GB2459297A

GB2459297A - Electrically driven linear actuator

Info

Publication number: GB2459297A
Application number: GB0807071A
Authority: GB
Inventors: John Wale
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-04-18
Filing date: 2008-04-18
Publication date: 2009-10-21
Also published as: GB0807071D0

Abstract

A linear actuator comprises first and second actuator elements, in which a first element 20 is coupled to an electric motor stator 1, an electric motor rotor 2 is rotatably drivable within the stator and is threadedly engaged with the second element 22, such that rotation of the rotor varies the separation of the first and second actuator elements. A bearing assembly 3, 7 may support the rotor relative to the first element, providing both radial and axial support to the rotor. The rotor 2 may be integral with or coupled to a drive portion or screw 6 which is threadedly engaged with the second element 22. A brake 5 and/or a rotary position sensor may be provided on the rotor 2. The second element 22 may be coupled to a nut 8 which may be prevented from rotating by means of a rail 9 and slider 10.

Description

Electric Monolithic Linear Actuator The invention relates to an actuator and a method in which linear movement is produced by a rotary electric motor driving a mechanical rotary-to-linear converter.

Background of the Invention

Linear actuators have many uses in factory automation, robotics and other motion control applications, since their well-defined force and speed characteristics acting in a straight line simplifies machine design and allows interchangeability between actuator types. Hydraulic, pneumatic and electro-mechanical technologies can be applied to linear actuators, but electro-mechanical types offer the lowest noise and least contamination and are therefore the most suitable for use in domestic and office environments.

Summary of the Invention

The invention provides a linear actuator and a method as defined in the appended independent claims, to which reference should now be made. Preferred or advantageous features of the invention are set out in dependent subclaims.

The rotor and stator of a brushed or brushless electric motor may thus be combined with the stationary and rotating parts of a ballscrew, rollerscrew or leadscrew mechanism to form a monolithic assembly. The main bearings preferably simultaneously provide reactive thrust for the screw mechanism and radial location for the rotor of the electric motor. By combining the motor and screw into one component and sharing the bearings between them, the resulting actuator may be made smaller, simpler, lower in cost and lower in positional error than the prior-art arrangement whereby the motor and actuator are separate components, interconnected by a mechanical coupling.

Description of Specific Embodiments

Embodiments of the invention will now be described by way of example, with reference to the accompanying drawing, in which: Figure 1 is a longitudinal section of a linear actuator according to a first embodiment of the invention.

Figure 1 shows the general form of a monolithic linear actuator according to a first embodiment of the invention. The actuator comprises first and second actuator elements 20, 22. Actuator element 22 is slidably mounted within actuator element 20, and is drivable so that the length of the actuator is variable. The two actuator elements carry couplings 13 at their respective ends for mounting the actuator.

The actuator comprises a motor consisting of a fixed part 1, or stator, and a rotating shaft part 2, or rotor. The stator is secured within a housing 24 of the first actuator element 20.

The rotating shaft is supported in bearings 3, 7 mounted within the housing on each side of the stator. The motor shaft extends through one bearing 7 to form a threaded rod or screw 6, which engages with a nut 8 coupled to the second actuator element 22. This is typically achieved through low-friction threaded surfaces or re-circulating balls, in a baliscrew or leadscrew mechanism. The nut is prevented from rotating within the housing 24 but is allowed to move axially along the screw by a linear guide consisting of a rail 9 which is fixed in relation to the actuator housing, or casing, 24 and a close-fitting, low-friction slider 1 0 which is attached to the nut. The remainder of the second actuator element comprises a hollow extension tube 11 attached to the nut, which can move axially through a guide aperture 26 at the end of the housing 24. The coupling, or rod end bearing, 13 is attached to the end of the extension tube.

It is important that the rotating shaft 2 is supported both radially, in order to locate it within the stator, and axially, in order to resist end loadings exerted by the engagement of the screw with the nut. In the embodiment, this is achieved by a single bearing or bearing assembly 7, mounted between the stator and the screw. This bearing assembly may comprise, for example, a pair of asymmetric bearings such as taper roller or angular contact ball types used in a back-to-back configuration to give high axial load capability.

This end of the actuator shaft, at the exit from the stator, may be termed the drive end.

The rotating shaft, or motor shaft, may also implement other functionality. For example, at the non-drive end, supported by the bearing 3, the shaft may extend from the rotor to a space in an end cap 4 of the casing 24 where one or more positional sensors may be located for the control of motor commutation and/or the measurement of actuator extension. The shaft may be further extended to couple to a rotary brake 5, allowing the actuator position to be locked as required.

In the embodiment described above, the rotating shaft is fabricated as a single monolithic or unitary structure, incorporating components from the brake 5, through the rotor 2, to the screw 6. The simplicity and rigidity of this structure may advantageously simplify construction of the actuator and improve its performance, by enhancing its rigidity.

Alternatively, the monolithic shaft may be fabricated from separate components, rigidly coupled together.

The rigid coupling may advantageously allow a rotary positional sensor to be driven in synchronism with the rotor and screw assembly. If a brake is provided, this may be applied to the shaft so as to give resistance to actuator movement when the motor is de-energised.

Claims

Claims 1. A linear actuator comprising first and second actuator elements, in which; a first element is coupled to an electric motor stator; an electric motor rotor is rotatably drivable within the stator and is threadedly engaged with the second element, such that rotation of the rotor varies the separation of the first and second actuator elements; and a bearing assembly supports the rotor relative to the first element, providing both radial and axial support to the rotor.
2. A linear actuator according to claim 1, in which the rotor is coupled to or carries a rotary position sensor.
3. A linear actuator according to claim 1 or 2, in which the rotor is coupled to a brake.
4. A linear actuator according to any preceding claim, comprising an angular sensor for determining the angle of the rotor relative to the first actuator element.
5. A linear actuator according to any preceding claim, in which the rotor forms part of a monolithic or unitary rotor shaft that extends both within the stator and in threaded engagement with the second element.
6. A linear actuator according to any preceding claim, in which the rotor is rigidly coupled, or is integral with, a drive portion that is threadedly engaged with the second element.
7. A linear actuator according to claim 2, in which the rotary position sensor is carried by a portion of a single rotor shaft or a shaft portion that is rigidly coupled to or integral with the rotor.
8. A linear actuator according to claim 3, in which the brake acts on a portion of a single rotor shaft or a shaft portion that is rigidly coupled to or integral with the rotor. 5,'
9. A linear actuator according to any preceding claim, comprising a linear position sensor for determining the position of the second element relative to the first element.
10. A method for operating a linear actuator to vary the separation of first and second actuator elements, comprising the steps of supporting a rotor portion of an actuating shaft for rotation relative to the first actuator element, such that the shaft is electrically drivable within a stator, and threadedly engaging a drive portion of the actuating shaft with the second actuator element, such that rotation of the shaft varies the separation of the first and second actuator elements.
11. A linear actuator substantially as described herein, with reference to the drawing.
12. A method for operating a linear actuator substantially as described herein, with reference to the drawing.