JPH0697058B2 - Control method for cylinder with braking device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a control method for a cylinder with a braking device.

PRIOR ART Cylinders with a braking device for braking the movement of a piston rod are known.

In a conventional cylinder, a method of fitting an eccentric cam to a piston rod and applying a force to eccentrically move the piston rod in the radial direction by the rotation of the cam to perform friction braking has been adopted.

In the conventional cylinder with the braking device, the braking force is continuously applied and the friction braking is repeated, but there is a problem in the repeating accuracy.

Object The present invention solves the above conventional problems and aims to provide a smooth and accurate control method.

Configuration The present invention has the above object of intermittently applying a voltage to a plurality of ring-shaped electrostrictive elements fitted in a piston rod and juxtaposed in the axial direction in a pulsed manner for a predetermined time from a voltage application device. The present invention is achieved by a control method characterized in that the piston reciprocating at a constant speed is gradually braked or released to accelerate and decelerate the piston.

The details of the configuration and operation of the present invention will be described based on the embodiments shown in the drawings.

In FIGS. 1 and 2, a piston 2 is slidably accommodated in a cylinder tube 1, and a piston rod 3 fixed to the piston 2 penetrates a rod cover 4 fixed to the cylinder tube 1 and protrudes to the outside. ing. The piston 2 is reciprocated by alternately supplying and discharging the pressurized liquid to and from the inlet / outlet 5 formed in the rod cover 4 and the inlet / outlet 7 formed in the head cover 6 fixed to the cylinder tube 1.

A braking device 9 is housed in a brake casing 8 fixed to the rod cover 4.

The braking device 9 is fitted on the cylindrical brake shoe 10 fitted on the piston rod 3, and a plurality of ring-shaped electrostrictive elements 11 fitted around the cylindrical brake shoe 10 and arranged in layers in the axial direction of the piston rod. And an electrode 12 formed between the electrostrictive element, electric wires 13 and 14 connected to the electrode 12, and the electric wire 1
And a voltage applying device 15 connected to the terminals 3 and 14.

The cylindrical brake shoe 10 preferably has a slit 16 so that the tightening force on the piston rod 3 can be easily changed by radial deformation. The slit 16 may be a single slit extending in the axial direction, or a plurality of slits may be arranged in a zigzag pattern, and any shape may be appropriately selected as long as it has a shape that easily contracts in the circumferential direction. In some cases, the cylindrical brake shoe 10 may be omitted and the ring-shaped electrostrictive element may be used also as the brake shoe.

The electrodes 12 between the electrostrictive elements 11 are alternately divided into those connected to the (+) pole of the voltage applying device by the electrodes 14 and those connected to the (-) pole of the voltage applying device 15 by the electric wire 13. Each electrostrictive element 11 is formed with a recess 17 through which the electric wire 13 can be passed and a recess 18 through which the electric wire 14 can be passed in a part of the peripheral edge.

While the inner circumference of the brake shoe 10 or the electrostrictive element 11 and the outer circumference of the piston rod 3 are formed into a cylindrical shape that fits with each other, the brake shoe 10 or the electrostrictive element is formed in a polygonal shape as shown in FIG. It is also possible to prevent relative rotation between 11 and the piston rod 3.

The braking device 9 is usually fitted loosely on the piston rod 3 and uses an electrostrictive element 11 formed to ensure free rotation of the piston rod 3, and a voltage is applied by a voltage application device 15 when braking is desired. The electrostrictive element 11 may cause contraction strain to tighten the piston rod 3 directly or through the brake shoe 10, but on the contrary, the brake shoe 10 is normally tightened to tighten the piston rod 3. Using an electrostrictive element 11 that is fitted tightly, applying a voltage causes expansion strain in the electrostrictive element 11 to release the tightening force on the piston rod 3 so that the piston rod 3 can freely rotate. You can also do it. In the latter case, since the braking action is performed when there is no voltage, it is convenient when it is desired to prevent the piston rod from moving during a power outage, a factory suspension, etc., and acts as a safe brake.

As an electrostrictive element, a piezoelectric actuator formed by laminating and bonding ceramic thin plates is known.

Since the electrostrictive element has the characteristics of large output and small deformation, it is most suitable for the above braking device.

While the voltage application device of the braking device directly applies a predetermined voltage to switch between the braking state and the braking release state, when the braking start and the braking release are gradually performed, the speed of the piston rod increases. Since it changes gradually, the accuracy of the stop position can be improved. As a specific example thereof, as shown in FIG. 4, in the braking state, the voltage is applied in a pulse form for a short time. As a result, the electrostrictive element 11 gradually generates a strain each time a voltage is applied, and gradually weakens the braking force. As the braking force weakens, the piston rod 3 starts to move while resisting the braking resistance by the force applied to the piston 2, and gradually increases in speed, and after a predetermined time, that is, after a predetermined number of pulsed voltage applications are repeated, the voltage is applied All the strain elements 11 are completely strained, the braking force is released, and the piston rod 3 moves at a constant speed. Similarly, when the motor is stopped, the voltage is applied in a pulsed manner for a short time, the braking force is gradually applied, the speed of the piston rod 3 is reduced, and the full braking state is reached after a predetermined time. Since the piston rod is not suddenly stopped and is hardly affected by inertia, the stop position is maintained at a position which is almost accurately determined.

