WO2008012704A2 - Hydropneumatic regenerative actuator - Google Patents

Abstract

A hydropneumatic actuator applicable to linear actuations, comprising arrangements the purpose of which is to create internally and regeneratively a hydraulic pressure from the movement of the movable parts. These arrangements make it possible to slow the movement by finely adjusting its speed when this is required for the usage. The actuator comprises an annular pneumatic piston (Pp) provided with a movable tube (21) crimped in the internal bore of the piston, the pneumatic piston (Pp) being able to be moved in an external cylinder (Cy) under the effect of a pressure differential applied to the exterior by pneumatic connections (X1, X2). The actuator is further provided with a coaxial hydraulic piston (Ph) provided with a rod (10) sliding in a fixed coaxial lining (19, 20) separating the two pistons which remain attached to each other by a mechanical connection (1 1) between the end of the rod (10) of the hydraulic piston and the end of the movable tube (21). The actuator further includes electrical or pneumatic control valves, adjustable chokes, non-return valves, and an oil reservoir (15) kept under pressure by a spring (16) adjustable by a screw (1). The reservoir can be connected through valves, adjustable chokes and non-return valves to both sides of the hydraulic piston (Ph).

Description

 REGENERATIVE HYDROPNEUMATIC ACTUATOR.

The invention relates to a hydropneumatic actuator applicable to linear and rotary actuations, comprising provisions whose main purpose is to generate internally and regeneratively a hydraulic pressure from the movement of the moving parts, thereby at the same time slowing down the movement by finely adjusting its speed when required by use.

There are a large number of pneumatic and / or hydraulic actuators on the market. Some of them combine the advantages of the two types of fluid by bringing together in one and the same assembly one or more pneumatic circuits with one or more hydraulic circuits.

The principle of the pneumatic actuation has the advantage of obtaining high speed movements, this being however sensitive to the load that is to say the resistance to movement exerted by the use. In addition, the accuracy of the movement of the pneumatic actuators is affected by the compressibility of the fluid.

The principle of hydraulic actuation can counteract these two negative effects, so has the advantage of insensitivity to load variations, and accuracy; However, it has the disadvantage of a lower speed of the actuations, because of the viscosity of the hydraulic fluid used and the resulting pressure drops.

The known hydropneumatic combined linear actuators are most often made either in the form of one or more pneumatic actuators and one or more hydraulic actuators mounted in line in the same axis, therefore in the extension of one another, which involves a total length of the assembly reaching more than double the actual effective stroke, or in the form of actuators arranged parallel side by side, which substantially increases at least one of the transverse dimensions of the assembly, simultaneously increasing the weight of it. In both embodiments, precise arrangements must be made for the mechanical coupling of the actuators.

DE1001 1002 discloses a hydropneumatic actuator comprising a hydraulic pressure generating system; it has the disadvantage of using a flexible membrane and has a total length much greater than twice its stroke.

It is also known patent DE10026616 describing a compact hydropneumatic actuator, the hydraulic part of which allows a force amplification. However, the available stroke is very limited when compared to the total length, and the speed of travel is not finely adjustable by throttling of the hydraulic circuit.

For machining parts in the industry, where productivity demands require machine tools capable of performing multiple machining operations ("axes") at high speed on a workpiece without having to remove it from the chuck , the space reserved for the necessary multiple actuators is limited, requiring compact actuators of long stroke, combining speed and precision smoothly.

The purpose of the present patent application is to develop an actuator meeting these requirements, further allowing the adjustment of the working speed, not requiring external hydraulic pump, while remaining simple concept with a manufacturing cost competitive with existing actuators.

The solution to achieve this goal is contained in the features of independent claim number 1.

A hydropneumatic actuator corresponding to the state of the art comprises an external oil reservoir, a hydraulic pump, an electric motor, safety, non-return valves, directional valves, flow control valves, pneumatic cylinder and its connections, the hydraulic cylinder and its connections.

The actuator object of the present invention combines all the elements mentioned above in a single block. This actuator can be made to generate a linear motion, angular or rotary. It is operated by means of a compressed air connection of about 6 to 7 bars and also allows the use of hydraulic regeneration, taking advantage, when the actuator is moving, of the flow of water. oil from one side of the hydraulic piston to the other through an adjustable valve, which generates a hydraulic overpressure that can reach 300 or even 400 bar. The oil thus put under overpressure also results in a storage tank located in the rear compartment of the actuator. This high-pressure oil also exerts a counter-pressure effect opposing the main movement, a self-regulating effect which in fact allows the speed to adjust smoothly and progressively to the needs of the machining work to be performed.

The invention will now be described in detail with reference to the accompanying figures.

Fig. 1 is a schematic drawing for understanding the operation of the device; the cylinders are shown in line for the sake of clarity, which is functionally correct but does not correspond to the coaxial embodiment of the device, detailed in FIG. 2. To simplify the understanding of the basic principle, only one control valve S1, a restriction R1 and a non-return valve A1 have been shown.

Fig. 2 shows a section of the actuator in a plane passing through the axis of the device, with the adjustment members symbolically represented in order to better understand the operation of the device; this figure further shows the actuator connected to the external components of a typical control circuit.

