WO2006070998A1

WO2006070998A1 - Pneumatic cylinder using elastic rubber and system and method for controlling position of pneumatic cylinder

Info

Publication number: WO2006070998A1
Application number: PCT/KR2005/003803
Authority: WO
Inventors: Bong Sueg Kim; Jung Gyu Park
Original assignee: Z. Tec. Co. Ltd.
Priority date: 2004-12-30
Filing date: 2005-11-10
Publication date: 2006-07-06
Also published as: KR100553253B1; CN100507788C; CN101061445A

Abstract

Provided is a pneumatic cylinder using elastic rubber used for an alignment apparatus or a centering apparatus of a board. The pneumatic cylinder includes a cylinder cover protecting a cylinder head, a fixing bracket having an air injection hole to inject air, elastic rubber having a hemispheric shape, fixed in the cylinder cover with respect to the air injection hole of the fixing bracket, and expanding and contracting according to a change in the amount of compressed air that is supplied and exhausted through the air injection hole, a piston rod penetrating the cylinder cover and advancing and retreating according to a change in the amount of the expansion and contraction of the elastic rubber, a spring installed at the piston rod and allowing the piston rod to advance and retreat according to the expansion and contraction of the elastic rubber, a sliding bearing guiding a linear motion of the piston rod, a sliding bearing support bracket supporting the sliding bearing, a displacement sensor measuring the displacement of the piston rod, a sensor dog transferring the displacement of the piston rod to the displacement sensor, and a fixed plate on which the fixing bracket, the cylinder cover, and the sliding bearing support bracket are fixedly installed.

Description

PNEUMATIC CYLINDER USING ELASTIC RUBBER AND SYSTEM AND METHOD FOR CONTROLLING POSITION OF

PNEUMATIC CYLINDER

Technical Field

[1] The present invention is related to a pneumatic cylinder used for an aligning apparatus or centering apparatus for a board and a system and method of controlling the position of the pneumatic cylinder, and more particularly, to a pneumatic cylinder using elastic rubber which can accurately perform a position control with a small force by minimizing friction and controlling the pressure of air that is supplied to a low pressure, and to a system and method of controlling the position of the pneumatic cylinder.

Background Art

[2] FlG. 1 shows a conventional pneumatic cylinder and a system for controlling the position of the pneumatic cylinder. Referring to FlG. 1, the conventional pneumatic cylinder has two chambers which are divided by a cylinder tube 12 and a piston head 13. The piston head 13 is moved by a difference in pressure between two chambers and a predetermined job is performed as a piston rod 10 connected to the piston head 13 moves.

[3] A piston head cover 11 and a cylinder head cover 14 maintain a stroke distance that the piston rod 10 moves. Air injection holes 11a and 14a are installed at the piston head cover 11 and the cylinder head cover 14, respectively. As compressed air is injected into or exhausted from the two chambers through the air injection holes 11a and 14a. Thus, a difference in pressure is generated between the chambers so that the piston head 13 is moved.

[4] A pair of limit switches 15a and 15b are used to check whether the piston head 13 arrives at a desired position. When the limit switches 15a and 15b input signals to a controller 16 via an input port 16b, by a preset program of the controller 16, a signal of the limit switch 15a is generated when the piston head 13 is located at the side of the cylinder head cover 14 and a signal of the limit switch 15b is generated when the piston head 13 is located at the side of the piston head cover 11. Thus, the position of the piston head 13 is recognized according to the signals so that a control signal of a 5-port, 2-position solenoid valve 17 is output via an output port 16a.

[5] When the piston head 13 is located at the side of the cylinder head cover 14, the solenoid valve 17 is operated to supply compressed air 19 through the air injection hole air injection hole 1 Ia of the piston head cover 11 is exhausted to the outside through a speed control value 18a. The speed at which the piston rod 10 advances is controlled according to the amount of air controlled by the speed control valve 18a.

[6] When a signal is input to the limit switch 15a, the piston head 13 is recognized to move toward the piston rod 10. The compressed air 19 is injected through the air injection hole 1 Ia of the piston head cover 11 so that the piston rod 10 retreats by turning the solenoid valve 17 off. The compressed air in the chamber connected to the air injection hole 14a of the cylinder head cover 11 is exhausted to the outside through the speed control valve 18b. Thus, the retreating speed of the piston rod 10 is controlled by the speed control valve 18b.

