The present invention relates to a linear actuator comprising a console, an outer tube connected to the console, an electric motor, a transmission, and a spindle connected to the transmission, a spindle nut on the spindle, an inner tube connected to the spindle nut. The spindle nut and the inner tube are guided inside the outer tube. The electric motor comprises a motor housing and a rotor with an output shaft. The linear actuator is controlled by a control unit having a printed circuit board. Moreover, the linear actuator comprises a sensor arrangement comprising a first part and a second part, and where the first part is connected to the rotor and the second part is mounted on a sensor section of the printed circuit board.

The operation of the linear actuator is controlled by the control unit, which supplies electric power to the electric motor. To enhance the precision of the linear actuator, these often provide information of the amount of work done by the electric motor. This information can e.g. be in the form of counting the number on revolutions of the motor, which can be used to calculate the position of the spindle nut on the spindle. To this end, different kind of sensors can be arranged in the linear actuator. Such sensors are commonly difficult to integrate in the linear actuator as they take up space and are typically cabled from the motor to the control unit. Furthermore, they increase the complexity of the assembly of the linear actuator.

The object of the invention is to provide a linear actuator with a simpler sensor arrangement.

This object is solved with a linear actuator according to the preamble of claim 1 , where the motor housing comprises an opening through which the sensor section protrudes into the motor housing. The information of the motor needed for controlling the motor can be directly obtained by the sensor arrangement. The second part of the sensor arrangement can be positioned sufficiently close to the first part of the sensor arrangement, so that the second part can obtain the information from the first part. The sensor arrangement is in particular suitable for detecting an angular position of the rotor with respect to the motor housing and consequently to count, for example, rotations performed by the rotor of the motor. Since the second part of the sensor arrangement is directly mounted on the printed circuit board, the information obtained by the sensor arrangement is directly available to the control unit.

In an embodiment of the invention, the opening is at least partly in the form of a slit. The sensor section of the printed circuit board is part of the printed circuit board and therefore rather flat. Using a slit keeps the remaining space between the sensor section of the printed circuit board and the motor housing as small as possible. Ingress of undesired particles, such as dust, can be kept at a minimum.

In an embodiment of the invention, the first part is a magnet arrangement. The magnet arrangement can, for example, have a magnet with a pair of poles. It is also possible to use more than one pair of poles.

In an embodiment of the invention, the electric motor comprises a top part and a bottom part at the opposite end, and the first part of the sensor arrangement is positioned at the bottom part. Thus, integrating the sensor arrangement in connection with the output shaft, where only little space is available, is avoided.

In an embodiment of the invention, the first part is arranged at a shaft section protruding out of a stator of the electric motor. Hereby, the magnetic fields, which develop between the stator and the rotor of the electric motor, do not influence the sensor arrangement. In an embodiment of the invention, the electric motor comprises a shaft bearing arranged at the bottom part of the electric motor, and the first part of the sensor arrangement is arranged between the stator of the electric motor and the shaft bearing. In this position, the shaft of the electric motor is in a stable and clearly defined position, so that the sensor arrangement is able to provide the required information in a continuous and stable manner.

In an embodiment of the invention, the linear actuator comprises a sensor section, and the printed circuit board is embedded in the control box, and the sensor section protrudes out of the control box. The rest of the printed circuit board is protected by the control box. The sensor section of the printed circuit board is positioned within the housing of the electric motor. Therefore, the printed circuit board is completely protected.

In an embodiment of the invention, the motor housing comprises a socket with at least two contact pins and the control box comprises a corresponding counterpart. It is therefore simple to establish a connection between the control box and the electric motor. The counter elements of the control box are connected to the contact pins of the motor housing. At the same time, the sensor section of the printed circuit board is inserted into the motor housing, so that all parts are in place after a single simple assembly operation.

In an embodiment of the invention, the control box and the motor housing are connected by means of a snap connection. The snap connection is a simple way to connect the control box and the motor housing.

In an embodiment of the invention, the control box comprises a hook, and the console comprise a counterpart to the hook, and where the hook and the counterpart to the hook constitute the snap connection. The control box can hereby be connected to the remaining parts of the linear actuator by a single and simple operation.

In a further embodiment, the hook of the control box is resilient.

In an embodiment of the invention, the counterpart to the hook is an eye in the front end of the console.

In an embodiment of the invention, the snap connection is releasable. Hereby, the control box can be disengaged and engaged again without damaging the snap connection

In an embodiment of the invention, the control box is fixed to the motor housing by means of a screw arrangement. In particular when the linear actuator is exposed to rough conditions, for example during transportation, the snap connection is in some cases not sufficient to keep the control box secured to the control box. In such a case, a screw connection can additionally be used. It is only necessary to provide a screw in the holes of the motor housing aligned with the corresponding holes in the control box. Other fastening means other than screws can also be used.

A preferred embodiment of the invention will now be described in more detail with reference to a drawing, wherein:

Fig. 1 shows a perspective view of a linear actuator,

Fig. 2 shows a perspective view of a linear actuator with a longitudinal partial section,

Fig. 3 shows a front view of a linear actuator, Fig. 4 shows a perspective view of the linear actuator with the control box,

Fig. 5 shows an exploded view of the parts of a linear actuator,

Fig. 6 shows a side view of the parts shown in Fig. 4,

Fig. 7 shows a cross section through a part of the linear actuator,

Fig. 8 shows an enlarged view of a detail of the rear end of the electric motor, and

Fig. 9 shows a bottom view perspective of the linear actuator with the control box.

