GB2196758A - Hydraulically controlled actuator - Google Patents

Abstract

A hydraulically controlled actuator 1A, B or C controlled by an individual adjustable vane pump 2 needs no valves in its piping and because it has no valves it can use sea water as a hydraulic fluid without suffering from cavitation problems. A controller 29 comprises a demand signal at 30 with a feed back signal at 29 to displace the axis of rotation of the vane pump to produce a variable flow to the actuator 2. A plurality of actuators may be adjusted by a plurality of pumps 2 operated by a common motor 24. One vane pump 2N is used as a supply pump and feeds fluids into the other pump actuator systems. <IMAGE>

Description

SPECIFICATION Hydraulically controlled actuator This invention relates to hydraulically controlled actuators.

Many known hydraulically controlled actuators use valves to control the pressure applied to an actuator by a pressure source such as a pump. Such systems inevitably have a degree of complexity and associated expense. Also because of problems of cavitation and wiredrawing effects only a few liquids, such as low vapour-pressure oils, can be used as an operating fluid in these systems.

This invention arose in an endeavour to reduce these problems.

This invention provides apparatus comprising an actuator controlled by a vane pump, the vane pump having a pumping chamber with inlet and outlet ports leading to the actuator and divided into a plurality of segments by vanes which are mounted so that they can be made to rotate relative to the chamber, and a flow control mechanism arranged to displace the axis of rotation by a variable amount and direction from a neutral position to produce a variable flow between the ports; and a sensor co-operating with the actuator and having an output connected to control the displacement mechanism.

Such a system can be built without the need for valves which may be expensive, produce cavitation and wire drawing effects. In contrast reversible vane pumps can be obtained inexpensively and are simple enough that one can be provided for each actuator (in a multi-actuated system) without making the system too expensive.

Where a plurality of actuators are used and each has an associated vane pump all the pumps may advantageously be driven by a single shaft passing through the axes of rotation of their vanes. Only one power source is then required to operate all the actuators.

Advantageously an extra pump can be driven by the same shaft and used to pump fluid to prime the other pumps and to fill the associated hydraulic systems linking them to the actuators. This also allows fluid lost by leakage to be replaced while the apparatus is in operation and allows rapid bleeding of the apparatus if air, or other contaminants, are present in the hydraulic fluid.

Where all the pumps are driven by a common shaft it may be particularly convenient to arrange them in a stack with abutting faces clamped together.

Preferably each pump includes a cam ring closed at each side by an end plate, the end plates defining the abutting faces. This allows a stack of any number of vane pumps required for a particular purpose to be built up as a series of identical standard modules.

It is preferred that adjacent pumps in the stack share an end plate between them because this allows the stack of pumps to be made lighter, smaller and cheaper.

A system employing the invention will now be described with reference to the accompanying figures in which; Figure 1 shows a submersible robot manipu lator employing actuators controlled by vane pumps, partly in perspective and partly in diagramatic form; and Figure 2 shows a sectional view of a vane pump used in the manipulator of figure 1.

Referring to Fig. 1, the manipulator includes a number of actuators 1 of which just three are illustrated at 1A, 1B and 1C respectively.

Each actuator is controlled by a respective vane pump 2, these pumps being arranged in a stack and being separated from each other by end plates 3, the latter having bores opening at ports 4 and 5 and forming inlet and outlet passages to the pumps. The ports 4 and 5 are connected by hydraulic lines 6 and 7 to the actuators 1.

Referring now to figure 2 each vane pump 2 comprises a central rotor 8 driven by a shaft 9 through its centre. The rotor 8 contains six slots 10 disposed symmetrically around its circumference. Each slot 10 contains a vane 11.

The rotor 8 is surrounded by a cam ring 12, and the vanes 11 are forced into contact with the inner surface of the cam ring 12 by springs 13 inside the slots 10. A pumping chamber 14 is formed by the space between the cam ring 12 and the rotor 8. Hydraulic fluid can pass in and out of chamber 14 through ports 15 and 16 defined by the inner ends of the aforementioned bores in the end plates.

In order for the vane pump 2 to control the actuator 1 it is necessary to be able to move the cam ring 12 relative to the rotor 8. This is achieved by a threaded rod 18 connected to the cam ring 12 and co-operating with an internally threaded spindle 19 connected to a stepper motor 20. The cam ring 12 can be moved to either side of a position where it is co-axial with the rotor 8 by stepping the motor 20 in either direction. This movement will be along the axis X in figure 2. Movement perpendicular to this axis will be prevented by two thrust blocks 21 and 22.

