WO1999000603A1

WO1999000603A1 - Rotary actuator

Info

Publication number: WO1999000603A1
Application number: PCT/KR1998/000174
Authority: WO
Inventors: Yong Woo Lee
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-06-30
Filing date: 1998-06-23
Publication date: 1999-01-07
Anticipated expiration: 1999-12-30
Also published as: KR19990004838A

Abstract

A rotary actuator for generating opposite directional torque is disclosed. The actuator has a hydraulic cylinder (10) with two chambers (12, 13) being divided by a piston (30). Two brackets (20, 20a) close both ends of the cylinder (10) and individually have oil inlet and outlet ports (22, 22a; 23, 23a) allowing pressurized oil to be selectively introduced into or discharged from each of the chambers (12, 13). A rotor shaft (40), with a spiral part, movably passes through the center of the piston (30) with both ends of the shaft (40) being rotatably held by the two brackets (20, 20a), thus being rotatable in either direction in accordance with a linear movement of the piston (30) and generating opposite directional torque. The spiral part of the shaft has a polygonal cross section and is twisted with a plurality of helixes (41). The opposite directional torque of the actuator is transmitted to a machine through an output shaft, which is coupled to the rotor shaft by a coupling.

Description

ROTARY ACTUATOR

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates, in general, to rotary actuators used for converting a linear motion into a rotating motion, thus generating opposite directional torque with a limited rpm (revolutions per minute) and, more particularly, to a rotary actuator with a pneumatic or hydraulic reciprocating piston selectively rotating a shaft in either direction, thus generating opposite directional torque stably and precisely.

Description of the Prior Art As well known to those skilled in the art, a rotary actuator is typically comprised of a rotor shaft, which is rotatably placed in a cylinder and is connected to an output shaft thus outputting torque through the output shaft. A sprin -biased vane is radially set on the rotor shaft, with the tip of the vane being brought into close contact with the internal surface of the cylinder and being slidable on the internal surface thereby allowing the rotor shaft to be rotated in the cylinder.

The cylinder has two ports, through each of which pressurized air or oil is selectively introduced into or discharged from the cylinder in accordance with the pumping operation of a pump. That is, each of the two ports in a rotary actuator selectively acts as an inlet or outlet port of the cylinder, with the other port being used as an outlet or inlet port.

Therefore, when the two ports are alternately used for introducing the pressurized air or oil into the cylinder, the rotor shaft, with the vane, rotates in opposite directions in the cylinder and outputs opposite directional torque through the output shaft. However, the above rotary actuator is problematic in that the rotor shaft is rotated by the pressurized air or oil acting on the vane, thus failing to generate large torque. In order to prevent leakage of pressure through the gap between the vane and the internal surface of the cylinder, it is necessary to provide a packing member in the gap, thus complicating the construction of the actuator.

Another problem experienced in the typical rotary actuator is that when the rotating direction of the rotor shaft is changed or the rotor shaft is stopped, the rotor shaft is overloaded thereby failing to generate stable torque.

In the prior art, such torque may be generated by a reduction motor in place of the rotary actuator.

In a typical reduction motor, such torque is generated by the magnetic hne of force formed by current flowing through the coil of a stator. Therefore, such a reduction motor has the following problems when it is required to generate large torque.

In order to allow a reduction motor to generate large torque, the reduction motor has to be large-sized and provided with a reduction mechanism such as reduction gears. Another problem of the typical reduction motor resides in that a large-sized reduction motor is not suitable for generating extremely limited torque.

In an effort to overcome the above problems, a rack/pinion -type rotary actuator, which is capable of converting a linear motion into a rotating motion thus generating opposite directional torque, is proposed.

The rack/pinion- type rotary actuator is comprised of a rack, which is placed in a cylinder so as to linearly reciprocate within a limited distance using separate power. A pinion, with a rotor shaft, engages with the rack thus being rotatable in either direction by a linear movement of the rack. The rotor shaft passes into the outside of the cylinder and is connected to an output shaft at the outside of the cylinder.

In the operation of the rack/pinion -type rotary actuator, the pinion is rotated in either direction in accordance with a linear movement of the rack, thus generating opposite directional torque which is output from the cylinder through the output shaft.

However, the rack/pinion -type rotary actuator is problematic in that it has a complex gear transmission comprised of the rack and pinion for converting a linear motion into a rotating motion. The complex gear transmission reduces the productivity of the actuator and is limited in that its requires a large area for installing the actuator. The gear transmission also fails to accomplish stable and precise power transmission.

