JPH0514923B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a control method for rapidly moving and stopping an actuator that is stopped at a certain position to a position that is an arbitrary distance away.

[Prior art]

Actuators are used in many mechanical devices such as machine tools, robots, integrated circuit exposure equipment, magnetic disks, and optical disks, and are required to move and stop from any stop position to any other position at high speed. . For example, in magnetic disks and optical disks used as file memories in computers, the magnetic head or optical head is driven by an actuator and randomly moved and positioned on multiple tracks, but the question is how to shorten this positioning time. This is a major issue that will determine the processing power of electronic computers.

In a conventional magnetic disk device, Fig. 1a
The movement and positioning of the actuator was controlled using a speed control loop as shown in the figure below.

That is, a speed reference curve (solid line) as shown in FIG. The head is moved to the target track by feeding back the speed of the actuator 4 (broken line) and controlling the speed to follow the speed standard via the speed error detection circuit 2 and power amplifier 3.

When the above-described closed-loop control is performed, the relationship between the speed v and the speed reference v _ref is as shown in equation (1).

v=1/1+S/Gv _ref (1) In equation (1), the Labrus transformer is used, and G is the gain of the loop.

As can be seen from equation (1), in this conventional method, the speed follows the speed standard well at low frequencies, but does not follow it at high frequencies. On the other hand, to move faster,
It is necessary to make the speed standard steeper, that is, to increase the deceleration, but in that case, the speed standard will have many high frequency components and the speed will no longer follow the speed standard.
In order to make it follow this, it is possible to increase the loop gain G, but if the loop gain G is increased, the closed loop will oscillate at the 2-3KHz mechanical resonance point that exists in the actuator, so increasing the loop gain is a realistic method. Not.

As described above, the conventional movement control method that simply controls the speed in a closed loop has the disadvantage that it is not possible to rapidly decelerate the movement, and as a result, the movement time cannot be shortened.

[Summary of the invention]

The present invention has been made in view of the above-mentioned drawbacks, and its purpose is to provide a control method that can further shorten the travel time of an actuator under conditions where the maximum drive power is limited. It's about doing.

In order to achieve such an objective, the control method of the present invention applies a constant accelerating voltage and current to the actuator to move it by open loop drive when the access distance of the actuator is larger than the first set distance. When the moving distance of the actuator exceeds the second set distance, a constant deceleration voltage and current are applied to reduce the moving speed by open-loop driving, and this deceleration causes the actuator's moving speed to reach the residual distance. When the speed drops below a predetermined reference speed, voltage and current are applied to the actuator according to the difference between the reference speed and the actuator's movement speed, and follow-up control is performed using closed-loop drive, thereby controlling the actuator's access. If the distance is smaller than the first set distance, apply a constant acceleration voltage and current to the actuator to move it by open loop drive,
When the moving speed of the actuator reaches a reference speed or higher, voltage and current are applied to the actuator according to the difference between this reference speed and the moving speed of the actuator, and follow-up control is performed using closed-loop drive. .

〔Example〕

The present invention will be described in detail below along with examples. FIG. 2 is a block diagram showing one embodiment of the present invention, and the same parts as in FIG. 1 are given the same reference numerals.

The position detection circuit 17 is a circuit that detects the position of the actuator 4 on the magnetic disk or optical disk, and its output extends to the movement distance detection circuit 18, the residual distance detection circuit 20, and the speed detection circuit 1. The position detector 17 can be constructed using a known technique. For example, in the case of a magnetic disk, the servo information written on the servo disk is read out and waveform processed by a servo head attached to an actuator, or in the case of an optical disk, it is read out from a fixed photodiode. Light is irradiated onto a scale with bright and dark slits attached to the actuator, and a fixed photodetector detects the transmitted or reflected light and processes the waveform to detect the position. An example of a position waveform output from a position detector on a magnetic disk is shown in FIG. 3a. In FIG. 3a, the position waveform has a 0 level for each track pitch A of the magnetic disk, and is a triangular waveform with positive and negative levels centered on 0 in proportion to the moving distance of the head.