[7] As described above, the piston rod 10 reciprocates the stroke distance that is determined by the configuration of the cylinder and is stopped by the piston head cover 11 and the cylinder head cover 14. A factional force is generated by a material such as an oil ring used to prevent leakage of air between the cylinder tube 12 and the piston head 13. The frictional force makes the positional control difficult so hath the motion of the piston head 13 needs to be mechanically stopped using a stopper. Thus, the conventional pneumatic cylinder is widely used in a system in which a stroke is fixed or a system requiring a simple repetitive job.

[8] Although the conventional pneumatic cylinder is widely used as a constituent element of an automated system, precise positional control for locating and keeping a piston head at a desired position is impossible due to the effect by the frictional force between the piston head and the cylinder tube. Therefore, although having a feature of easy control with a small force by controlling the air pressure, the conventional pneumatic cylinder is difficult to be applied to the aligning apparatus or centering apparatus for a board which requires direct operation. Disclosure of Invention

Technical Problem

[9] To solve the above and/or other problems, the present invention provides a pneumatic cylinder using elastic rubber to reduce a frictional force to be used for a board aligning apparatus or centering apparatus so that accurate position control can be performed by directly pushing and pulling a board with a small force and a defective rate is reduced in checking and processing steps and productivity is improved, and to a system, and a system and method of controlling the position of the pneumatic cylinder

Technical Solution

[10] According to an aspect of the present invention, a pneumatic cylinder using elastic rubber used for an alignment apparatus or a centering apparatus of a board comprises a cylinder cover protecting a cylinder head, a fixing bracket having an air injection hole to inject air, elastic rubber having a hemispheric shape, fixed in the cylinder cover with respect to the air injection hole of the fixing bracket, and expanding and contracting according to a change in the amount of compressed air that is supplied and exhausted through the air injection hole, a piston rod penetrating the cylinder cover and advancing and retreating according to a change in the amount of the expansion and contraction of the elastic rubber, a spring installed at the piston rod and allowing the piston rod to advance and retreat according to the expansion and contraction of the elastic rubber, a sliding bearing guiding a linear motion of the piston rod, a sliding bearing support bracket supporting the sliding bearing, a displacement sensor measuring the displacement of the piston rod, a sensor dog transferring the displacement of the piston rod to the displacement sensor, and a fixed plate on which the fixing bracket, the cylinder cover, and the sliding bearing support bracket are fixedly installed.

[11] According to another aspect of the present invention, a system of controlling the position of the above pneumatic cylinder using elastic rubber comprises an air input valve module supplying compressed air through the air injection hole to allow the piston rod to advance, an air output valve module exhausting the compressed air in a chamber defined by the elastic rubber and the fixing bracket to the outside through the air injection hole to allow the piston rod to retreat, a control unit having a controller which receives a signal of the displacement sensor through an input port, compares information obtained from the signal with a target value to generate a positional error, and calculates the opening and closing time of a solenoid valve using a value of the positional error, and outputting a control signal of the controller through an output port, and a valve driving unit receiving the control signal of the controller and controlling the air input and output valve modules.

[12] According to yet another aspect of the present invention, a method of controlling the position of the above pneumatic cylinder using elastic rubber comprises (a) measuring the displacement of the piston rod which changes according to the change in the amount of the compressed air supplied to the elastic rubber, using the displacement sensor contacting the sensor dog, inputting the measured displacement to an input port included in a control unit via a signal processor, and converting the measured displacement into a digital valve by an A/D convert, (b) generating a positional error by comparing the converted digital valve passing a measurement portion with a target valve set by a user in advance, (c) determining whether the generated positional error has a negative value or a positive value to operate a solenoid valve of an air output valve module and a solenoid valve of an air input valve module, and (d) when the positional error is generated, calculating operation time of the solenoid valve using the positional error, transferring the calculated operation time of the solenoid valve to the valve driving unit via an output port, and controlling the solenoid valve by transmitting an air input signal or an air output signal to each of the solenoid valves according to the air input or output determined by the sign of the positional error at the valve driving unit.