In addition, when a linear motion of the rack is converted into a rotating motion of the pinion, the moving direction of the rack is perpendicular to the rotating axis of the pinion. The rotor shaft of the pinion thus maintains its center of gravity eccentrically so that the shaft causes eccentric frictional abrasion of its contact parts and the reduction of its torque.

Another problem experienced in the rack/pinion -type rotary actuator is that the actuator may form an operational error when it is stopped. That is, in order to stop the actuator, the rack is primarily stopped with both the pinion and the rotor shaft retaining their rotating motions. Therefore, the rotating force (reaction force) of the pinion and rotor shaft is fed back to the rack at the initial stage of stopping the actuator, thus preventing the actuator from being stably and precisely stopped.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art. An object of the present invention is to provide a rotary actuator which is provided with a pneumatic or hydraulic reciprocating piston ⁽hereinbelow, referred to simply as "hydraulic piston") selectively rotating a spiral shaft in either direction thus generating opposite directional torque stably and precisely.

Another object of the present invention is to provide a rotary actuator which effectively generates large torque and is stopped with precision by stopping the introduction of pressurized oil into a cylinder. A further object of the present invention is to provide a rotary actuator which is positioned with high precision thus being effectively used for various industrial applications requiring opposite directional torque.

In order to accomplish the above objects, the present invention provides a rotary actuator for generating opposite directional torque, comprising: a cylinder; a reciprocating piston movably received in the cylinder while dividing the interior of the cylinder into two variable chambers; two brackets attached to both ends of the cylinder and tightened by a plurality of fixing bolts thereby closing the ends o the cylinder, each of the brackets having fluid inlet and outlet ports connected to a pressurized fluid circuit thus allowing pressurized fluid to be selectively introduced into or discharged from each of the chambers; a rotor shaft having a spiral part and axially extending in the cylinder while movably passing through the center of the piston with both ends of the shaft being rotatably held by the two brackets, thus being rotatable in either direction in accordance with a linear movement of the piston and generating opposite directional torque, the spiral part of the shaft having a polygonal cross-section and being twisted with a plurality of helixes; and an output shaft coupled to one end of the rotor shaft by a coupling and adapted for transmitting the opposite directional torque to a machine. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a perspective view showing the construction of a rotary actuator in accordance with the preferred embodiment of the present invention;

Fig. 2 is an exploded perspective view of the rotary actuator of this invention;

Fig. 3 is a sectional view of the rotary actuator of this invention; Fig. 4 is a sectional view of the rotary actuator of this invention taken along the line A-A of Fig. 3;

Fig. 5 is a front view showing the configuration of a rotor shaft of the rotary actuator according to this invention; and

Fig. 6 is a sectional view of the rotary actuator of this invention taken along the line B-B of Fig. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figs. 1 to 6 show the construction of a rotary actuator in accordance with the preferred embodiment of this invention. In the drawings, the rotary actuator is designated by the reference numeral 100. For ease of description, the end of the actuator 100 on the left-hand side of the drawings will be referred to as left end of the actuator 100 and the opposite end on the right-hand side of the drawings will be referred to as the right end.

The actuator 100 is comprised of a cylinder 10, with two rectangular plate brackets 20 and 20a being tightly attached to both ends of the cylinder 10 and holding the cylinder 10. A piston 30 is movably received in the cylinder 10 in a way such that the external surface of the piston 30 is brought into slidable contact with the internal surface of the cylinder 10. The piston 30 is linearly movable in either direction in the cylinder 10 by pressurized oil thus being called a hydraulic piston. A rotor shaft 40, having a spiral part, axially extends in the central axis of the cylinder 10. The shaft 40 also passes through and engages with the center of the piston 30 and so the shaft 40 is rotatable in either direction in accordance with a linear movement of the piston 30.

The cylinder 10 has a hollow cylindrical body, with both ends being tightly closed by the two brackets 20 and 20a. The two brackets 20 and 20a are tightened by a plurality of longitudinal fixing bolts 11, which axially extend at the outside of the cylinder 10 and are individually tightened by a nut at the outside of the left bracket 20. The piston 30 divides the interior of the cylinder 10 into two pressure chambers 12 and 13. Each of the chambers 12 and 13 is selectively used as a pressure inlet or outlet chamber, thus allowing the piston 30 to linearly move in either direction in accordance with which chamber is the inlet chamber.

Each of the brackets 20 and 20a is shaped into a rectangular plate configuration. Provided on the inside center surface of each bracket 20, 20a is a circular fitting boss 21, which is fitted into each end of the cylinder 10 thus stably and precisely centering each bracket 20, 20a to the cylinder 10.