As shown in FIG. 3b, the movement distance detection circuit 18 generates one pulse every time the actuator moves a certain distance (in this embodiment, the distance of the disk) based on the position detected by the position detection circuit 17. The pulse is input to the countdown input terminals of the counter 14 and the counter 16.

The counter 14 is set to an initial value by the control unit 12. This initial value is input to the control unit 12 from a higher-level device (not shown) via the transmission line 11. It is calculated based on the access command and the access distance (number of tracks), and is one half of the value obtained by subtracting the second specified distance (number of tracks) from the access distance (described later) (if it is not divisible, use the decimal point). (hereinafter rounded down). The count contents of the counter 14 are output to the control section 12.

The counter 16 is set by the control unit 12 using the access distance value as an initial value, and the content is subtracted by one count by the pulse output from the movement distance detection circuit 18, and the content is transferred to the residual distance detection circuit 2.
Output to 0.

The residual distance detection circuit 20 is a circuit that detects the residual distance of access from the output of the counter 16 and the output of the position detection circuit 17, and its output is transmitted to the reference speed generation circuit 21 and the access completion condition detection circuit 37. is input. Specifically, the binary digital value of the output of the counter 16 is input to a digital-to-analog conversion element to convert it into a staircase waveform output as shown in FIG. 3c, and this output is subjected to position detection as shown in FIG. 3a. The residual distance is detected as an analog quantity by adding together the waveform shown in FIG. 3d, in which the slope of the output of the circuit 17 is made negative and the gain is changed to match the level step of the digital-to-analog conversion element.

The reference speed generation circuit 21 is the residual distance detection circuit 2
This circuit generates a standard speed proportional to the square root of the residual distance as an electrical signal by outputting from 0, and is constructed of a diode network that utilizes the square characteristic of current and voltage of known diodes. The output of the reference speed generation circuit 21 is input to the comparison circuit 23 and the speed error detection circuit 2.

The comparison circuit 23 compares the output of the reference speed generation circuit 21 and the output of the speed detection circuit 1, and outputs a logic signal that becomes "1" when the output of the speed detection circuit 1 exceeds the output of the reference speed generation circuit 21. do. The speed detection circuit 1 may be configured to differentiate the output of the position detection circuit 17, that is, the position waveform shown in FIG. 3a, and detect its absolute value. The configuration may be such that the voltage generated across the terminal is detected.

The speed error detection circuit 2 is a circuit that calculates the difference between the output of the speed detector 1 and the output of the reference speed generation circuit 21, and then outputs a signal multiplied by a constant to the gate circuit 33. The speed error from the standard speed determined according to the distance is detected.

The gate circuit 33 inputs the output of the speed error detection circuit 2, and ORs the output of the speed error detection circuit 2 only while the loop control command signal obtained from the control unit 12 via the connection line 32 is on. Output to circuit 34.

The gate circuit 28 inputs an instruction signal of a constant acceleration voltage or acceleration current from the input line 27, and ORs the instruction signal only while the acceleration instruction signal obtained from the control section 12 via the connection line 26 is in the ON state. Output to circuit 34.

The gate circuit 31 inputs a deceleration voltage or deceleration current instruction signal whose absolute value is equal to and opposite to the above-mentioned acceleration instruction signal from the input line 30, and controls the control unit 1.
A deceleration voltage or deceleration current instruction signal is output to the OR circuit 34 only while the deceleration command signal obtained from 2 through the connection line 29 is on.

The OR circuit 34 sums the outputs of the gate circuits 28, 31, and 33 and outputs the sum to the power amplifier 3, and the power amplifier 3 applies a voltage or current proportional to the output of the OR circuit 34 to the actuator 4. to drive.

Next, the operation of this embodiment will be explained using the flowchart shown in FIG.

