JPH0221001A - Accurate positioning method for pneumatic cylinder - Google Patents

Abstract

PURPOSE:To perform the accurate positioning of a piston by functioning a braking mechanism to stop the piston at a position a constant distance before its target stop position, and releasing air pressure from a room on one side to stop the piston at the target position. CONSTITUTION:A braking mechanism 4 is functioned to stop a piston 2 within a range of + or -0.5mm when the piston 2 approaches its target position, and a directional control valve 11 is set in its neutral position for making both rooms C1, C2 of a cylinder 1 in pressurized condition. Then, an on-off valve 18 is pulsatively operated to gradually release the hydraulic pressure inside the room C2, and simultaneously to release the braking mechanism 4 for moving the piston 2 at a crawling speed. The piston 2 puts the on-off valve 18 off when it reaches the target value for stoppage, and actuates the braking mechanism 4 to stop the piston 2. Thus, the accurate positioning of the piston 2 is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a method for positioning a pneumatic cylinder with high precision.

(B) Prior Art Various devices have been proposed in the past for arbitrarily stopping the piston of a pneumatic cylinder midway through its full stroke. One such conventional device is the one described in Japanese Patent Application Laid-Open No. 52-67479. This conventional device decelerates the piston by applying a braking force to the piston by introducing fluid pressure of the same pressure into the chambers on both sides of the piston before the piston reaches the desired stopping position. The piston is finally stopped by a mechanical braking device.

In the positioning method performed by conventional devices including the device described in the above-mentioned publication, the intermediate stop precision is approximately ±0.1 mm at most, and cannot be used for the purpose of precise positioning. For this reason, pneumatic cylinders were only used for the full stroke or for rough intermediate stops.

By the way, the present inventor conducted various experiments and investigated the operation of a pneumatic cylinder at the initial stage of piston startup, that is, the relationship between the position and speed of the piston, and found that when the piston is started, especially when the piston displacement is 0.5 mm or less, We found that the speed was extremely low in some cases. That is,
It has been found that there is a relationship as shown in FIG. 3 between the position and velocity of the piston when the pneumatic cylinder is activated. The figure is a graph showing representative results of multiple measurements, and as is clear from the figure, when the piston starts moving, when the piston displacement is within 0.5 mm, compared to when it is more than 0.5 mm, it is clear that Piston speed is 0.5mm
/sec, which is extremely low. The present invention utilizes exactly this property of the cylinder.

(c) Problems to be solved by the invention The problems to be solved by the present invention are to utilize the above-mentioned properties of the cylinder to stop the piston very close to the stop target using a lock-up brake mechanism. Precise positioning of the piston is achieved by slightly moving the piston by disrupting the pressure balance in the chambers on both sides of the piston.

Another object of the present invention is to improve positioning accuracy by using both a position detection sensor with relatively coarse resolution for long strokes and a sensor with high resolution for short strokes.

(d) Means for solving the problem In order to solve the above problem, one invention of the present application provides a pneumatic cylinder equipped with a sensor that detects the position of a piston and a lock-up brake mechanism that stops the piston at a desired position. In the precision positioning method, the lock-up type brake mechanism applies a brake to the piston from a certain distance before the stop target, and temporarily stops the piston within about ±0.5 mm of the stop target, and then After the pressure in the chamber is balanced, the chamber on the stop target side is sealed, and after the operation of the brake mechanism is released, the air pressure in the chamber on the stop target side is slightly released to cause the piston to move slightly. Immediately before the detected stop target, the brake mechanism is operated again to apply a brake to the piston.

Another invention of the present application is that in the above invention, a long stroke sensor with relatively coarse resolution and a short stroke high resolution sensor dedicated to the vicinity of the stop target are used together.

(e) The piston and piston rod are temporarily stopped by a lock-up brake mechanism at a position close to the action stop target, and then moved at a very slow speed using the unbalance of pressure in the chambers on both sides of the piston, and then stopped by the brake mechanism. Therefore, the piston and piston rod can be precisely positioned.

(F) Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

In FIG. 1, an example of an apparatus for implementing the precision positioning method of the present invention is shown. In the figure, 1 is a cylinder, 2 is a piston of the cylinder, 3 is a piston rod, and 4 is a brake mechanism that mechanically applies a brake to the piston rod 3, and a spring (not shown) is used when air pressure is not supplied. This is a lock-up type brake mechanism with a known structure that applies the brakes using the following methods. A magnetostrictive vibration type position sensor 6 is connected to the piston rod 3.

This magnetostrictive vibration type position sensor has a known structure including a ring magnet 7 attached to a one-stone rod 3 and a sensor probe 8 that engages with the ring magnet.

Cylinder l is connected to a pneumatic control circuit 10. This pneumatic control circuit IO includes a directional control valve 11 connected to a pneumatic pressure source P, a brake on-off valve 12 connected between the pneumatic pressure source P and a lock-up brake mechanism of a cylinder l, and a directional control valve 11 A regulator 13 and a speed controller 14 connected between one port of the cylinder 1 and a chamber C8 on one side of the cylinder 1 (on the left side of the piston in the figure);
The other port of the directional control valve 11 and the other chamber C of the cylinder 1
2, a speed controller 17 connected in parallel to the second on-off valve 12, and a third on-off valve 17 connected in series to the other chamber C2 of the cylinder l. The on/off valve 18 and speed controller 19 are provided.