The vane pump 2 has a protective enclosure 23; and the motor 20 is mounted on the outside of this enclosure to allow easy access for repairs and maintenance.

The ends of the pumping chamber 14 are sealed by the plates 3. The pumps 2 and plates 3 are arranged so that each pump 2 has one plate 3 linking its pumping chamber 14 to the corresponding pair of hydraulic lines 6 and 7 and sealing one end of the pumping chamber 14 while a second plate 3 simply seals the opposite end of the pumping chamber 14.

One vane pump 2N does not control an ac tuator: instead it is used to prime and bleed all the hydraulic systems on the manipulator.

Ali of the vane pumps 2 are driven by an electric motor 24 which rotates the shaft 9 and is secured to the vane pumps 2 by a mounting flange 24A. The motor 24, vane pumps 2 and plates 3 are all clamped together into one unit by bolts 25 which pass through them all and are secured by nuts 26.

Each actuator 1 has a position sensor 27 which supplies data, giving the position of the actuator 1, along a line 28 to a controller 29.

In operation the controller 29 receives data along a line 30 defining the positions to which the actuators 1 must be moved. The controller 29 compares this data with the data from the position sensors 27, giving the current positions of the actuators 1, and sends signals along lines 31 to step the stepper motors 20 so that the pumps 2 move the actuators 1 towards their new positions. The controller 29 monitors the positions of the actuators 1 continuously and steps the stepper motors 20 appropriately to move the actuators 1 to their new positions and stop them there.

The hydraulic fluid used is sea water. When the manipulator is first immersed in the sea the vane pump 7N sucks in sea water through a filter 32. The filtered sea water is then pumped along a line 33 and lines 34 then through non-return valves 35 to fill the lines 6 and 7, actuators 1 and vane pumps 2 with water. In order to aliow this, bleeding vents 36 are opened by signals along a line 37 from controller 29 so that air can leave the systems. Once bleeding has been carried out the vents 36 are closed and the manipulator is ready to function.

While the manipulator is operating the pressure in the lines 34 is kept constant so that if the pressure drops in the lines 6 or 7, due to small leaks for example, water will be forced into the lines 6 or 7 through the non-return valves 35 and replace the lost water. The pressure in the lines 33 and 34 is monitored by a pressure sensor 38 connected to the controller 29 along a line 39. The controller 29 steps the stepper motor 20 (not shown) of pump 7N in such a way as to keep the output pressure of pump 7N as monitored at 38 constant at some pre-set level. This level will be pre-programmed into the controller 29.

Such a system could of course be used with many hydraulic fluids other than sea water, substituting a reservoir for the filter 32 if necessary.

Claims (8)

1. Apparatus comprising: an actuator controlled by a vane pump, the vane pump having a pumping chamber with inlet and outlet ports leading to the actuator and divided into a plurality of segments by vanes which are mounted so that they can be made to rotate relative to the chamber, and a flow control mechanism arranged to displace the axis of rotation by a variable amount and direction from a neutral position to produce a variable flow between the ports; and a sensor co-operating with the actuator and having an output connected to control the displacement mechanism.

2. Apparatus according to claim 1 comprising a plurality of actuators, a plurality of vane pumps as defined in claim 1, and a plurality of sensors each co-operating with an associated actuator and having an output connected to control the displacement mechanism of an associated pump; the pumps being driven by a common shaft extending along the axes of rotation of the vanes.

3. Apparatus according to claim 1 or 2 comprising another pump driven by a shaft which also drives the first mentioned pump or pumps and arranged to pump fluid into the latter and into the or each associated actuator and connectors thereto.

4. Apparatus according to claim 2 or claim 3 when dependent on claim 2 in which the pumps are arranged in a stack and have abutting faces clamped together.

5. Apparatus according to claim 5 in which each pump comprises a cam ring closed at each side by an end plate and the end plates defining the said abutting faces.

6. Apparatus according to claim 5 in which adjacent pumps share an end plate between them.

7. Apparatus according to claim 5 or 6 in which each cam ring is contained in a housing and in which the housings and the end plates are clamped together to form the stack.

8. Apparatus substantially as shown in figure 1 of the accompanying figures and substantially as described with reference thereto.