Fig. 3 shows a section of the actuator according to a plane passing through the axis and according to an alternative embodiment of the device, wherein the members are shown in accordance with their real appearance.

Fig. 4 shows in detail the peripheral grooves 8 dug in the intermediate tube 20, covered by the crimped outer tube 19, thus forming channels for the return of the oil on the left side of the hydraulic piston and towards the reservoir 15.

The actuator consists of four main compartments, namely:

1) a pneumatic cylinder;

2) a hydraulic cylinder located coaxially inside the pneumatic piston;

3) an adjustment compartment;

4) an oil tank.

Hereinafter is described the operation of the actuator in the case of linear motion.

An external directional valve with pneumatic or electromagnetic control V is connected to the pneumatic cylinder. When the left side of the valve V is actuated by the solenoid Sg, the pneumatic piston Pp moves from left to right, causing in its movement the hydraulic piston Ph integral with the pneumatic piston by a mechanical connection at the end 1 1 of the rod 10 of the hydraulic piston. The compartment 9 decreases in volume as a result of the movement of the piston Ph, driving the oil through grooves 8 shown in FIG. 4 which open into a manifold 12. In FIG. 2 this oil return is simply shown symbolically by the line 17. The oil must then cascade two control valves and / or S2 and S1; a bypass 18 also makes it possible to connect the pipe situated between S1 and S2 to a reservoir 15 which serves both as an oil accumulator, as an expansion vessel and as a regulating member for the static pressure in the hydraulic circuit thanks to spring 16 and adjusting screw 1.

The oil having passed through these two valves S2 and S1 returns to the space situated on the left side of the hydraulic piston, the oil deficit due to the different sections of the two sides of the hydraulic piston being compensated by the pressurized oil stored in the hydraulic piston. tank 15.

A first phase of the left-to-right movement of the pistons is done at high speed, because the valves S2 and S1 let the oil pass freely. When the displacement of the end 1 1 of the rod 10, integral end of a not shown tool holder, is sufficient for the tool to approach the workpiece, an external position sensor S'1, judiciously placed in the purpose of informing the actuator of this approximation, electrically or pneumatically actuates the valve S1 by closing it, forcing the oil to pass through the restriction R1. A second phase of the movement begins at this moment; the pressure drop caused by this restriction, adjustable by a screw (represented by 14 in Fig. 3), causes an increase of the pressure on the right side of the hydraulic piston, slowing down the movement and allowing to adjust the speed in advance of the tool to a value appropriate to the machining work to be performed. If the resistance to movement increases, for example by the hardness of the workpiece, the speed will decrease more but the pressure drop in the restriction R1 will decrease accordingly, which ensures the self-regulating effect, thus conferring high precision and the desired softness for machining, without vibrations or chatter.

When this second phase of the movement is over, corresponding to the end of the machining pass, the position of the external pneumatic valve V is changed, which applies the pressure of the compressed air to the right side of the piston Pp, while the chamber 5 on the left side of the piston sees its pressure cancel by a passage to the atmosphere offered in the valve V. The pistons now move from right to left at high speed because the valve S1 was again placed in position opening (free passage), so the oil can circulate freely.

It is of course possible, by switching the control sequence of the valves S1 and S2, on the contrary, to perform a rapid initial movement from right to left followed by a regulated slow movement corresponding to a machining pass during the withdrawal of the piston, while the advance of the piston from left to right would be at maximum speed.

The pressure in the tank 15 can be adjusted at the beginning of the operations to a suitable value by the screw 1, in particular to avoid cavitation of the oil under any circumstances; this pressure will then be self-maintained by the overpressures generated by the pressure drops in the restrictions R1 and R2, according to the particular control of S1 and S2 depending on the chosen work cycle. Non-return valves A1 and A2 also provide protection against excessive overpressure resulting from improper control or failure of valves S1 or S2, so that the oil pressure can not be exceeded in any way. point the tank pressure 15.

The valves S1 and S2 have been symbolically represented in FIG. 2 for the sake of clarity. They can, however, be compact, functionally equivalent, as shown in FIG. 3. In this variant, the valves S1 and S2 have been functionally integrated into the directional valve 3, which can be driven pneumatically by means of the connections Y1 and Y2, or electrically by a solenoid integrated in the valve 3. is characterized by its flexibility, being able to perform the same functions described above for S1 and S2, by a proper adjustment of its internal components; the valve 3 may in particular comprise a reversible piston or reversible function, to fine-tune the movement from left to right with fast return from right to left, or vice versa, as already explained about the operation of the valves S1 and S2. The mode of operation of this variant is detailed below. Two external pneumatic directional valves V1 and V2, not shown in FIG. 3, are connected to the pneumatic cylinder. When the valve V1 is actuated, the pneumatic piston Pp moves from left to right, causing in its movement the hydraulic piston Ph integral with the pneumatic piston by a mechanical connection located at the end 1 1 of the rod 10 of the hydraulic piston. The compartment 9 decreases in volume as a result of the movement of the piston Ph, driving the oil through grooves 8 which open into a manifold 12, from which the oil can follow two paths, or pass through the valve 3 controlled by the pneumatic pilot valve 13, or through the valve 4 constituting an adjustable restriction by the screw 14. The oil having passed through these two valves 3 and / or 4 returns to the chamber located on the left side of the hydraulic piston, the deficit of oil due to the different sections on both sides of the hydraulic piston being compensated by the pressurized oil stored in the tank 15.

