TECHNICAL FIELD

The disclosure relates to a magnet actuator comprising a first housing arrangement, a second housing arrangement, and a main magnet.

BACKGROUND

Electronic devices may be provided with magnet actuators in order to generate, e.g., sound waves for audio. Prior art magnet actuators comprise magnets which either attract or repulse each other. Initially, the magnets are arranged in force equilibrium, but in order to generate sound waves the attractive or repulsive force between the magnets is changed by means of an electric current passing through a coil located between the magnets, the current causing at least one of the magnets to move such that the distance between the magnets decreases or increases.

As disclosed in GB2532436, the magnets of the audio actuator may be interconnected by means of resilient support elements which counteract the attractive or repulsive force between the magnets such that the magnets and the resilient support element are in a force equilibrium state as long as no current is supplied. The different components of the audio magnet actuator of GB2532436 are integrated into the device structure and arranged between the main elements of the device.

The appearance of the assembled electronic device can be assessed only after the force equilibrium state has been reached, i.e. after the main elements of the device have been assembled. Any possible defects, caused by dimensional tolerance variations of each separate element in the structure, variations in force between the magnets, or variations in the force caused by the resilient support element, will be visible only after assembly, and will subsequently be time consuming and costly to repair. Furthermore, due to the conventionally high mechanical stiffness of the vibrating components of the electronic device, such as the display, which is necessary in order to make the electronic device sufficiently durable, the resonance frequency of audio magnet actuator is usually too high to be able to produce not only audio but also haptic feedback. Haptic feedback requires resonance frequencies low enough for users to sense them efficiently with their fingers. A conventional means for providing haptic feedback is using linear resonating actuators which can have resonance frequencies specifically tuned to 100- 200 Hz which facilitates haptic feedback efficiently.

SUMMARY

It is an object to provide an improved magnet actuator. The foregoing and other objects are achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description, and the figures.

According to a first aspect, there is a magnet actuator comprising a first housing arrangement comprising a first housing, a first balancing magnet, a first coil partially surrounding the first balancing magnet, and a first suspension means, a second housing arrangement comprising a second housing, a second balancing magnet, a second coil partially surrounding the second balancing magnet, and a second suspension means, a main magnet arranged between the first suspension means of the first housing arrangement and the second suspension means of the second housing arrangement, the main magnet being fixedly connected to the second suspension means, a first constant attractive force being generated between the first housing and the main magnet, the first balancing magnet and the main magnet being configured to generate a first constant repulsive force counteracting the first constant attractive force, such that the first housing arrangement and the main magnet are maintained in a force equilibrium state, a second constant repulsive force being generated between the second housing and the main magnet, the second balancing magnet and the main magnet being configured to generate a second constant attractive force counteracting the second constant repulsive force, such that the second housing arrangement and the main magnet are maintained in a force equilibrium state, the first coil and the main magnet being configured to generate a first alternating magnetic force, the second coil and the main magnet being configured to generate a second alternating magnetic force, wherein manipulating electrical current in the first coil causes a change in the first alternating magnetic force thereby causing displacement between the first housing arrangement and the main magnet, and/or wherein manipulating electrical current in the second coil causes a change in the second alternating magnetic force thereby causing displacement between the second housing arrangement and the main magnet.

A magnet actuator such as this, wherein a magnet and a housing are in a force

equilibrium state facilitates the manufacture of the electronic device in which the magnet actuator is placed. The attractive force caused by the magnet and the housing are balanced from the start, such that the other components of the electronic device remain unaffected by, e.g., variations in the force or dimensional variation of the different components of the magnet actuator. Such a solution reduces the number of defective electronic devices and hence manufacturing and repair costs. Furthermore, such a magnet actuator is sufficiently strong yet spatially efficient. Additionally, the dual action facilitates a magnet actuator which can be used over a wider range of resonance frequencies, such as for producing both sound waves and haptic feedback.

In a possible implementation form of the first aspect, the first alternating magnetic force and the second alternating magnetic force are one of an attractive force and a repulsive force, the first alternating magnetic force and the second alternating magnetic force being generated and/or changed independently or simultaneously, allowing vibrations to be produced by means of the housings in any desired, or both, directions along the center axis of the magnet actuator.

In a further possible implementation form of the first aspect, the first alternating magnetic force and the second alternating magnetic force are generated simultaneously, the first alternating magnetic force and the second alternating magnetic force both being attractive forces or repulsive forces, the main magnet being maintained in an equilibrium position between the first suspension means and the second suspension means, facilitating application of a first functionality by means of movement of the housings, such as generating vibrations within the higher resonance frequency interval, producing e.g. sound waves.

In a further possible implementation form of the first aspect, the first alternating magnetic force and the second alternating magnetic force are changed simultaneously, by different magnitudes, by manipulating the electrical current in the first coil and in the second coil, such that the first housing arrangement and the second housing arrangement are displaced at different resonance frequencies, allowing a wider interval of resonance frequencies to be generated, such as both sound waves and vibrations for haptic feedback and reducing the space needed for components able generate sound waves and vibrations for haptic feedback.