Each bracket 20, 20a has a predetermined thickness and has two ports: an oil inlet port 22, 22a and an oil outlet port 23, 23a which extend from the fitting boss 21 to two side walls of each bracket respectively thus communicating with an associated chamber 12, 13 of the cylinder 10. Therefore, it is possible to introduce or discharge pressurized oil into or from each chamber 12, 13. Of course, an oil pipe (not shown) extends from each port 22, 22a, 23, 23a of the actuator 100 to an oil pump of a hydraulic circuit.

A plurality of guide rods 24 axially extend inside the cylinder 10 with both ends of each guide rod 24 being held by the bosses 21 of the two brackets 20, 20a. Each of the guide rods 24 movably passes through the piston 30 thus guiding a linear movement of the piston 30 in the cylinder 10 while preventing the piston 30 from unexpectedly rotating in the cylinder 10.

The guide rods 24 are also used as an assembling means for finally assembling the elements of the actuator 100 into a single body. In the preferred embodiment shown in the drawings, three guide rods 24 are positioned in the cylinder 10 at the angular points of a regular triangle surrounding the rotor shaft 40. However, it should be understood that the number and position of the guide rods 24 is not limited to the preferred embodiment. The piston 30 is shaped into a circular disc with a predetermined thickness. The outside diameter of the piston 30 is predetermined to allow the piston 30 to be brought into slidable and close contact with the inside surface of the cylinder 10. A center opening 31 is formed on the center of the piston 30 and receives the rotor shaft 40.

In the preferred embodiment, the spiral part of the rotor shaft 40 has a hexagonal cross-section and so the center opening 31 of the piston 30 is shaped into a hexagonal opening corresponding to the cross- section of the shaft 40. A packing 32 is fitted over the piston 30, while another packing 33 is fitted in the center opening 31. The two packings 32 and 33 prevent the two chambers 12 and 13 of the cylinder 10 from communicating with each other.

As best seen in Fig. 5, the rotor shaft 40 has a hexagonal cross-section at its spiral part which is twisted with six helixes 41. The left end of the rotor shaft 40 passes through the center opening 25 of the left bracket 20 prior to being coupled to an output shaft 50 through a coupling 51 at the outside of the bracket 20. In the preferred embodiment, the spiral part of the rotor shaft

40 has a hexagonal cross-section as described above. However, it should be understood that the spiral part may have another polygonal cross- section with four or more straight sides in place of the hexagonal cross-section.

In accordance with practical experiments, it is most preferable to give each helix 41 of the rotor shaft 40 a spiral angle θ of 20 - 30 ^" . The length of each helix 41 is predetermined by the maximum rotating angle of the shaft 40. The rotor shaft 40, with a predetermined length, axially extends in the central axis of the cylinder 10, with the left end of the shaft 40 being rotatably supported by a bearing 42a in the boss 21 of the right bracket 20a. Meanwhile, the right end of the rotor shaft 40 has a step which is rotatably held by a bearing 42 in the boss 21 of the left bracket 20.

Since the rotor shaft 40 movably passes through the center opening 31 of the piston 30, with both ends of the shaft 40 being rotatably held by the two bearings 42 and 42a in the brackets 20 and 20a, the shaft 40 is smoothly rotated in accordance with a linear movement of the hydraulic piston 30.

The operational effect of the above actuator 100 will be described hereinbelow.

When the elements of the actuator 100 are assembled into a single body as shown in Figs. 1 and 3, the left end of the shaft 40 passes through the left bracket 20 thus being exposed into the outside of the bracket 20. The exposed left end of the shaft 40 is coupled to the output shaft 50 through the coupling 51.

In the above actuator 100, the output shaft 50 transmits the opposite directional torque of the actuator 100 to a machine requiring such torque. For example, the output shaft 50 is connected to the rotor shaft of a turntable, thus rotating the turntable in opposite directions at predetermined rotating angles. When an oil pump of a hydraulic circuit including the actuator

100 is started, the pump feeds pressurized oil into either chamber 12,

13 of the cylinder 10 through an associated inlet port 22, 22a. The pressurized oil thus acts on the left or right side of the piston 30 in the cylinder 10 and pushes the piston 30 to the right or to the left.

In order to generate forward torque, pressurized oil is introduced into the left chamber 12 through the oil inlet port 22 of the left bracket 20 and the pressurized oil acts on the left side of the piston 30 thus pushing the piston 30 to the right. Therefore, the piston 30 moves from the left position indicated by the solid line of

Fig. 3 to the right position indicated by the phantom line. In this case, oil of the right chamber 13 is discharged from the chamber 13 through the oil outlet 23a of the right bracket 22a and is returned to the oil pump. The guide rods 24 movably pass through the piston 30 and smoothly guide a linear movement of the piston 30 in the cylinder 10 while preventing the piston 30 from unexpectedly rotating in the cylinder 10. Therefore, the rightward movement of the piston 30 causes the rotor shaft 40, passing through the center opening 31 of the piston 30, to be rotated in a forward direction.

