JP2892451B2 - Electric-pneumatic servo actuator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to an electro-pneumatic servo actuator capable of sliding and positioning a drive rod with a large force by air based on an electric signal.

[Prior art]

Conventionally, liquid (oil) or air has been widely used as an operating medium of an actuator for performing an operation based on an electric signal. An actuator that uses air as a working medium can use a pneumatic line that is usually installed in a factory as a source of compressed air for the actuator, does not require a separate drive source, does not use oil, and is clean. On the other hand, there is a problem that control of speed adjustment, stop of the intermediate position of the stroke, and the like is extremely difficult. Conventionally disclosed electric-pneumatic control technologies include PT
There are P method (point to point method) and servo method. In the PTP method, for example, as shown in FIG. 4, a drive rod connected to a load is moved to stop at a fixed point, and only positioning can be performed and tracking operation cannot be performed. Specifically, there are a method using a mechanical stopper and a method using both a position detector and a brake. On the other hand, the servo method is a method in which an electropneumatic control valve is used as shown in FIGS. 5 and 6 (A) to form an electric feedback system using a position detector. This method can perform a follow-up operation in addition to arbitrary positioning, but has a problem that high response and accuracy cannot be maintained due to an operation delay of the electropneumatic control valve. To cope with such a problem, Japanese Patent Application Laid-Open No. 62-270801 proposes a servo cylinder as shown in FIG. In brief, when the drive rod 16 is projected in the direction indicated by the arrow X in this servo cylinder, first, as shown in FIG. 7A, an electric motor (not shown) is used.
As a result, the screw shaft 22 is rotated to move the nut block 21 against the compression spring 24 in the direction of the arrow in the figure. Since the movement of the poppet valve 20 in the left direction in the figure is restricted by the stopper 27, the compressed air flowing from the port 17 reaches the airtight chamber 45 through a passage shown by an arrow. As a result, the piston 15 integrated with the rod 16 is pushed to the left in the drawing, and the nut block 21 moves to a position neutral with respect to the left and right poppet valves 19, 20 and stops there. On the other hand, when retracting the rod 16, as shown in FIG. 7B, the screw shaft 22 is reversed to move the nut block 21 in the direction of the arrow in the figure. as a result,
The air in the airtight chamber 45 is discharged to the atmosphere through a passage indicated by an arrow. As a result, the piston 15 moves to the right side in the drawing, and also stops at a position where the nut block 21 is neutral with respect to the poppet valves 19 and 20. As shown in FIG. 6 (B), this servo actuator has a relatively good response and a higher control accuracy than the conventional one because the position control system is mechanically constructed. .

[Problems to be solved by the invention]

However, the servo actuator disclosed in Japanese Patent Application Laid-Open No. 62-270801 requires a pair of poppet valves 19 and 20 having a complicated elbow passage in addition to the screw shaft 22 and the nut block 21. Stoppers 26, 2
7. Since elements such as the compression springs 24 and 25 are also essential, there is a problem that the apparatus is complicated and the cost is likely to increase. In addition, since the passage of the air is switched using a poppet valve (a valve in which the valve element moves in a direction perpendicular to the valve seat), the motor supports the poppet in addition to the inertial force of the poppet valve. A force against the spring force and a force against the external force due to the air pressure applied to the pressure receiving surface of the poppet valve must be generated.
There was also a problem that stability was deteriorated. SUMMARY OF THE INVENTION The present invention has been made in view of such a conventional problem, and realizes a low cost by further simplifying a servo configuration, and has a good response and a high stability at the time of positioning. It is an object to provide a pneumatic servo actuator.

[Means for Solving the Problems]

The present invention provides a piston in which a drive rod connected to a load is connected or integrally extended in a cylinder body in an airtight and slidable manner, and a sliding direction of the piston is provided inside the piston. A spool slidably disposed in the same direction and having a groove formed on the outer periphery, an electric motor for sliding and positioning the spool in the piston via a screw-nut screwing mechanism, and the spool A sleeve arranged integrally with the piston on the outer periphery thereof,
A compressed air source, two hermetic chambers formed by a piston in the cylinder body, and an air passage formed between four members of the atmosphere, wherein the air passage is formed in the sleeve. At least one of the air passages
The opening cross-sectional area of the air passage with respect to the groove of the sleeve is formed in a shape such that it differs in the sliding direction of the spool, and the flow direction of air in the air passage is changed by the groove formed on the outer periphery of the spool. The piston is slid / positioned in accordance with the sliding / positioning of the spool by the electric motor, and a specific groove of the spool is cut off in accordance with the position of the spool. The above object has been achieved by adopting a configuration in which the air passage having a different area is connected to a side having a specific opening cross-sectional area of an air passage.