Further, the sensor probe 8 of the position sensor 6 includes a pulse width-voltage converter 21, an A/D converter 22, and a computer 2.
3 is connected.

In the above configuration, in the initial state, the on/off valve 12 for the brake mechanism is turned off, and the piston rod 3 is engaged with the brake mechanism 4 and locked. On the other hand, the directional control valve 11 is in the neutral position, the first and second on-off valves 15 and 16 are on, and the third on-off valve 18 is on.
is turned off. Therefore, air pressure from the air pressure source P is simultaneously supplied to the chambers C1 and C2 on both sides of the cylinder 1. At this time, the air pressure in the chamber CI is made lower than the air pressure in the chamber C2 by the regulator 13 in accordance with the difference in the area of action of the air pressure in the room, and the forces acting on both surfaces of the piston 2 are balanced.

When operating the cylinder 1 to move the piston 2 and piston rod 3 at high speed, first, the solenoid 12a of the on-off valve 12 is energized and operated.

Then, air pressure from the air pressure source P is supplied to the brake mechanism 4, releasing the brake acting on the piston rod. Furthermore, one solenoid ll of the direction control valve 11
When energized, one chamber C1 of the cylinder 1 remains in communication with the source of air pressure P, while the other chamber C2 is opened to the atmosphere.

Therefore, air pressure is supplied to chamber C1 and air pressure is discharged from chamber C2 via on-off valves 15 and 16, causing piston 2 and piston rod 3 to rapidly move to the right (in FIG. 1). The movement of the piston rod 3 is measured by the position detection sensor 6, and the information is input to the computer 23 via the A/D converter 22. When the position of the piston rod 3 approaches the stop target, that is, the target stop position, the energization to the solenoid 16a of the on-off valve 16 is stopped in response to a command from the computer 23, and the solenoid 16a is turned off.

Therefore, the air pressure discharged into the atmosphere from the chamber C2 is passed through the speed controller 17 and throttled, and the piston and piston rod are decelerated.

When the target stop position is further approached, the energization of the solenoid 12a of the on-off valve 12 is stopped and turned off, air pressure is discharged from the brake mechanism 4, the brake is operated, and the piston rod is stopped.

In this case, the piston 2 and the piston rod 3 are controlled while detecting their positions with a position sensor so as to stop within a range of approximately ±0.5 mm from the target stop position.

Next, with the brake mechanism 4 applying a brake to the piston rod, the energization to the solenoid lla of the directional control valve 11 is stopped to turn it off to bring it to the neutral position. Both chambers C1 and C2 of cylinder l are then connected simultaneously to a fluid source and become a pressurized layer, and the forces acting on both sides of the piston are balanced, as before.

Therefore, the next step is to stop energizing the solenoid 15a of the on-off valve 15 and turn it off, thereby closing the chamber C2.

In this state, the on-off valve 12 is turned on and the brake mechanism 4
Even if the piston and piston rod are released, the piston and piston rod remain stopped.

Next, when the solenoid 18a of the on-off valve 18 is activated in a pulsed manner, the fluid pressure in the chamber C2 is gradually released into the atmosphere. As a result, the fluid pressure in chamber C2 becomes slightly lower than the fluid pressure in chamber C4, and the balance of forces acting on both sides of the piston is disrupted, causing the piston and piston rod to move at a slight rate of about 0.5 mm/sec. Start moving at speed.

While the piston 2 and piston rod 3 are moving at a very slow speed, the position detection sensor 6 detects whether the piston 2 or the piston rod 3 is
When it is detected that the solenoid of the on-off valve 12 has arrived at the target stop position, the power to the solenoid of the on-off valve 12 is immediately cut off, the on-off valve is turned off, and the brake mechanism 4 applies a brake force to the piston rod, causing the piston rod and piston to Stop it instantly.

At this time, accuracy can be further improved by making fine adjustments so that the brake operation is performed slightly before the target stop position, with a certain delay in the brake operation time.

By repeating the above operations, the stopping position of the piston and/or piston rod is precisely controlled.

The above control sequence can be expressed as a flowchart as shown in FIG. 2.

[Test Example 1] Using a pneumatic cylinder with a full stroke of 300+ ohm,
As the position detection sensor, we adopted a method that detects the position of the ring magnet using a sensor probe built into a magnetostrictive tube. Also, the output is a DC analog output, and changes from Ov to IOV over a full stroke of 300mm. Since a 12-bit A/D converter was used, the resolution of the sensor was 73 μm.

Under these conditions, the stopping position is 100i+m5150m
When the test was repeated 50 times for each length of m and 200 mm, the results were obtained as shown in graphs in FIGS. 3 to 5, respectively. In this graph, the vertical axis indicates the value obtained by A/D converting the output of the position detection sensor.
The quantization unit of D conversion is 73 μm), and the position indicated by the mouth on the vertical axis is the target stop position. The point plotted with I;, Δ is the stopping position due to the first brake, and the point plotted with O is the stopping position due to the second braking.