First, the access command and access distance are line 1.
1 to the control unit 12, the access command is detected in the start routine 100. For example, in the case of magnetic disks, optical disks, etc., the access distance is specified as a binary digital quantity, which is the difference between the track number located before receiving the access command and the track number to be accessed.

In routine 101, a value equal to half of the value obtained by subtracting the second specified distance from the access distance is set in the counter 14 in a digital quantity. The method for determining the second specified distance will be explained in detail in the description of the reference speed generation circuit 21, which will be described later.

In the routine 102, the control unit 2 further includes:
The access distance is set in the counter 16.

Next, in routine 103, the control section 2 turns on the acceleration command signal and sends it to the gate circuit 28.
By turning on the acceleration command signal, the gate of the gate circuit 28 is opened, and a constant acceleration voltage or acceleration current command signal given from the input line 27 is input to the power amplifier 3. The power amplifier 3 applies a voltage or current proportional to the accelerating voltage or accelerating current instruction signal to the actuator 4. As a result, the actuator 4 starts moving.

After executing the routine 103, the control unit 2 executes the routine 104, determines whether the access distance is larger than the first specified distance (first set distance set in advance), and if so, executes the routine 105. otherwise, routine 110 is executed.

If the access distance is larger than the first specified distance, the control unit 2 executes routine 105, and determines that the movement distance is half the value obtained by subtracting the second specified distance from the access distance (preset second setting). Determine whether the distance has been exceeded. This is position detection circuit 1
This is done by counting down the counter 14 using pulses generated by the moving distance detection circuit 18 based on the position of the actuator 4 detected in step 7, and monitoring by the control unit 2 when the contents of the counter reach 0. . If the moving distance exceeds half the value obtained by subtracting the second specified distance from the access distance, routine 106 is executed; otherwise, routine 105 is executed again.

In the routine 106, the control unit 12 turns off the acceleration command signal and closes the gate circuit 28, and
The gate circuit 31 is opened by turning on the deceleration command signal. As a result, a constant deceleration voltage or deceleration current instruction signal given from the input line 30 is input to the power amplifier 3 via the OR circuit 34, and the actuator 4 starts decelerating.

In routine 107, it is determined whether the speed of the actuator 4 has fallen below the standard speed. This is done by the control unit 12 determining whether the output of the comparison circuit 23 is "1" or not.

Here, the reference speed will be explained using the graph of FIG. 5. The residual distance is x _e and the acceleration of deceleration is α ₂
Then, the standard speed is given by √2 _{2 e} . The acceleration α ₂ of this deceleration is set to an acceleration that can be followed by closed-loop speed control, and is smaller than the acceleration α ₁ caused by the constant acceleration or deceleration instruction signal applied from the input line 27 or 30.

Further, the acceleration α 1 is set in advance so that the position where the actuator 4, which is decelerated by the acceleration α ₁ according to the constant deceleration instruction signal, matches the reference speed of √2 _{2 e} is at the point of the residual distance _{x s} . shall be taken as a thing.
In other words, the locus of the actuator 4 on the velocity-residual distance plane when deceleration continues until the velocity is zero at an acceleration α ₁ , and the locus of the standard velocity of √2 _{2 e} are the residuals as shown in Fig. 5. Intersect at a distance x _s .

When deceleration continues with acceleration α ₁ , if the residual distance at which the velocity becomes zero is x ₂ , the trajectory becomes v=√2 ₁ ( _e − ₂ ) on the velocity-residual distance plane. Since x _e = x _s and the two trajectories match as shown in Figure 5,
The following formula holds true.

v=√2 ₁ ( _e − ₂ )=√2 _{2 s} (2) From equation (2), the relationship between x ₂ and x _s can be found as follows.

x ₂ =(1−α ₂ /α ₁ )x _s (3) x ₂ given by equation (3) indicates the second specified distance. Furthermore, the access distance x ₁ when half of the value obtained by subtracting the second prescribed distance x ₂ from the access distance x ₁ is equal to the distance obtained by subtracting the residual distance x _s from the access distance x ₁ . It is given by the following formula.

x ₁ =2x _s −x ₂ =(1+α ₂ /α ₂ )x _s (4) x ₁ given by equation (4) indicates the first specified distance.