Description of Drawings

[13] FlG. 1 is a cross-sectional view of a conventional pneumatic cylinder and a system for controlling the position of the pneumatic cylinder;

[14] FlG. 2 is a cross-sectional view of a pneumatic cylinder using elastic rubber according to an embodiment of the present invention;

[15] FlG. 3 is a view showing a system for controlling the position of the pneumatic cylinder of FlG. 2; and

[16] FlG. 4 is a view showing the flow of a signal in the system of FlG. 3.

Mode for Invention

[17] FlG. 2 is a cross-sectional view of a pneumatic cylinder using elastic rubber according to an embodiment of the present invention. Referring to FlG. 2, a chamber formed by an elastic rubber 27 and a fixing bracket 25 for fixing the elastic rubber 27 is provided to remove an effect by a factional force generated between a piston head and a cylinder tube. That is, the amount of compressed air passing through an air injection hole 25a causes deformation of the elastic rubber 27 so that a force to advance a piston rod 31 is generated. The advanced piston rod 31 is returned by the elasticity of the piston rod 31 that is installed between the elastic rubber 27 and a cylinder cover 23.

[18] The pneumatic cylinder according to the present invention can be attached to other element by means of a fixed plate 26 on which the fixing bracket 25, the cylinder cover 23, and a sliding bearing support bracket 34 are fixedly installed. The piston rod 31 repeatedly advances and retreats as the elastic rubber 27 is deformed and a displacement generated thereby is transferred to a displacement sensor rod 21c by a sensor dog 22. According to the motion of the displacement sensor rod 21c, a displacement sensor 21a generates a voltage in proportional to the displacement sensor rod 21c.

[19] Since the voltage of the displacement sensor 21a is proportional to the movement distance of the piston rod 31, a positional error is generated by converting the voltage to a position and comparing the converted voltage with a target value so that determination of a precise position is possible by performing a positional servo control. Since the piston rod 31 advances by the elastic rubber 27 and is returned by a spring 29, a viscosity frictional coefficient becomes insufficient so that vibration may be generated. To reduce the vibration, a fluid damper 30 is installed on the fixed plate 26 so that the lower portion of the sensor dog 22 is sunk under viscosity fluid.

[20] In some case, without using the fluid damper 30, by adding a differential control function formed by differentiating a positional error generated by the difference between a target value and an actual displacement measured by the displacement sensor 21a inside a controller 50c, the property of vibration generated during the position control can be reduced by adjusting a viscosity friction coefficient.

[21] The piston rod 31 is guided to perform a linear motion by the sliding bearing 32 installed on the sliding bearing support bracket 34. The friction force generated during the movement of the piston rod 31 is only a friction force generated from a contact surface between the sliding bearing 32 and the piston rod 31 so that a very small friction force is applied.

[22] Consequently, in a low friction pneumatic cylinder according to the present invention, since the piston rod is 31 advanced by the pressure of air generated inside the elastic rubber 27 by injecting air into or exhausting air from the chamber formed by the elastic rubber 27 and the fixing bracket 25 and a driving force generated by an inner surface area of the elastic rubber 27, and the piston rod 31 is returned by a restoring force of the spring 29, the effect of the friction force can be ignored. However, since a position control property may be dependent on the properties of the elastic rubber 27 and the spring 29, the selection of these elements is important. Also, to improve accuracy in the position determination, the accuracy varies according to the resolution of the displacement sensor 21a and the controller 50c provided in a control unit 50 (please refer to FlG. 3), the controller 50c needs to be carefully designed.

[23] FlG. 3 shows a system for controlling the position of the pneumatic cylinder of

FlG. 2. The system is configured to control the position of the pneumatic cylinder using elastic rubber shown in FlG. 1. The system includes an air input valve module 40b for supplying compressed air through the air injection hole 25a so that the piston rod 31 can advance, an air output valve module 40a for exhausting the compressed air in the chamber defined by the elastic rubber 27 and the fixing bracket 25 through the air injection hole 25a so that the piston rod 31 can retreats, the controller 50c which receives the signal of the displacement sensor 21a through an input port 50a, compares the information with a target value, generates a positional error, and calculates opening and closing time of a solenoid valve (not shown) using the generated positional error, and a valve driving unit 46 for controlling the control unit 50 that outputs the control signal of the controller 50c through an output port 50b and the air input and output valve modules 40a and 40b by receiving the control signal of the control unit 50.