The spiral part of the rotor shaft 40, which has a hexagonal cross-section and is twisted at a spiral angle, passes through the hexagonal center opening 31 of the piston 30. Therefore, when the piston 30 linearly moves to the right by pressurized oil in the cylinder 10 as described above, the rotor shaft 40 rotates in the forward direction and generates forward torque.

In the above actuator 100, the rotor shaft 40 is held by the bearings 42 and 42a of the brackets 20, 20a at both ends thereof thus being stably operated when it is rotated in the forward direction by the piston 30. The forward torque of the shaft 40 is transmitted to the output shaft 50 through the coupling 51 prior to being transmitted to a machine requiring the torque. In order to generate reversed torque, pressurized oil is introduced into the right chamber 13 through the oil inlet port 22a of the right bracket 20a and the pressurized oil acts on the right side of the piston 30 thus pushing the piston 30 to the left. In this case, oil of the left chamber 12 is discharged from the chamber 12 through the oil outlet 23 of the left bracket 22 and is returned to the oil pump. The piston 30 thus allows the rotor shaft 40 to be rotated in a reversed direction and to generate reversed torque.

When the actuator 100 is operated to generate opposite directional torque as described above, the rotating angle of the shaft 40 may be adjusted by controlUng the stroke of the piston 30. The stroke of the piston 30 is determined by the amount of pressurized oil fed into either chamber 12, 13. The rotor shaft 40 immediately stops rotating when the hydraulic circuit including the actuator 100 stops the feeding of pressurized oil into either chamber 12, 13.

That is, once the hydraulic circuit stops the feeding of pressurized oil into either chamber 12, 13, the oil pressures of the two chambers 12 and 13 are immediately balanced thereby precisely stopping the piston 30 without allowing the piston 30 to move in either direction.

Therefore, the rotary actuator 100 of this invention is free from a problem caused by a feedback of reaction force at the time when a typical rotary actuator is stopped.

The rotary actuator 100 of this invention thus precisely rotates the output shaft 50 at a predetermined rotating angle in either direction thus transmitting opposite directional torque to a machine requiring such torque.

As described above, the present invention provides a rotary actuator, which is provided with a pneumatic or hydraulic reciprocating piston rotating a rotor shaft at a predetermined angle in opposite directions thus generating opposite directional torque used by a machine. The rotor shaft, with a spiral part passing through the piston, is stably and precisely rotated at the center of the piston without having any eccentricity.

The rotary actuator of this invention uses pressurized air or oil, thus being effectively used with a machine requiring large torque. The rotor shaft of the actuator can be precisely stopped at any angular position and can be intermittently stopped at multiple points.

When the feeding of pressurized oil into either of two chambers of a cylinder is stopped, the oil pressures of the two chambers are immediately balanced thereby precisely stopping the piston without allowing the piston to move in either direction. The actuator of this invention is free from any operational error caused by reaction force in the event of a stopping of an operation, thereby removing the necessity of a brake device different from a typical rotary actuator. Therefore, the actuator of this invention improves its operational reliability.

The actuator of this invention has a simple construction, improving the operational efficiency of actuators and improving work efficiency in the production of such actuators. Another advantage of the actuator according to this invention resides in that it is possible to generate torque larger than that expected by a typical reduction motor with the same volume as the actuator.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

WHAT IS CLAIMED IS:

1. A rotary actuator for generating opposite directional torque, comprising: a cylinder; a reciprocating piston movably received in said cylinder while dividing the interior of the cylinder into two variable chambers; two brackets attached to both ends of said cylinder and tightened by a plurality of fixing bolts thereby closing the ends of the cylinder, each of said brackets having fluid inlet and outlet ports connected to a pressurized fluid circuit thus allowing pressurized fluid to be selectively introduced into or discharged from each of said chambers; a rotor shaft having a spiral part and axially extending in the cylinder while movably passing through the center of said piston with both ends of the shaft being rotatably held by the two brackets, thus being rotatable in either direction in accordance with a linear movement of said piston and generating opposite directional torque, said spiral part of the shaft having a polygonal cross-section and being twisted with a plurality of helixes; and an output shaft coupled to one end of said rotor shaft by a coupling and adapted for transmitting the opposite directional torque to a machine.

2. The rotary actuator according to claim 1, wherein each of said helixes of the rotor shaft has a spiral angle θ of 20 - 30 .

3. The rotary actuator according to claim 1, wherein the cross-section of said spiral part of the rotor shaft is a polygon with four or more straight sides.