[Action]

In the present invention, when positioning the piston to which the drive rod connected to the load is connected or integrated, first, the spool is slid and positioned in the piston via a screw-nut screwing mechanism, and this positioning is performed. Accordingly, the axial position of the groove formed on the outer periphery of the spool with respect to the piston is deviated, and the air passage formed between the compressed air source, the two airtight chambers in the cylinder body, and the atmosphere is switched. Is being done. For this reason, the number of parts is small, and the force generated by the motor is only the inertial force of the spool, so that a system having high responsiveness and high stability can be constructed.
Further, in the present invention, a sleeve is arranged continuously and integrally with the piston on the outer periphery of the spool, and at least one of the air passages arranged in the sleeve is provided with an opening cross-sectional area with respect to the groove for sliding the spool. Since the spool is formed differently in the moving direction, the flow rate of the air passing through the air passage can be maintained constant regardless of the position of the spool (for example, when the spool advances or retreats). Therefore, the piston response speed can always be kept constant.

【Example】

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. A piston 104 is hermetically and slidably incorporated in a cylindrical cylinder body 102. A sleeve 106 is integrally fixed to the piston 104 coaxially, and a drive rod 108 connected to a load is integrally connected to the sleeve 106. This drive rod 108 is connected to the cylinder body 102
And is slidably supported by a bearing 102B. Reference numeral 110 is a rod seal. Inside the piston 104, specifically, inside the sleeve 106 integrated therewith, a spool 112 is incorporated so as to be slidable in the same direction as the piston 104 slides. A detent key 114 is attached to the spool 112. Further, a stopper 116 is provided to limit axial displacement of the spool 112 with respect to the piston 104. However, this stopper 116 is not essential for the present invention itself. A nut 118 is fixed to the spool 112, and a ball screw shaft 120 is screwed thereto. The shaft end of the ball screw shaft 120 is rotatably attached to a cover 132 by a bearing 122, and is connected to a stepping motor 128 via a coupling. A keyway is provided on the stepping motor 128 side of the piston 104.
130 is cut off, and engagement with a key 134 fixed to the cover 132 guides sliding of the piston 104 and prevents rotation thereof. Inside the cover 132, the piston 104, and the sleeve 106, passages 151 to 158 through which air is provided are provided.
6. The first and second hermetic chambers 138 and 140 formed by the piston 104 in the cylinder body 102 and the atmosphere 142 are connected to each other. These passages 151 to 158 are formed by grooves 112A and 112B formed on the outer periphery of the spool 112.
The direction of air flow through each of the passages 151 to 158 is switched depending on the position of the spool 112. Further, as shown in detail in FIGS. 2 and 3, the valve portion constituted by the spool 112 and the sleeve 106 includes a first airtight chamber (constant pressure chamber) 138 to a second airtight chamber (control pressure chamber) 140. In order to make the flow rate of air flowing into the airtight chamber equal to the flow rate of air flowing out of the second hermetic chamber 140 to the atmosphere, that is, the speed when the drive rod 108 moves backward and the speed when the drive rod 108 moves forward, the passage 155 of the sleeve 106 is formed. The lengths l ₁ and l ₂ in the circumferential direction are different from each other in the front-rear direction (axial direction). More specifically, the air pressure Ps of the compressed air source 136
Is about 7 kgf / cm ² · G, and the chamber pressure in the second airtight chamber 140 is about 1/2 Ps =
Assuming that 3.5 Kgf / cm ² · G, when the drive rod 108 retreats, air of 7 Kgf / cm ² · G → 3.5 Kgf / cm ² · G flows through the passage 155, while the drive rod 108 moves forward Sometimes, air of 3.5 kg / cm ² · G → 0 kgf / cm ² · G (atmosphere) flows through the passage 155. Therefore, if the cross-sectional area of the passage 155 is the same in the axial direction, the latter will flow only 1 / 1.7 of the air, and the response will be inferior. For this reason, in this embodiment,
The circumferential length l ₁ of a portion X ₁ used when opening cross-sectional area of the driving rod 108 with respect to the groove 112A or 112B of the spool 112 of the passage 155 in 6 moves forward, the portion X used when retracted varied by about 1.7 times the _second circumferential length l _2, is obtained so as to ensure equal response speed of advancement and retraction of the drive rod 108. Next, the operation of this embodiment will be described. When the stepping motor 128 rotates clockwise as viewed from the shaft side, the ball screw shaft 120 also rotates integrally. Nut 1 screwed into this ball screw shaft 120
18 is fixed to a spool 112 and the spool 1
The key 12 is detented with respect to the piston 104 by a key 114, and the piston 104 is detented with respect to the cover 132 by a key 134. Therefore, the nut 118 eventually starts to advance by the rotation of the ball screw shaft 120. In addition, the spool 112 advances integrally with the advance of the nut 118. As a result, the grooves 112A, 112 of the spool 112
A deviation occurs between B and the passages 154 to 156 of the sleeve 106, resulting in the state shown by the broken line in FIG. For this reason passage 15
1. Since the first airtight chamber 138, the passages 152 and 153, and the groove 112A of the spool 112 form a closed space, the inflow of air from the compressed air source 136 is prevented. On the other hand, the air in the second airtight chamber 140 passes through the passages 154 and 155 and the groove 112.
B, released to atmosphere via passages 156, 157, 158. Accordingly, the air pressure in the second hermetic chamber 140 decreases, and the piston 104
The force balance in the front-rear direction is lost, and the piston 104 moves forward together with the sleeve 106 and the drive rod 108. However, since the spool 112 does not move with them, the passage between the grooves 112A and 112B of the spool 112 and the sleeve 106 will soon be established.
When the deviation from 154 to 156 becomes 0 again, the outflow of the air in the first airtight chamber stops, and the movement of the piston 104 also stops. As a result, when the ball screw shaft 120 is eventually rotated by the electric motor 128 and the nut 118 is positioned at an arbitrary position, the drive rod 108 is slid and positioned corresponding to the axial position thus positioned. . Conversely, the electric motor 128 rotates counterclockwise and the spool 1
When 12 retreats, a deviation occurs between the groove portions 112A and 112B of the spool 112 and the passages 154 to 156 of the sleeve 106 on the opposite side from that at the time of forward movement, and the release of the air in the second airtight chamber 140 to the atmosphere is prevented. And the first airtight chamber 1 communicated with the compressed air source 138.
The air of 38 flows into the second hermetic chamber 140 via the passages 152 and 153, the groove 112A, and the passages 155 and 154. Thus, the second hermetic chamber 1
The air pressure at 40 rises, the force balance in the front-rear direction of the piston 104 is lost, and the piston 104 retreats. Due to this retreat, the passages 15 between the groove portions 112A and 112B of the spool 112 and the sleeve 106 are formed.
When the deviation from 4 to 156 becomes zero again, further movement of air is stopped, and the retreat of the piston 104 is completed. In the above two operations, in this embodiment, the passage 155
The difference in the circumferential lengths l ₁ and l ₂ of
Passage 154 between groove 112A, 112B of spool 112 and sleeve 106
The ratio of the flow rate to the deviation from ~ 156 is the same,
For this reason, the responsiveness is equal between the forward movement and the backward movement. According to this embodiment, as shown in FIG. 6 (B), since the position control system is mechanically configured and the flow path is switched by a spool valve, an extra air pressure is applied to the valve itself. The switching can be performed very stably since no external force or holding force by the spring is received. Therefore, as a result, the response of the position control system of the stepping motor can be maintained high, and the positioning accuracy can be improved.

