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Title:
A LINEAR ACTUATOR
Document Type and Number:
WIPO Patent Application WO/2006/089554
Kind Code:
A1
Abstract:
A linear actuator comprising a housing (1) with a reversible electric motor (2) , which over a transmission (3) drives a spindle (4) with a spindle nut (5) , which is prevented from rotating , to which a tubular driving rod (6) is connected, which by the movement of the spindle nut (5) is displaced axial. The driving rod is guided in a protective tube (7) positioned in the housing, and on the outside of the protective tube there is a round going ring (8) , which is situated in a groove (9) in the housing. In the usual construction is the protective tube (7) held by at least one spring (10) between the ring (8) and an end stop (9a) in the groove. In the extreme position the spindle nut (5) moves against a stop in the protective tube and displaces it, so that the end of the protective tube (7) activates a micro switch, which cuts off the motor. However, there is a wish to use this type of actuator in constructions, where the actuator is being mounted by the protective tube (7) . For this purpose is the protective tube (7) fixated by using a rigid body (16,17) in at least one end of the groove (9) between the ring (8) and an end stop (9a, 9b) in the groove. In stead of the micro switch (15,19), which is activated by the displacement of the protective tube (7) , an end stop is used consisting with the ones used in actuators with a fixed protective tube, that is measurement of over current, encoders etc.

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Inventors:
Thomsen, Peter (Løkken 18, 2.t.h, Nordborg, DK-6430, DK)
Application Number:
PCT/DK2006/000109
Publication Date:
August 31, 2006
Filing Date:
February 24, 2006
Export Citation:
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Assignee:
Linak, A/s (Smedevægnet 8, Guderup, Nordborg, DK-6430, DK)
Thomsen, Peter (Løkken 18, 2.t.h, Nordborg, DK-6430, DK)
International Classes:
F16H25/20
Foreign References:
EP0647799A21995-04-12
US6321611B12001-11-27
GB779420A1957-07-17
EP0551197A11993-07-14
EP0647799A21995-04-12
Attorney, Agent or Firm:
Linak, A/s (Patent Department, P.O. Box 238, Aalborg, DK-9100, DK)
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Claims:
Claims :
1. A linear actuator comprising a housing (1) a reversible electric motor (2), which over a transmission (3) drives a spindle (4) with a spindle nut (5) connected to a tubular driving rod (6), which is axial displaced by the movement of the spindle nut, and which is guided in a protective tube (7) located in the housing, and where the protective tube has a round going ring (8) on the outside, which is located in a groove (9) in the housing c h a r a c t e r i z e d in that a rigid body (16,17) is located in at least one end of the groove (9) between the ring (8) and an end stop (9a, 9b).
2. An actuator according to claim 1, c h a r a c t e r i z e d in that the rigid body (16,17) is a bush, a piece of tube or a ring.
3. A linear actuator according to claim 1 or 2, c h a r a c t e r i z e d in that the rigid body (16) is situated in the groove being nearest to the free end of the protective tube (7) .
4. A linear actuator according to claim 1, 2 or 3, c h a r a c t e r i z e d in that there is a rigid body (16,17) on both sides of the ring (8) .
Description:
A Linear actuator

The invention relates to a linear actuator according to the preamble of claim 1.

Such an actuator is for instance known from EP 647 799 Bl Linak A/S . The actuator can be installed by using a mounting on the rear end and a front mounting on the front of the driving rod. However, in some situations one may wish to install the actuator by using a fitting around the protective tube. However, this is inconsistent with the end stop concept of the actuator, which is based on the fact that the protective tube can move axial against at least one coil spring. It is possible to let the housing move in proportion to the protective tube, but that would cause problems by the hanging of the actuator in the rear mounting.

The object of the invention is to provide a solution, so that the actuator can be installed by using the protective tube, and still leaves the overall structure of the actuator unchanged.

According to the invention this is achieved by the features of claim 1. The protective tube is fixated by replacing the coil spring with a rigid body, so that the actuator without further ado can be installed by use of the protective tube. Of course one misses out on the unique end stop, but instead the end stop types, normally used in actuators with a fixated protective tube, can be used. This could for instance be measurement of over current when the nut drives against a fixed buffer or potentiometer, optical or magnetic encoder or micro switches, which are activated by the spindle nut or the

driving rod. The solution has the advantage that the overall structure of the actuator remains completely unaltered, so that it is not necessary to invest in new tools and the assemble process remains the same except for the springs, which are replaced by rigid bodies.

The rigid body can for instance be bars, sheets, half shells, a grating structure depending on wishes and the conditions. It is particularly easy to use a bushing, a piece of tube or a ring, located over the protective tube. The rigid body is relatively small, and is preferably solid, but it can of course also be hollow.