A first phase of the movement from left to right of the pistons is done at high speed because the valve 3 lets the oil pass freely. When the displacement of the end 1 1 of the rod 10, integral end of a not shown tool holder, is sufficient for the tool to approach the workpiece, an external position sensor, judiciously placed for the purpose of inform the actuator of this approximation, pneumatically actuates the pilot valve 13, which closes the valve 3 and forces the oil through the restriction 4. A second phase of the movement begins at this time; the pressure drop caused by this restriction, adjusted by the screw 14, causes an increase in the pressure on the right side of the hydraulic piston, slowing down the movement and thus making it possible to adjust the speed of advance of the tool to a value appropriate to the machining job to be performed. If the resistance to movement increases, for example by the hardness of the workpiece, the speed will decrease more but the pressure drop in the restriction 4 will decrease accordingly, which ensures the effect of self-regulation, thus conferring a high precision and the desired softness for machining, without vibrations or chatter.

When this second phase of the movement is complete, corresponding to the end of the machining pass, the external pneumatic valve V2 applies the pressure of the compressed air on the right side of the piston Pp, while the chamber 5 on the left side of the piston its pressure is canceled by the simultaneous control of the valve V1. The pistons now move from right to left at high speed, because the valve 3, subjected to this inversion of the hydraulic pressure, is constructed to offer the free passage of the oil in this condition, regardless of the position of the pilot valve 13.

The valve 3, in addition to being controlled by the valve 13, in fact also plays the role of a non-return valve. This valve 3 can be reprogrammed (reverse action) when it is desired instead to slow the movement from right to left. In another variant embodiment, this valve 3 can be bilateral. In another variant, the valves 3 and 4 can be combined into a single valve ensuring a proportional passage controlled by the valve 13. In another variant, it can also be electromagnetic instead of pneumatic.

The compartment 15 also acting as an oil reservoir is also a kind of expansion vessel, whose pressurization is obtained by the movement of the second phase forcing the flow of oil through the restriction 4, as it has been exposed above; the pressure in this compartment 15 is further maintained by the action of the spring 16 when the valve 3 is blocked. The compression of the spring 16, adjustable by the adjusting screw 1, in fact defines the level of pressure in the compartment 15, thus also the pressure in the compartment 9 to the right of the hydraulic piston, thus determining the resultant force on all the two pistons solidaires, so also the speed of movement of the pistons. This speed is in fact regulated by the regenerative self-regulating effect of the pressure drop in the restriction 4, a pressure drop which in turn depends on the speed.

Claims

A hydropneumatic actuator applicable to linear actuations, including arrangements for internally and regeneratively generating hydraulic pressure from the movement of the moving parts, thereby at the same time slowing down the movement by finely adjusting its speed when this is required by use, characterized in that the actuator comprises a ring-shaped pneumatic piston (Pp) provided with a movable tube (21) crimped into the internal bore of the piston, the pneumatic piston (Pp) being moving in an outer cylinder (Cy) under the effect of a pressure differential applied from the outside by pneumatic connections (X1, X2), the actuator being further provided with a coaxial hydraulic piston (Ph) provided a rod (10) sliding in a fixed coaxial liner (19, 20) separating the two pistons, the latter remaining secured to one another by a mechanical connection (1 1) between the end of the a rod (10) of the hydraulic piston and the end of the movable tube (21), the actuator further comprising two valves (S1, S2) electrically or pneumatically controlled, two adjustable restrictions (R1, R2) and two valves anti -return (A1, A2), an oil reservoir (15) maintained under pressure by a spring (16) adjustable by a screw (1), the tank being connectable through the valves (S1, S2), adjustable restrictions (R1, R2) and check valves (A1, A2) with both sides of the hydraulic piston (Ph). 2. Hydropneumatic actuator according to claim 1, characterized in that the valves (S1, S2) electrically or pneumatically operated are functionally integrated in a directional valve (3). 3. Hydropneumatic actuator according to one of claims 1 or 2, characterized in that the adjustable restrictions (R1, R2) and the check valves (A1, A2) are integrated in a single element (4) adjustable by a screw (14) located on the wall of the cylinder, this element being further easily removable. 4. hydropneumatic actuator according to one of claims 2 or 3, characterized in that reversibility means are implemented in the directional valve (3) or in the adjustable element (4) so as to slow the movement of pistons in one or other direction of movement depending on the type of work to be performed. 5. Hydropneumatic actuator according to one of the preceding claims, characterized in that the side of the hydraulic piston (Ph) surrounding the rod (10) of said piston is connected to the valves (S1, S2, 3, 4) through channels ( 8) integrated in the fixed coaxial liner (20).