【The invention's effect】

As described above, according to the present invention, since the spool valve is used as a main element constituting the position control system, the number of parts is small, the cost can be reduced, and the driving force of the motor can be greatly increased. The excellent effect that the response can be further improved because the reduction can be achieved, and the positioning at a specific position can be stably performed can be obtained.

[Brief description of the drawings]

1 is a longitudinal sectional view of an electric-pneumatic servo actuator to which the present invention is applied, FIG. 2 is a partial perspective view of a portion II in FIG. 1, and FIG. 3 is a partial sectional view of a sleeve along the line III-III. Fig. 4 is a block diagram of a conventional PTP type electro-pneumatic servo actuator, Fig. 5 is a block diagram of a conventional servo system, and Figs. 6 (A) and 6 (B) are a conventional servo system and the above embodiment. FIG. 7A and FIG. 7B are longitudinal sectional views of a conventional electric-pneumatic servo cylinder. 102 ... Cylinder body, 104 ... Piston, 106 ... Sleeve, 108 ... Drive rod, 112 ... Spool valve, 112A, 112B ... Groove, 118 ... Nut, 120 ... Ball screw shaft, 128 ... Stepping motor, 136: compressed air source, 138: first hermetic chamber (constant pressure chamber), 140: second hermetic chamber (control pressure chamber), 151 to 158: passage.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F15B 9/09

Claims (1)

(57) [Claims] 1. A piston, which is airtightly and slidably disposed in a cylinder body and has a drive rod connected to or integrally extended with a load, and a sliding direction of the piston inside the piston. A spool slidably disposed in the same direction as the above, and having a groove formed on the outer periphery; an electric motor that slides and positions the spool within the piston via a screw-nut screwing mechanism; A sleeve arranged integrally with the piston on the outer periphery of the spool, a compressed air source, two hermetic chambers formed by the piston in the cylinder body, and an atmosphere; Wherein at least one of the air passages formed in the sleeve has an opening cross-sectional area of the spool corresponding to the groove of the sleeve. The air flow direction in the air passage is switched depending on the position of the spool by a groove formed on the outer periphery of the spool, and the sliding of the spool by the electric motor is performed. In addition to sliding and positioning the piston in accordance with movement and positioning, a specific groove of the spool is connected to a side of a specific opening cross-sectional area of the air passage having a different opening cross-sectional area according to a position of the spool. An electric-pneumatic servo actuator characterized by having a configuration as described above.