In principle is it only necessary to rest one rigid body in the groove nearest to the free end of the protective tube. By that means the tube is locked in the outwards going direction, which usually is sufficient.

For an even more secure and strong fixing of the protective tube, a rigid body is located in both grooves. In that way the protective tube is locked in both directions .

A linear actuator according to the invention will be described in greater detail in the following with reference to the drawing in which,

Fig. 1, shows a longitudinal section through a known linear actuator,

Fig. 2, shows longitudinal section through a linear actuator according to an embodiment of the invention,

Fig. 3, longitudinal section through another known linear actuator, and

Fig. 4, longitudinal section through the linear actuator according to Fig. 3 embodied according to the invention.

The known actuator according to Fig. 1 consists of a plastic housing 1 in two parts with a reversible electric motor 2, which over a worm gear drive engages a spindle 4 with a spindle nut 5, whereto a driving rod 6 (also known as inner tube) is connected, surrounded by a protective tube 7, which acts as a guide the driving rod 6.

The protective tube 7 is equipped with a ring 8 located in a round going groove on the outside of the protective tube. The ring 8 is situated in a groove 9 in the housing. Between the ring 8 and one end 9a of the groove is a spring 10, and a corresponding spring 11 is positioned on the other side between the ring 8 and the other end of the groove. The actuator is assembled in the structure in which it is supposed to be built in by means of a rear mounting 12, which is installed in the rear end of the housing 1 and a mounting 13 in the free end of the driving rod 6. When the actuator is built in the mounting 13 will prevent the spindle nut 5 from rotating, so that it moves up and down the spindle 4 instead, depending on the rotary direction of the motor. In the fully retracted position of the driving rod the spindle nut hits a ring 14 situated in a groove inside the protective tube 7. The spindle nut 5 will then push the protective tube 7 into the actuator against the spring 11, which causes a bevelled end of the protective tube 7 to activate a micro switch 15, which cuts off the electric supply to the motor. When the driving rod 6 moves outwards the spring

11 will push the protective tube 7 back into its initial position, where it is being held in a neutral position between the two springs 10,11. When it reaches its extreme position, the spindle nut 5 will hit the edge of an end stop 15 in the protective tube 7, which serves as a guide for the driving rod 6. In this extreme position the spindle nut 5 draws the protective tube 7 out against the spring 10. This causes the innermost end of the protective tube to let go of a second micro switch (hidden behind micro switch 15) , which cuts off the electric supply to the motor. Both micro switches are mounted on a joint printed circuit board and connected to a wire with a DIN plug 20 for connection of a control box with power supply and operating circuit. When the spindle nut 5 moves inwards, the protective tube 7 is pushed back into the initial position by the spring 10.

The design of the actuator according to the invention is shown in Fig. 2. from where it appears that the two springs 10,11 have been replaced by two plastic- or light-alloy metal rings 16-17. The two rings fixate the protective tube 7, so that it is locked against movement in axial direction. It is therefore possible to install the actuator by using the protective tube 7, for example with a fitting 18 as indicated.

The two micro switches being used as end stop switches might then be avoided and as mentioned in the introduction a traditional end stop concept can be used instead, such as measurement of over current when the nut drives against a fixed buffer or potentiometer, optical or magnetic encoder or micro switches, which are activated by the spindle nut or the driving rod.

As mentioned is the structure of the actuator otherwise completely unchanged. In addition to the advantages mentioned earlier, it has the advantage that the existing approvals of the actuator also apply to the modified construction according to the invention. There are important advantages connected to this, as the actuator is often used in the hospital- and care sector.

Another known construction of an actuator is exposed in Fig. 3. This construction only differs from the one in

Fig. 1 by the end stop in the inwards direction of the driving rod 6. In that construction the spindle nut 5 moves completely or partly out of the protective tube 7 and activates one of the micro switches 15 directly, that is there is no stop for the spindle nut 5 in the protective tube 7 in the inwards direction, and there are also no springs, instead the ring 8 on the protective tube hits the end wall 9a in the groove directly. The end stop in the outwards direction of the driving rod 6 is identical to the construction described in Fig. 1, where the end of the protective tube 7 leaves a micro switch 19 and is pressed back by the spring 10.

The construction of this actuator according to the invention is shown in Fig. 4, from where it appears that the spring 10 has been replaced by a ring 16. The protective tube 7 is hereby fixed, as the ring 8 is being held between the end wall 9a in the groove and the ring

16. From this it appears as well, that the construction of the actuator in essentials is the same as the original construction in Fig. 3.