Fig. 1 shows a perspective view of a linear actuator 1 comprising a console 2, an outer tube 3 and an inner tube 4 guided in this. For mounting the linear actuator, a rear end is equipped with a rear mounting 5 and a front end is equipped with a front mounting 6 at the free end of the inner tube 4. As it appears from both Fig. 1 and Fig. 2, the linear actuator 1 comprises an electric motor 7, typically a reversible electric motor, which can be either a DC or AC motor for low voltage or mains voltage. The electric motor 7 is mounted to the bottom of the console 2 and the rear mounting 5 is mounted at the rear end of the console 2.

The linear actuator 1 comprises a socket 8 for connecting the linear actuator 1 to a power supply or an electric controller.

The outer tube 3 comprises a rectangular section, in particular a square section, i.e. the outer tube 3 comprises four walls 9,10,1 1 ,12. The linear actuator 1 further comprises a spindle 13 driven by the electric motor 7 through a transmission 14, which is a worm gear, where an extension of the shaft of the electric motor 7 is designed as a worm 17 in engagement with a worm wheel 15, connected to the spindle 13.

A spindle nut 16 with internal threads engage with the external threads of the spindle 13. The spindle nut 16 is guided inside the outer tube 3 and is secured against rotation.

The front most part of the spindle nut 16 is adapted for receiving the inner tube 4. More specifically, the rear end of the inner tube 4 can be fastened to the spindle nut 16 via corresponding threads on both parts, or the spindle nut 16 can have a projecting edge or shoulder on which the inner tube 4 can be accommodated. Activation of the electric motor 7 will, via the transmission 14, cause the spindle 13 to rotate, whereby the spindle nut 16 and inner tube 4 will travel along the longitudinal axis of the spindle 13 in a direction depending on the direction of rotation of the motor 7.

The front end of the outer tube 3 comprises a bushing 17 for guiding the inner tube 4. The console 2 comprises a front side 18 with an opening 19 which is adapted to the cross section of the outer tube 3. Since the outer tube 3 has a rectangular or square section, the outer tube 3 is fixed against rotation with respect to the console 2.

The console 2 comprises a receiving part for the electric motor 7. Further, the console comprises a bearing 1 9 for the output shaft 20 of the electric motor 7. The output shaft 20 is embodied in continuation of the rotor 25 of the electric motor 7. The operation of the linear actuator is controlled by a control unit which is arranged within a control box 21 . The control unit comprises a printed circuit board. A sensor section 22 of the printed circuit board protrudes out of the control box 21 . The motor housing 23 comprises an opening 24 through which the sensor section 22 protrudes into the motor housing 23.

The electric motor 7 comprises a first part 26 of a sensor arrangement (Fig. 6). The first part 26 is, for example, in form of a magnet arrangement. The first part 26 can be, for example, a magnet with a pair of poles. However, it is possible to use a magnet arrangement with more than one pair of poles.

The first part 26 of the sensor arrangement is arranged at a shaft section 27 protruding out of a stator 28 of the electric motor 7. The first part 26 of the sensor arrangement is arranged between the stator 28 and a shaft bearing 29.

The sensor section 22 of the printed circuit board is provided with a second part 30 of the sensor arrangement. The second part 30 of the sensor arrangement can be, for example, a Hall sensor.

When the control box 21 is connected to the console 2 and the electric motor 7, the sensor section 22 of the printed circuit board is at least partly located in the motor housing 23 of the electric motor 7. The second part 30 of the sensor arrangement is located near the first part 26 of the sensor arrangement.

The opening 24 in the motor housing 23 can be formed as a slit. As can be seen in Fig. 3, the slit extends along the center line of the motor housing 23, which is convergent with the rotation axis of the rotor 25 of the electric motor 7.

The electric motor 7 comprises a top part 31 out of which the output shaft 20 protrudes and a bottom part 32 at the opposite end. Fig. 7 shows the bottom part 32 from a bottom view. The motor housing 23 comprises a socket 8 with two contact pins 33,34 and the control box 21 comprises a corresponding counterpart. The control box 21 comprises a resilient hook 35 at a side facing the console 2. When the control box 21 is mounted at the electric motor 7, the resilient hook 35 forms a snap connection with a counterpart 36 of the console 2. The counterpart 36 of the snap connection can be formed as an eye in the front side 18 of the console 2. The snap connection can be releasable so that the control box 21 can be disengaged from the console 2. In another embodiment, the counterpart 36 to the resilient hook 35 can be arranged on the outer tube 3.

In addition, the rear part 32 of the motor housing 23 can have two screw holes 37, 38 which are provided with the purpose of inserting screws 39, 40, so that the control box 21 can be connected to the electric motor 7 by means of screws 39, 40.

The information about the rotations of the motor is obtained directly by the sensor arrangement. Since the second part 30 of the sensor arrangement is directly placed on the printed circuit board in the control box 21 , the control unit receives the necessary information without needing an additional wiring.

In an embodiment, the first part 26 of the sensor arrangement can be a ring magnet and the second part 30 can be a Hall sensor. The sensor arrangement could for example also be designed using an optical sensor or a potentiometer.