As is clear from the above graph, the variation in the stopping position due to the first brake is 511μ, whereas the variation in the stopping position due to the first brake is 2
The variation in the final stopping position due to the second brake is 146
Jm, indicating that highly accurate positioning is possible.

In FIG. 6, a circuit diagram is shown in which a high-resolution differential transformer 9 is also used as a position detection sensor for position control. Incidentally, since the fluid pressure circuit for driving the cylinder and its operation are the same as in the previous embodiment, a detailed explanation thereof will be omitted, and only the test results will be shown below.

[Test Example 2] The differential transformer used in this test had a linearity of 0.77%.
(Output voltage 0 to 1OV at full stroke 8.5mm)
As a result of calibrating the part used in the test, the resolution was 1.9 μm.

Under these conditions, the target stopping position is I OO+am
.

The first braking position was 95.2mm (overrun was estimated to be 4.8mm), the second braking position was 99.998n+m (overrun was estimated to be 2μ), and the test was repeated 200 times. However.

The results are now shown in Tables 1 and 2.

Table 1 Stop position (mm) +o.

Stopping error (μm) -1,90+1.9 +
3.11 degrees (total 200) 7 119
73 1 Table 2 Average stopping position (mm) Deviation (μm) Standard deviation, -
I (μm) 1 step stop 99.647
1102 step stop 100.0006
+0.6 1 As is clear from these tables, the stopping accuracy was able to be improved by increasing the resolution of the position detection sensor. Moreover, the stopping error is -
1.9~+3.8j1m.

It is clear that very good results can be obtained with a standard deviation of 1 μm.

[Test Example 3] The above two test examples were conducted under no-load conditions;
In this test, an inertial load of 10 kg was applied. Note that the control device was the same as in Test Example 2. The results of this test are shown in Tables 3 and 4.

Table 3 Stop error -3,8-1,90,0+1.9 +5.
7 +7.6 +9.5 degree (200) 3
26! H511633 Stop error +11.4
... +17.1 ... +26.6 Frequency 1 ... 1 ... 1 Table 4 Average stopping position (related) Deviation (μm) Standard deviation, -1
(μm) 1st step stop 99.784110 2nd step stop ・100.0009 +0.9
3 As is clear from the above table, the effect of applying a load is that while the standard deviation in the case of no load is 1 μm, the standard deviation of the standard deviation in the case of no load increases to 3J+a, and the deviation is also +0 in the case of no load. What was .6 μm became +0.9, which is an increase in both cases. This is thought to be because the kinetic energy of the inertial load increases when the load is applied.

However, since kinetic energy is proportional to the square of velocity, the influence is small in the method of the present invention, which utilizes times when the kinetic velocity is very low.

In this embodiment, it has been explained that the magnetostrictive vibration type sensor 6 and the high-resolution differential transformer 9 are used together as the position detection sensor, but it is of course possible to use an optical type, electromagnetic type or other position sensor. 1 or a position sensor built into the piston rod 3.

(g) Effects According to the present invention, the following effects can be achieved.

■Precise positioning of pneumatic cylinders is possible and is inexpensive (
It is possible to manufacture a precision feeding table that is more precise than the pole screw pulse motor method.

Since the robot can be stopped at the target stop position with an error of less than 0.010 μm, precision robots can be driven.

■Can be applied to drive devices in semiconductor processes.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an apparatus for carrying out the precision positioning method of a pneumatic cylinder of the present invention, FIG. 2 is a flowchart of the control sequence of the apparatus of FIG. 1, and FIGS. 3 to 5 are A graphical diagram showing the test results, FIG. 6 is a diagram showing another apparatus for carrying out the positioning method. 1 Niji cylinder 2: Piston 3: Piston rod 4 Nibble mechanism 6: Position detection sensor 11: Directional control valve 12.15.16.18:
On-off valve i standing JI? J>@, 15 (700m-) book 4, pregnant, 5

Claims (1)

[Claims] 1. In a method for precision positioning of a pneumatic cylinder equipped with a sensor that detects the position of a piston and a lock-up brake mechanism that stops the piston at a desired position, the lock is set from a certain distance before the target stop position. The up-type brake mechanism applies a brake to the piston to temporarily stop the piston within approximately ±0.5 mm of the stop target, and after the piston stops, the pressure in the chambers before and after the piston is balanced, and then the chamber on the stop target side After sealing and releasing the operation of the brake mechanism, the piston is slightly moved by slightly releasing the air pressure in the chamber on the side of the stop target, and the brake mechanism is operated again just before the stop target detected by the sensor. A method for precisely positioning a pneumatic cylinder, the method comprising: applying a brake to the piston. 2. The method for precisely positioning a pneumatic cylinder according to claim 1, which uses, as the sensor, a long stroke sensor with relatively coarse resolution and a short stroke high resolution sensor dedicated to the vicinity of the stop target.