As a control method when the brake is applied and when the brake is released, as shown in FIG. 5, it is possible to instruct the start of control and the end of braking, and the start of braking and the end of brake release, respectively, by microswitches. A switch actuating portion 20 is provided on the piston 3 so that the switch actuating portion 20 operates at the retracted end position of the piston 3; The preliminary deceleration end position instruction switch 24 is arranged at a predetermined position. Each switch 21, 22,
Each of 23 and 24 is electrically connected to a control device 25 including a voltage applying device.

Under the operation of the switch actuation unit 20 of the pre-acceleration start position instruction switch 21, a voltage is applied from the voltage application device to the braking device 9 by a signal from the control device 25, and the braking is released. When releasing the braking, first, a voltage is applied as a pulse in the preliminary acceleration region to gradually release the braking. By gradually releasing the braking, the piston 3 gradually increases in speed. When the actuating portion 20 of the piston 3 actuates the pre-acceleration end position indicating switch 22, a constant voltage is applied and the braking release state is maintained. When the piston 3 comes to a position a predetermined distance before the stop position, the actuation unit 20 actuates the preliminary deceleration start position instruction switch 23, and the pulsed voltage application is started. That is, the release of the applied voltage to the braking device is started. When the voltage is intermittently applied in a pulsed manner for a short time to reduce the applied voltage to the braking device, the braking device gradually increases the braking action and gradually brakes the piston 3. At the position where a predetermined time has elapsed after the start of braking, the actuating member 20 actuates the preliminary deceleration end position indicating switch 24, and the control device 25 releases the voltage application to the braking device. As a result, the braking device 9 completely brakes the piston 3 and stops it.

When the piston 3 can be retracted, the reverse operation is performed exactly as described above.

As a modified example of the control method, servo control can be performed as shown in FIG. The piston 3 has a position detector 26
Is provided to detect the moving position of the piston 3. The position detection device 26 is electrically connected to the comparison calculation unit 27. The comparison calculation unit 27 is formed so as to input information on the target position where the piston 3 stops. The comparison calculation unit 27 is connected to the control device 25.

The braking device 9 is configured similarly to the above so that the braking operation is performed when no voltage is applied and the braking is released when a voltage is applied. When the moving piston 3 reaches a predetermined position, a voltage is applied in a pulsed manner by a signal obtained by a comparison calculation of target position information and current position information. The pulse width of the voltage in that case is modulated according to the comparison calculation value. That is, the pulse width is large when it is distant from the target position, and the pulse width is set to be gradually shortened as it approaches the target position. Thus, the pulse width of the applied voltage is set to 0 when the target position is reached.

Although the example in which the braking operation is performed at the time of no voltage is shown, conversely, the braking may be released at the time of no voltage. In this case, the non-voltage pulse width becomes 0 at the target position.

Effects Generally, an oil film, dust or the like adheres to the piston rod of the cylinder, the frictional force is not stabilized due to the inclusion of the adhered substance, and it is difficult to accurately control the braking force. This state is remarkable when the braking force is moderate, and when the braking force is strongly applied, the inclusions are made uniform or eliminated, and are relatively stable. The present invention avoids this moderate state by the voltage pulse control and obtains a smooth and stable braking effect. The braking force is gradually increased with each pulse, and the overall braking effect can be enhanced by controlling the dwell time. As a result, the stopping accuracy and acceleration accuracy of the cylinder can be stabilized, and the performance as an actuator can be significantly improved.

Moreover, the frequency of pulse control could be increased to a practical range by using the brake actuation method using an electrostrictive element. In other words, it enables high-speed switching, which was impossible in the past.

[Brief description of drawings]

FIG. 1 is a sectional view of a cylinder according to the present invention, and FIG.
II-II sectional drawing of the figure, FIG. 3 is a figure which shows the modification of the piston rod and brake shoe in FIG. 2, FIG. 4 is a figure which shows an example of a voltage application state, FIG. 5 is an example of a brake control method. FIG. 6 is a diagram showing another example of the brake control method. 3 ... Piston rod, 9 ... Braking device 10 ... Brake shoe, 11 ... Electrostrictive element 15 ... Voltage applying device, 25 ... Control device 26 ... Position detecting device, 27 ... Comparative computing device

Claims (3)

[Claims] 1. A voltage applying device intermittently applies a voltage to a plurality of ring-shaped electrostrictive elements fitted in a piston rod and juxtaposed in the axial direction in a pulsed manner for a predetermined time.
A method for controlling a cylinder with a braking device, which comprises accelerating and decelerating a piston that reciprocates at a constant speed by gradually braking or releasing the piston. 2. The method for controlling a cylinder with a braking device according to claim 1, wherein the voltage applied in a pulsed manner is applied as a pulse width modulated voltage. 3. The method for controlling a cylinder with a braking device according to claim 1, wherein the pulse width of the voltage is selected by a comparison calculation of target position information and current position information.