Technical field

The invention relates to a linear actuator comprising an electric motor, a transmission, a spindle, a spindle nut, a housing, an outer tube and an inner tube, the outer tube being connected to the housing, the spindle being interconnected to the transmission, the spindle nut being arranged on the spindle and the inner tube being connected to the spindle nut. The spindle nut and the inner tube is guided inside the outer tube and moved along the longitudinal axis of the spindle and thereby in or out of the outer tube depending on the direction of rotation of the electric motor. The linear actuator comprises an activation pin guided inside the outer tube and an electric switch, which can be activated by the activation pin. Background

Linear actuators are widely used for various applications in a number of industries and sectors including the hospital and care sectors.

When the spindle nut, during operation, has reached an end position of the stroke length, further operation of the motor in the same direction could be dangerous. In extreme cases, such a further movement of the driven element could destroy the linear actuator. To avoid damaging the actuator, an end stop arrangement is provided. When the spindle nut and thereby the inner tube reaches an end position, a switch is activated, which stops further operation of the electric motor.

In a prior art linear actuator, the end stop arrangement comprises a first end switch arranged at a first end of an outer tube and a second end switch arranged at a second end of an outer tube. Both end switches are mounted on a printed circuit board. The printed circuit board therefore requires a considerable length and takes up much space inside the outer tube, see e.g. WO02/292284 A1 to LINAK A/S. As shown in WO2012/083951 A1 to LINAK A/S, it is also common to have the end switch arrangement integrated in a housing or cabinet of the linear actuator. Such constructions also take up much space.

The general object of the present invention is to reduce the built-in dimen- sions of a linear actuator.

A further object of the present invention is to provide an end stop arrangement with a reliable activation of an electric switch for the end stop. A further object of the present invention is to provide a linear actuator with a motor, transmission and spindle being coaxially arranged.

A further object of the present invention is to provide a linear actuator, which is configured to be retrofitted at various locations on equipment for use in the hospital and care sectors.

The above objects will be evident from the below detailed description. According to an embodiment of the present invention, this is achieved by the linear actuator comprising:

- the linear actuator comprises an end stop arrangement having a fixed housing part and a moveable housing part arranged next to the fixed housing part,

- where the moveable housing part can be displaced relative to the fixed housing part,

- a spring arranged in a cavity formed by the fixed housing part and the moveable housing part,

- where the moveable housing part is arranged in engagement with the activation pin. The end stop arrangement has a simple design which is easy to assemble as the spring is held in the cavity of the two housing parts. The end stop arrangement also takes up very little space which enables a small built-in dimension of the linear actuator. In an embodiment, the moveable housing part comprises a protrusion, which engages a hole in the activation pin. Hereby, the activation pin can be arranged inside the outer tube before these are assembled with the spindle nut and the housing of the linear actuator.

The moveable housing part and the activation pin can be embodied as one component and thus saving costs by integrating two components in one and by simplifying the assembly.

In an embodiment, the linear actuator comprises a printed circuit board and the fixed housing part comprises means for fastening the fixed housing part to the printed circuit board. Hereby, the fixed housing part is immoveable. In an embodiment, the linear actuator comprises two electric switches, one for each end stop on the spindle.

In an embodiment the fixed housing part comprises a guide for the moveable housing part. This ensures that the moveable housing part can only travel along the path of the guide. The moveable housing part will therefore always activate one the switches when it is displaced.

In an embodiment the spindle nut comprises a collar with a front end and a rear end and where the moveable part comprises a flange for engagement with the rear surface of the collar of the spindle nut. Since the spindle nut is held against rotation, the flange ensures engagement with the spindle nut when this end stop is reached.

In an embodiment the activation pin comprises a projection for engagement with the front end of the collar of the spindle nut. Hereby, the spindle nut 81 will only engage the activation pin when the end stop is reached. In an embodiment, the fixed housing part comprises a support leg bridging the moveable housing part. This ensures that the moveable housing part is held in place. In an embodiment, the two electric switches are placed on each side of the support leg of the fixed housing part.

Detailed description

The invention will now be explained in further detail below by exemplary embodiments and with reference to the schematic drawing.

Fig. 1 A-1 B show a linear actuator.

Fig. 2 shows a cross-sectional view AA of the linear actuator according to a preferred embodiment of the present invention.

Fig. 3 shows a first perspective view of the housing according to a preferred embodiment of the present invention. Fig 4 shows a second perspective view of the housing for the linear actuator according to the present invention.

Fig 5 shows a first side view of the housing. Fig 6 shows a second side view of the housing.