Now, in routine 107, if the speed of the actuator 4 falls below the standard speed, the process advances to routine 108; otherwise, routine 1
Repeat step 07.

In routine 108, the control unit 12 turns off the deceleration command signal to close the gate circuit 31, and turns on the loop control command signal to open the gate circuit 33. As a result, the output of the speed error detection circuit 2 is applied to the power amplifier 3, and the actuator 4 is decelerated by a voltage or current proportional to the speed error.

Thereafter, in routine 109, it is determined whether the output of the access completion condition detection circuit 37, which outputs "1" when the residual distance becomes zero, has become 1, and when it has become 1, the routine 112 is executed. the loop control command signal is turned off to complete the access.

Next, the operation in routine 104 when the access distance is smaller than the first specified distance will be described.

In this case, the control unit 2 executes the routine 110 and determines whether the speed of the actuator 4 exceeds the reference speed. This is done by monitoring the output of the comparison circuit 13 with the control section 2.
When the control section 2 detects in the routine 110 that the output of the comparison circuit 13 becomes "1", it executes the routine 111.

In routine 111, the acceleration command signal is turned off and the loop control command signal is turned on. As a result, the gate circuit 28 is closed, the gate circuit 33 is opened, the output of the speed error detection circuit 2 is applied to the power amplifier 3, and the actuator 4 is decelerated.

After executing the routine 111, the control unit 2 executes the routine 109. The operations after routine 39 are the same as those when the access distance is greater than the first specified distance, and are as described above.

FIG. 6 is a diagram showing signal waveforms of various parts when the access distance is 16 tracks according to this embodiment, in which a is the position waveform which is the output of the position detector 17;
b is the output waveform of the power amplifier 3, and c is the output waveform of the reference speed generation circuit 21 and the speed detection circuit 1. In FIG. 6, the setting values are as follows. In equations (2) and (3), if the residual distance x _s where the two standard velocity trajectories intersect is x _s = 4 tracks, and the ratio of acceleration α ₁ and α ₂ is α ₂ /α ₁ , then the first and Second
The prescribed distances x ₁ and x ₂ are respectively x ₁ = 6 tracks,
x ₂ = 2 tracks. Since the access distance is therefore greater than the first prescribed distance of 6 tracks, acceleration is carried out up to half of the access distance of 16 tracks minus the second prescribed distance of 2 tracks, i.e. 7 tracks, and then a switch is made to deceleration; When the residual distance reaches 4 tracks, the speed of the actuator 4 becomes equal to the standard speed, and from that point on, it is decelerated by a voltage or current proportional to the speed error, and access is completed when 16 tracks have been accessed. It has a waveform.

In addition, in the above operation, except for the closed-loop deceleration part due to speed error, the acceleration/deceleration part with a constant voltage or current is an open loop, so there is a decrease in the generated force near the end of the actuator's magnetic circuit, etc. , the access range B is limited by the variation in the generated force as shown in Figure 7, and after acceleration/deceleration with a constant voltage or current, the residual distance x _s (4 tracks in Figure 6) is as designed.
It is not always guaranteed that the speed of the actuator will be equal to the standard speed, and it may deviate by one or two tracks. If it deviates before the design value, it will not have any effect on the subsequent deceleration due to the speed error, but if it deviates after the design value, the deviation from the standard speed will become large due to the deceleration error caused by the subsequent speed error, even if the target track is reached. There is a possibility that the speed will not become zero and the vehicle will not be able to stop at the target position, resulting in an overshoot error. In order to avoid this, the design value of the residual distance x _s (4 tracks in Fig. 6) at which the actuator speed becomes equal to the reference speed can be increased to, for example, 6 tracks or 8 tracks. good. In any case, in the present invention, since the final stage of access is controlled in a closed loop based on a speed error, the structure is such that it is possible to absorb speed variations during open loop driving due to variations in the force generated by the actuator described above.