In a further possible implementation form of the first aspect, the first alternating magnetic force and the second alternating magnetic force are changed simultaneously, by the same magnitude, by manipulating the electrical current in the first coil and in the second coil, such that the first housing arrangement and the second housing arrangement are both displaced a first displacement distance, in opposite directions, in relation to the main magnet, the main magnet being maintained in the equilibrium position between the first suspension means and the second suspension means, facilitating a bidirectional yet spatially efficient magnet actuator.

In a further possible implementation form of the first aspect, only one of the first alternating magnetic force and the second alternating magnetic force is generated and/or changed, the first alternating magnetic force or the second alternating magnetic force being an attractive force or a repulsive force, the first housing arrangement being displaced a first displacement distance in relation to the main magnet by manipulating the electrical current in the first coil or the second housing arrangement being displaced a first displacement distance in relation to the main magnet by manipulating the electrical current in the second coil, facilitating a magnet actuator which generates vibrations in only one chosen direction.

In a further possible implementation form of the first aspect, the first alternating magnetic force and the second alternating magnetic force are generated simultaneously, the first alternating magnetic force being an attractive force and the second alternating magnetic force being a repulsive force, or the first alternating magnetic force being a repulsive force and the second alternating magnetic force being an attractive force, facilitating application of a second functionality by means of movement of the main magnet, such as generating vibrations within the lower resonance frequency interval, producing e.g. haptic feedback.

In a further possible implementation form of the first aspect, wherein the first alternating magnetic force and the second alternating magnetic force are changed simultaneously, by the same magnitude, by manipulating the electrical current in the first coil and in the second coil, such that the main magnet is displaced a second displacement distance, in relation to the first housing arrangement and the second housing arrangement, the first housing arrangement and the second housing arrangement being maintained in equilibrium positions in the magnet actuator, facilitating a magnet actuator which generates vibrations without affecting the outer dimensions of the magnet actuator.

In a further possible implementation form of the first aspect, only one of the first alternating magnetic force and the second alternating magnetic force is generated and/or changed, the first alternating magnetic force or the second alternating magnetic force being an attractive force or a repulsive force, the main magnet being displaced a second displacement distance in relation to the first housing arrangement and the second housing arrangement by manipulating the electrical current in the first coil, or the main magnet being displaced a second displacement distance in relation to the first housing

arrangement and the second housing arrangement by manipulating the electrical current in the second coil, facilitating a magnet actuator which generates vibrations in only one chosen direction. In a further possible implementation form of the first aspect, displacement by the first displacement distance and displacement by the second displacement distance is executed simultaneously, facilitating generation of vibrations within the lower resonance frequency interval and the higher resonance frequency interval at the same time.

In a further possible implementation form of the first aspect, displacement by the first displacement distance is executed at a first resonance frequency, displacement by the second displacement distance is executed at a second resonance frequency, the first resonance frequency being at least 3 times higher than the second resonance frequency, facilitating e.g. generation of sound waves and haptic feedback at the same time.

In a further possible implementation form of the first aspect, the first suspension means is at least partially compressed in response to displacement between the first housing arrangement and the main magnet, and/or the second suspension means is at least partially compressed in response to displacement between the second housing

arrangement and the main magnet, providing support for the components as well as facilitating transmission of vibrations within the lower resonance frequency range.

In a further possible implementation form of the first aspect, the first coil and the first balancing magnet are arranged between an inner surface of the first housing and the first suspension means, and the second coil and the second balancing magnet are arranged between an inner surface of the second housing and the second suspension means, the main magnet being at least partially enclosed by the first housing and the second housing, which is a simple yet reliable construction which provides sufficient protection for the different components as well as efficiently limits the magnetic fields to the cavity formed by the first housing and the second housing.

In a further possible implementation form of the first aspect, the first housing and the second housing limit the magnetic forces to an enclosed space within at least one of the first housing and the second housing, preventing the magnetic fields from interfering with other objects. According to a second aspect, there is an electronic device comprising a movable surface, a cover, a device chassis enclosed by the moveable surface and the cover, and a magnet actuator according to the above arranged between the movable surface and the device chassis and/or the cover, the magnet actuator being configured to displace the movable surface relative to the device chassis and/or the cover in response to displacement between the main magnet and the first housing arrangement, and/or in response to displacement between the main magnet and the second housing arrangement, of the magnet actuator.

By providing an electronic device with a magnet actuator which is balanced from the start, the other components of the electronic device remain unaffected by, e.g., variations in force or dimensions within the magnet actuator. Such a solution reduces the number of defective electronic devices and hence manufacturing and repair costs. Furthermore, this solution facilitates a very stable magnet actuator which can withstand large external forces.