Fig 7 is an exploded view showing the drive line of the linear actuator according to a preferred embodiment of the present invention.

Fig 8 shows a perspective of end stop arrangement, the spindle, and the spindle nut. Fig. 9 shows an exploded view of the fixed housing part, the moveable housing part, and the spring.

Fig. 10 shows a perspective of the fixed housing part seen from the bottom. shows a perspective of the moveable housing part seen from the top. Fig. 12 shows a perspective of the end stop arrangement with the electric switches. shows a side view of the end stop arrangement, spindle, and spindle nut, where the spindle nut is in a position of the spindle nearest the electric motor.

Fig. 14 shows a side view of the end stop arrangement, spindle, and spindle nut, where the spindle nut is in a position of the spindle furthest away from the electric motor.

Fig. 1 A and 1 B show a linear actuator 1 comprising an outer tube 3 and an inner tube 2. The housing 10 consists of a first housing part 1 1 and a second housing part 12. The housing is provided with a gasket (not shown) for preventing water or dust from entering the interior space of the linear actuator 1 .

The linear actuator of the present invention is used in furniture (e.g. hospital beds or domestic beds) or a wheel chair. For mounting the linear actuator, the rear end of the housing is equipped with a rear mounting 6, and the outer tube 3 is connected to a front mounting 5. The rear mounting 6 and front mounting 5 are pivotally connected to two individual elements on the piece of furniture or wheel chair. The linear actuator 1 comprises an electric motor 20, typically a reversible electric motor, which can be either a DC or an AC motor for low voltage or mains voltage. The linear actuator 1 comprises a socket 4 for connecting the linear actuator 1 to a power supply or an electric controller (not shown in the drawings).

In Fig. 2, the electric motor 20 is connected to a transmission 40, and the coupling interconnects the transmission and the spindle 80. The spindle 80 has a first end 61 connected to the transmission 40 via an Oldham coupling 30 for accommodating a parallel misalignment between the spindle 80 and the transmission 40.

The linear actuator 1 further comprises a spindle 80 driven by the electric motor 20 through a transmission 40, preferably a planetary gear. The spindle 80 is connected to the transmission via a coupling 30, such as an Oldham coupling, which can accommodate for parallel misalignments. The electric motor 20, the transmission 40 and the outer tube 3 are coaxially arranged. Fig. 2 shows an outer tube 3 connected to the housing 10, and the inner tube 2 is connected to the spindle nut. The spindle nut and the inner tube 2 are guided inside the outer tube 3.

Fig. 2 shows a cross-sectional view of the linear actuator 1 comprising a spindle 80, a spindle nut 81 , a housing 10, an outer tube 3 and an inner tube 2. The spindle nut 81 is arranged on the spindle 80 which is connected to the transmission 40. The outer tube 3 is connected to the housing 10 and the inner tube 2 is connected to the spindle nut 81 . The spindle nut 81 is secured against rotation and guided inside the inner tube 2. The inner tube 2 is guided inside the outer tube 3.

The spindle nut 81 has internal threads 82 for engaging the external threads The spindle nut 81 is guided inside the inner tube 2 and is secured against rotation.

Activation of the electric motor 20 will, via the transmission 40, cause the spindle 80 to rotate, whereby the spindle nut 81 and front mounting 5 will travel along the longitudinal axis of the spindle 80 in a direction depending on the direction of rotation of the electric motor 20. The sealing element 50 is arranged between the outer tube 3, the housing 10 and the retaining element 60.

Figs 3-6 show the second housing part 12 of the housing having a tubular section 14 with an opening for receiving the outer tube 3, and the opening of the tubular section 14 has an inclined inner surface 13. The inclined inner surface constitutes the contact surface as the inclined inner surface is en- gaging the sealing element 50 when the linear actuator is assembled.

The second housing part 12 of the housing is provided with a number of connecting elements 16 complementing the recesses in the retaining element 60. The outer tube 3 has a circular or a polygonal geometry comprising four side walls forming a rectangular shape preferably with rounded corners.

The retaining element 60 is connected to the housing 10, the retaining element being configured for retaining the sealing element 50 relative to the housing 10.