[24] FlG. 4 is a view showing the flow of a signal in the system of FlG. 3. Referring to

FlG. 4, a method of controlling the position of the pneumatic cylinder using elastic rubber configured as above is described. [25] First, the displacement sensor 21a installed on the pneumatic cylinder 20 measures the displacement of the piston rod 31.

[26] Second, the signal obtained from the measurement of the displacement of the piston rod 31 passes through a signal processor 51 and is input to an A/D converter (not shown) through the input port 50a. The analog signal of the displacement sensor 21a is converted into a digital signal by the A/D converter and then into positional information by a measurement portion (not shown). The control unit 50 using a microprocessor compares a target position given by a user setting with the output of the measurement portion obtained by converting the signal of the displacement sensor into the positional information, determines whether a target value has reached, and generates a positional error with respect to the target value.

[27] Third, by determining whether the generated positional error has either a positive value or a negative value, solenoid valves 403 and 404 of the air input valve module 40b and solenoid valves 401 and 402 of the air output valve module 40a are operated.

[28] When the positional error having a positive value is greater than an arbitrary set value, the solenoid valve 403 is operated. When the positional error having a positive value is less than the set value, the solenoid valve 404 is operated to supply a small amount of air flow to the pneumatic cylinder 20. The compressed air supplied to the solenoid valves 403 and 404 is controlled using speed control valves 43 and 44. The speed control valve 43 is adjusted to have a sectional size greater than that the speed control valve 44. Thus, when the positional error is greater than the set valve, the compressed air is supplied to the pneumatic cylinder 20 through the speed control valve 43. When the positional error is less than the set valve, the compressed air is supplied to the pneumatic cylinder 20 through the speed control valve 44 having a decreased sectional size after passing the solenoid valve 404 so that a fine movement is possible.

[29] When the positional error having a negative value is less than to the set value, since an actual displacement has already far passed the target position, the compressed air in the pneumatic cylinder 20 passes the solenoid valve 401 through the speed control valve 41 having an increased sectional size to the outside air. When the positional error is greater than the set value, since an actual displacement is close to the target position, to make a fine movement, the compressed air in the pneumatic cylinder 20 passes the solenoid valve 402 through the speed control valve 42 having a decreased sectional size to the outside air. Therefore, precise position determination is realized.

[30] Fourth, when the positional error is generated, a control input in which the operation time of the solenoid valve is used as the control signal is calculated using the positional error. The digital controller 50c is designed by writing a program in the control unit 50. The operation time of the solenoid valve calculated by the control portion is transferred to the valve driving unit 46 via the output port 50b. The valve driving unit 46 transmits an air input or output signal to the respective solenoid valves according to the air input or output determined by the sign of the positional error to control the solenoid valves.

[31] When the positional error is positive, compressed air 45 supplied by a compressor

(not shown) is input to a port P of each of the solenoid valves 403 and 404 and output to the pneumatic cylinder 20 through a port A. Thus, the elastic rubber 27 expands and the piston rod 31 advances. When the positional error is negative, the compressed air existing in the pneumatic cylinder 20 is input to the port P of each of the solenoid valves 401 and 402 and output to the air through the port A. Thus, the elastic rubber 27 contracts and the piston rod 31retreates by the restoring force of the spring 29.

[32] While this invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

[33] As described above, according to the present invention, in an apparatus for processing or checking a thin, light plate, when the plate is centered or aligned by directly manipulating the plate, by manipulating the plate with a small force, precise position determination is possible without causing deformation by applying an excessive force to the plate.

[34] Also, when the absolute value of the positional error is great, by adjusting the sectional size of the speed control valve to be large, a large amount of air is supplied to the solenoid valve so that the target value is quickly approached. When the absolute value of the positional error is small, by adjusting the sectional size of the speed control valve to be small, a small amount of air is supplied to the solenoid valve so that precise position determination is made possible.

[35] Furthermore, since the pneumatic cylinder is configured such that the piston rod is capable of advancing and retreating using the expansion and contraction of the elastic rubber, sliding friction is minimized and the elastic rubber changes according to the change in the amount of air supplied into the chamber of the pneumatic cylinder. Accordingly, a precise air flow amount control technique is required, which is implemented using the speed control valves having differently adjusted sectional sizes.

