer function Gbv(z) from the output signal of the A/D converter 7 of the target position signal a to the output V of the digital compensation filter in FIG. The pulse transfer function Gdv (Z) from the output signal d of the A/D converter 7' at the current position X of the J near step motor 5 to the output of the digital compensation filter, and from the output f of the integrator 2 Pulse transfer function G r to output V
v (z) are as follows.

cbv(Z)=(ff+j z+a2- z)/(z
-a,・z−αt) (7) Gdv(z)=, (α,・
z+a<・z)/(z−ae・z−αt) (8) Gr
v(z)=(αs j z)/(z-a6・z-α,)
(9) The pulse transfer function is expressed as quadratic because the dead time 13 is treated as a time delay z −1.

Furthermore, in the feedback control system shown in Fig. 1,
The pulse transfer function W(z) from the target position signal to the position X of the linear step motor 5 is as follows.

W(z)=N,(z)・N2(z)/D(z)
(10) However, N I (z) is a quadratic real coefficient polynomial that can be arbitrarily specified by the real constants α1゜α2 shown in Figure 8, and N2 (Z) is the system expressed by equation (6). It is a polynomial that indicates the zero points. D(Z) is a real constant α3
．． α4. α5. α6. This is a polynomial that can be arbitrarily determined by α7. That is, by specifying the root of D(z)-〇 within the unit circle of the Z plane, the feedback control system shown in FIG. 1 can be obtained.

The response speed is limited by the sampling frequency, but the real constant α3. α4. α5゜α6. It can be set using α7. In addition, since the pulse transfer function W (zH,: zero point (represented by N+(z)) from the target position signal to the position X of the linear step motor 5 can be added using the real constants α1 and α2, only stability However, the digital compensation filter 3 makes it possible to improve the response.

For example, consider a linear step motor where M=2og and M=3.21ON/m. Sampling time T is 1
It is assumed that the calculation time Δ is 0.5 milliseconds. At this time, the coefficient matrix of equation (6) is as follows.

Furthermore, the constant α, of the digital compensation filter.

α2. α3. α4. α6. α6. If α7 is selected as follows, the pulse transfer function Gbv(z) from the output signal of the A/D converter 7 of the target position signal a to the output V of the digital compensation filter in FIG.
The pulse transfer function Gd from the output signal d of the A/D converter 7' at the current position X to the output V of the digital compensation filter
v(z) and the pulse transfer function cry(z) from the output f of the integrator 2 to the output V of the digital compensation filter, respectively, are as follows.

α, =0.6548486 α2=0.45
05947α3 = 0.2624751 α,
=0.5490575α, =0.4664479
α, = −1,186026α, = −0,
1963472 N+ (z
), N2 (z) and D(z) are as follows.

N, (z) =0.1266619 ・(z−0
,14661) ・(z-0,16530) (1
4) N, (Z) = (z+0.1989098)
・(z+5.027404)D (z) = z5
-0.3654802 z'+6.645129X10
-3z'+0.01256689 z"-1,8190
56z+ 7.675294 x 1O-5 (16) Also, the roots of D(z)=0 are 0.12245 and 0.130
03.

0.14661.0.16530. -0.19891
It can be seen that the digital compensation filter 3 can stabilize the signal.

In the above embodiment, the integrator 2 and the digital compensation filter 3 are a shift register, an adder, and a multiplier.

The case where this is implemented in hardware using a timer has been explained. However, as shown in FIGS. 6 and 8, since the integrator 2 and the digital compensation filter 3 are represented by the Z-transform operator 2, it is not possible to solve the difference equation using a digital computer as a software program. It is also possible to realize this.

Furthermore, the present invention is not limited to two-phase linear step motors;
Of course, it can be applied to other step motors.

〔Effect of the invention〕

As is clear from the above explanation, according to the present invention, since a fine feed circuit is attached to the control circuit of the step motor, the step motor can be finely fed, which is related to the mechanical feed pitch. Furthermore, since the step motor is feedback-controlled using an integrator and a digital compensation filter, the step motor can be positioned at high speed and with high accuracy.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of a digital positioning control device for a step motor according to the present invention, Fig. 2 is a block diagram showing an example of the configuration of a minute feed circuit, and Fig. 3 is an address of each equilibrium point of a linear step motor. Fig. 4 is a circuit diagram showing the specific configuration of the low-pass filter, Fig. 5 is a block diagram of the control device with addition of dead time evening and f-mass, Figure 6 is a block diagram showing the function of the integrator, Figure 7 is an open loop block diagram with the digital compensation filter removed from Figure 1, and Figure 8 is the Z-transform operator 2.
FIG. 2 is a block diagram showing an example of the configuration of a digital compensation filter using the following. 1 ・・・・・・・・・・・・ Subtractor 2 ・・・・・・
・・・・・・・・・ Totalizer 3 ・・・・・・・・・・・・
Digital compensation filter 4 ・・・・・・・・・・・・
・Minute feed circuit 5 ・・・・・・・・・・・・ 2-phase linear step motor 6 ・・・・・・・・・・・・
Position detector 7.7'... A/D converter 8.8'... ROM 10.10'... Low-pass filter agent
Patent Attorney Yoshiyuki Iwasa Figure 4 14 Power Lifting Device Figure 6

Claims (1)

[Claims] (1) a step motor; and a first A/D converter that converts a target position signal indicating a target position to be followed by the step motor into a digital signal at a certain sampling time, and outputs the digital signal during the sampling time; a position detecting means for detecting the position of the step motor; a second A/D converter for converting the output signal of the position detecting means into a digital signal at each sampling time and outputting it during the sampling time; a subtracter for calculating an error between the output signal of the first A/D converter and the output signal of the second A/D converter; and an integrating means for integrating the output signal of the subtracter at each sampling time. , the first A
a digital compensation filter to which the output signal of the A/D converter, the output signal of the second A/D converter, and the output signal of the integration means are input; It consists of a step motor micro-feed circuit including a memory element that outputs the excitation current value to each phase and an amplifier that applies a current to the step motor via a low-pass filter according to the output value of the memory element, and dynamic characteristics of the step motor. A digital positioning control device for a step motor, characterized in that compensation is performed by feedback control using the digital integrator and the digital compensation filter having three inputs and one output.