Figs. 2 and fig. 7 show the drive train of the present invention, where the drive train comprises an electric motor 20 having an output shaft 21 being connected to the transmission input end of the transmission 40. The transmission 40 includes a transmission housing 41 , a transmission input end and a transmission output end positioned opposite the transmission input end. The transmission input end is constituted by a sun gear 45 and the output end is constituted by a planet carrier 46. Referring to Figs. 2 and 8 to 14, the linear actuator 1 comprises an end stop arrangement comprising a fixed housing part 85, a moveable housing part 86, and a spring 87 arranged in a cavity 85', 86' commonly formed by the two housing parts 85,86. The fixed housing part 85 is connected to the printed circuit board 88 with snap connections 89 and is thus immoveable. The spring 87 is partly arranged in a cavity 85' of the fixed housing part 85. The moveable housing part 86 also comprise a cavity 86' in which the spring 87 is partly arranged. The moveable housing part 86 is arranged next to the fixed housing part 85, such that the two cavities 85', 86' of the housing parts 85,86 align with each other. In this position the spring 87 is in a resting position. The spring 87, the moveable housing part 86 and the main portion of the fixed housing part 85 are positioned such that their longitudinal axes are parallel with the longitudinal axis of the spindle 80. The moveable housing part 86 can be displaced relative to the fixed housing part 85 along these longitudinal axes. The fixed housing part 85 has a support leg 90 extending perpendicularly to the main portion, which bridges the moveable housing part 86. Hereby, the moveable housing part 86 is held slideably in place against the printed circuit board 88 and the fixed housing part 85. Two electric switches 91 ,91 ' are placed on each side of the support leg 90 of the fixed housing part 85 such that the moveable housing part 86 can activate the switches 91 ,91 ' when this is displaced.

An activation pin 92 is arranged inside the outer tube 3. An end of the activation pin comprises a hole 93 engaging a protrusion 94 of a flange 95 of the moveable housing part 86. It is noted that the activation pin 92 and the moveable housing part 86 could be embodied as a single component. The spindle nut 81 has a collar 96 with a front end 98 facing the front mounting 5 and a rear end 99 facing the rear mounting 6. When the spindle nut 81 reaches the end of the spindle 80 nearest the electric motor 20, the rear end 99 of the collar 96 of the spindle nut 81 engages the flange 95 of the moveable housing part 86 and displace it in a direction towards the electric motor 20. Hereby, the moveable housing part 86 is displaced in a direction towards the electric motor 20 and causes an activation of the electric switch 91 ' nearest the electric motor 20. This causes the controller of the linear actuator 1 to stop the electric motor 20. The end of the activation pin opposite the hole 93 comprises a projection 97 extending towards the spindle 80. When the spindle nut 81 reaches the end of the spindle 80 furthest away from the electric motor 20, the front end 98 of the collar 96 of the spindle nut 81 engages the projection 97 of the activation pin 92. Hereby, the moveable housing part 86 is displaced in a direc- tion away from the electric motor 20 and causes an activation of the electric switch 91 furthest away from the electric motor 20. This causes the controller of the linear actuator 1 to stop the electric motor 20.

When the switches 91 ,91 ' are activated the spring 87 will be compressed and thus be in a tensioned state. When the spindle nut 81 is moved out of one of the end positions on the spindle 80, the collar 96 of the spindle nut 81 disengages from its contact with either the moveable housing part 85 or the activation pin 92. This will allow the spring 87 to release its potential energy and displace the moveable housing part 86 into a position where the spring 87 is in a resting position, i.e. where none of the electric switches 91 ,91 ' are activated.

It should be noted that the end stop positions on the spindle 80 does not have to be at the respective ends of the spindle 80. The threaded portion 83 of the spindle 80 does therefore not necessarily reflect the stroke length of the linear actuator 1 . Hence, the linear actuator 1 can be designed to have a stroke length, which is shorter than the length of the threaded portion 83 of the spindle 80. Reference numbers

In the following is given a list of reference numbers that are used in the detailed description of the invention. linear actuator 1

inner tube 2

outer tube 3

socket 4

front mounting 5

rear mounting 6

housing 10

first housing part 1 1

second housing part 12

inclined inner surface 13

tubular section 14

connecting elements 16

electric motor 20

output shaft 21

coupling 30

transmission 40

transmission housing 41

planet carrier 46

sealing element 50

retaining element 60

spindle 80

spindle nut 81

threaded spindle portion 82

external threads 83

spindle end 84

fixed housing part 85

moveable housing part 86

spring 87

cavity 85', 86' printed circuit board 88

snap connection of fixed housing part 89

support leg of fixed housing part 90

Electric switch 91

Activation pin 92

Hole of activation pin 93

Protrusion of the flange of the moveable housing part 94 Flange of the moveable housing part 95

Collar of spindle nut 96

Projection of the activation pin 97

Front end of collar of the spindle nut 98

Rear end of collar of the spindle nut 99