Claims

[1] L A pneumatic cylinder using elastic rubber used for an alignment apparatus or a centering apparatus of a board, the pneumatic cylinder comprising: a cylinder cover protecting a cylinder head; a fixing bracket having an air injection hole to inject air; elastic rubber having a hemispheric shape, fixed in the cylinder cover with respect to the air injection hole of the fixing bracket, and expanding and contracting according to a change in the amount of compressed air that is supplied and exhausted through the air injection hole; a piston rod penetrating the cylinder cover and advancing and retreating according to a change in the amount of the expansion and contraction of the elastic rubber; a spring installed at the piston rod and allowing the piston rod to advance and retreat according to the expansion and contraction of the elastic rubber; a sliding bearing guiding a linear motion of the piston rod; a sliding bearing support bracket supporting the sliding bearing; a displacement sensor measuring the displacement of the piston rod; a sensor dog transferring the displacement of the piston rod to the displacement sensor; and a fixed plate on which the fixing bracket, the cylinder cover, and the sliding bearing support bracket are fixedly installed.

2. The pneumatic cylinder of claim 1, further comprising a fluid damper which increases a viscosity friction coefficient in the movement of the piston rod.

3. The pneumatic cylinder of claim 2, wherein a lower end portion of the sensor dog is sunk under the fluid damper.

4. A system of controlling the position of the pneumatic cylinder using elastic rubber configured according to claim 1, the system comprising: an air input valve module supplying compressed air through the air injection hole to allow the piston rod to advance; an air output valve module exhausting the compressed air in a chamber defined by the elastic rubber and the fixing bracket to the outside through the air injection hole to allow the piston rod to retreat; a control unit having a controller which receives a signal of the displacement sensor through an input port, compares information obtained from the signal with a target value to generate a positional error, and calculates the opening and closing time of a solenoid valve using a value of the positional error, and outputting a control signal of the controller through an output port; and a valve driving unit receiving the control signal of the control unit and controlling the air input and output valve modules.

5. The system of claim 4, wherein the air input valve module comprises: a pair of solenoid valves connected to the air injection hole and supplying the compressed air; and a pair of speed control valves having different sectional sizes to adjust the flow amount of the solenoid valves, and the air output valve module comprises: a pair of solenoid valves exhausting the compressed air existing in the pneumatic cylinder; and a pair of speed control valves having different sectional sizes to adjust the flow amount of the solenoid valves.

6. A method of controlling the position of the pneumatic cylinder using elastic rubber configured according to claim 1, the method comprising:

(a) measuring the displacement of the piston rod which changes according to the change in the amount of the compressed air supplied to the elastic rubber, using the displacement sensor contacting the sensor dog, inputting the measured displacement to an input port included in a control unit via a signal processor, and converting the measured displacement into a digital valve by an A/D convert;

(b) generating a positional error by comparing the converted digital valve passing a measurement portion with a target valve set by a user in advance;

(c) determining whether the generated positional error has a negative value or a positive value to operate a solenoid valve of an air output valve module and a solenoid valve of an air input valve module; and

(d) when the positional error is generated, calculating operation time of the solenoid valve using the positional error, transferring the calculated operation time of the solenoid valve to the valve driving unit via an output port, and controlling the solenoid valve by transmitting an air input signal or an air output signal to each of the solenoid valves according to the air input or output determined by the sign of the positional error at the valve driving unit.

7. The method of claim 6, wherein the step (c) sub-comprises:

(cl) when a positional error having a negative value is less than to an arbitrary set value, the compressed air in the pneumatic cylinder passes the solenoid valve through a first speed control valve having an increased sectional size to the outside air, and when the positional error having a negative value is greater than the set value, since an actual displacement is close to a target position, to make a fine movement, the compressed air in the pneumatic cylinder passes the solenoid valve through a second speed control valve having a decreased sectional size to the outside air; and

(c2) when a positional error having a positive value is greater than the set value, the compressed air adjusted by a third speed control valve having an increased sectional size operates the solenoid valve and is supplied to the pneumatic cylinder, and when the positional error having a positive value is less than the set value, the compressed air adjusted by a fourth speed control valve having a decreased sectional size operates the solenoid valve and is supplied to the pneumatic cylinder.