〔Effect of the invention〕

As explained above, according to the present invention, when the access distance of the actuator is larger than a predetermined distance, a constant acceleration voltage or acceleration current is applied to the actuator, and then a constant deceleration voltage or current is applied to the actuator. After the actuator's moving speed falls below a predetermined speed determined according to the residual distance, a voltage or current is applied to the actuator according to the difference between the standard speed and the actuator's moving speed, and the actuator's access distance is increased. If it is larger than the first set distance,
The actuator is accelerated and moved in an open loop, and when the moving distance of the actuator exceeds the second set distance, the moving speed is also decelerated in an open loop, and the moving speed of the actuator is adjusted according to the residual distance. When the speed drops below a predetermined reference speed, follow-up control is performed in a closed loop according to the difference between this reference speed and the movement speed of the actuator.
In addition, if the access distance of the actuator is smaller than the first set distance, the actuator is accelerated and moved in an open loop, and when the actuator movement speed reaches the reference speed or higher, follow-up control is performed in a closed loop. As a result, the speed can be controlled slowly in a closed loop only a short distance before the target position, and the remaining access distance can be driven with the maximum force that the actuator can generate, thereby speeding up the access time.
In other words, when comparing the same access distance, conventional tracking control is performed in a closed loop from the beginning, so when the access distance is long, it takes a long time to access the target position from the start of control, but in the present invention, The actuator is driven in an open loop by applying a constant input to the actuator, accelerating at a higher speed than before, then decelerating rapidly and quickly driving close to the target position.
After the moving speed reaches the standard speed, follow-up control is performed in a closed loop to stop at the target position, so the access time from the starting point to the target position can be shorter than before, and high-speed movement is possible.

[Brief explanation of drawings]

FIG. 1a is a block diagram when a conventional access control method is used, FIG. 1b is a characteristic diagram thereof, FIG. 2 is a block diagram showing an embodiment of the present invention, and FIG. An output waveform diagram, FIG. 4 is a flowchart showing the operation, FIG. 5 is a diagram showing a standard speed curve, and FIG. 6 is a waveform diagram when the actuator is operated using an embodiment of the present invention. FIG. 7 is a diagram showing variations in the force generated by the actuator. 1...Speed detector, 2...Speed error detection circuit,
3... Power amplifier, 4... Actuator, 1
2...Control unit, 14, 16...Counter, 17...
...position detection circuit, 18...movement distance detection circuit, 2
0... Residual distance detection circuit, 21... Reference speed generation circuit, 23... Comparison circuit, 28, 31, 33...
Gate circuit, 34... OR circuit, 37... Access completion condition detection circuit.

Claims (1)

[Claims] 1. An actuator stopped at a certain position,
In the access control method of moving and stopping at a position separated by an access distance that is an arbitrary specified distance, if the access distance of the actuator is larger than a first set distance, a constant accelerating voltage or accelerating current is applied to the actuator. The actuator is moved by open-loop drive by giving
When the movement distance of the actuator exceeds a second set distance, a constant deceleration voltage or deceleration current is applied to reduce the movement speed of the actuator by open-loop driving, and as a result of this deceleration, the movement speed of the actuator becomes When the speed exceeds a reference speed predetermined according to the residual distance, which is the distance obtained by subtracting the actual movement speed of the actuator from the access distance, the speed is adjusted according to the difference between this reference speed and the movement speed of the actuator. applying a voltage or current to the actuator to perform follow-up control in a closed-loop drive, stopping the actuator at the target position, and adjusting the access distance of the actuator to the first position.
If the distance is smaller than the set distance, apply a constant accelerating voltage or accelerating current to the actuator to move the actuator in open loop drive, and when the moving speed of the actuator reaches or exceeds the reference speed, this reference An access control method for an actuator, characterized in that the actuator is stopped at a target position by applying a voltage or current to the actuator according to the difference between the speed and the moving speed of the actuator to perform follow-up control in a closed loop drive.