In a possible implementation form of the second aspect, the first housing of the magnet actuator is attached to the movable surface, and the second housing of the magnet actuator is attached to the device chassis or the cover, and wherein displacement of the movable surface generates vibrations having a first resonance frequency within the electronic device, facilitating production of e.g. sound waves.

In a further possible implementation form of the second aspect, the magnet actuator is configured to displace the main magnet relative to the movable surface, the device chassis, and/or the cover, and wherein displacement of the main magnet generates vibrations having a second resonance frequency within the electronic device, facilitating production of e.g. haptic feedback. In a further possible implementation form of the second aspect, the movable surface is a display, facilitating the production of vibrations without needing additional, separate components.

This and other aspects will be apparent from the embodiments described below.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following detailed portion of the present disclosure, the aspects, embodiments and implementations will be explained in more detail with reference to the example embodiments shown in the drawings, in which:

Fig. 1 shows a schematic cross-sectional side view of an electronic device in accordance with one embodiment of the present invention;

Fig. 2 shows a partial, cross-sectional side view of a magnet actuator in accordance with one embodiment of the present invention;

Fig. 3 shows a partial exploded view of the magnet actuator shown in Fig. 2;

Fig. 4a shows a partial, cross-sectional side view of an embodiment of the magnet actuator, in an equilibrium state;

Fig. 4b shows a partial, cross-sectional side view of an electronic device comprising the magnet actuator shown in Fig. 4a, the magnet actuator being in a non-equilibrium state;

Fig. 5a shows a partial, cross-sectional side view of an embodiment of the magnet actuator, in an equilibrium state; Fig. 5b shows a partial, cross-sectional side view of an electronic device comprising the magnet actuator shown in Fig. 5a, the magnet actuator being in a non-equilibrium state;

Fig. 6a shows a partial, cross-sectional side view of an embodiment of the magnet actuator, in an equilibrium state;

Fig. 6b shows a partial, cross-sectional side view of an electronic device comprising the magnet actuator shown in Fig. 6a, the magnet actuator being in a non-equilibrium state;

Fig. 7a shows a partial, cross-sectional side view of an embodiment of the magnet actuator, in an equilibrium state;

Fig. 7b shows a partial, cross-sectional side view of an electronic device comprising the magnet actuator shown in Fig. 7a, the magnet actuator being in a a non-equilibrium state;

DETAILED DESCRIPTION

Fig. 2 shows an embodiment of a magnet actuator 1 in accordance with the present disclosure, and Fig. 1 shows an embodiment of an electronic device 5, in accordance with the present disclosure, comprising the magnet actuator 1.

The magnet actuator 1 comprises a first housing arrangement 2, a second housing arrangement 3, and a main magnet 4 arranged essentially between the first housing arrangement 2 and the second housing arrangement 3.

The first housing arrangement 2 comprises a first housing 2a, a first balancing magnet 2b, a first coil 2c partially surrounding the first balancing magnet 2b as shown in Fig. 3, and a first suspension means 2d. The second housing arrangement 3 comprises a second housing 3a, a second balancing magnet 3b, a second coil 3c partially surrounding the second balancing magnet 3b as shown in Fig. 3, and a second suspension means 3d. The first housing 2a and the second housing 3a are made of magnetic material, such as steel. Furthermore, the housings 2a, 3a may both be shaped as a hollow cylinder having one closed end and one open end, i.e. the cross-section of each housing 2a, 3a, along its center axis, which corresponds to the center axis of the magnet actuator 1, is essentially U-shaped. The peripheral surface of each housing 2a, 3a could have circular or elliptical shape, or e.g. be a polygon.

The open end of the first housing 2a and the open end of the second housing 3a are arranged such that they face each other, allowing the magnet to be at least partially enclosed by the first housing 2a and the second housing 3a. This allows the first housing 2a and the second housing 3a to limit any magnetic forces generated by the magnet actuator 1 to an enclosed space within at least one of the first housing 2a and the second housing 3a.

The first balancing magnet 2b, the first coil 2c, and the first suspension means 2d are at least partially surrounded by the first housing 2a. The first coil 2c and the first balancing magnet 2b are arranged between an inner surface of the first housing 2a and the first suspension means 2d, and preferably fixed to the first housing 2a by means of adhesive. Correspondingly, the second balancing magnet 3b, the second coil 3c, and the second suspension means 3d are at least partially surrounded by the second housing 3a. The second coil 3c and the second balancing magnet 3b are arranged between an inner surface of the second housing 3a and the second suspension means 3d, and preferably fixed to the second housing 3a by means of adhesive. The first suspension means 2d and the second suspension means 3d may comprise of a spring or a soft suspension material layer with low stiffness. The first coil 2c and the second coil 3d may be planar voice coils, and connected to audio amplifiers.

The main magnet 4 is arranged between the first suspension means 2d of the first housing arrangement 2 and the second suspension means 3d of the second housing arrangement 3. The main magnet 4 is fixedly connected to the second suspension means 3d, while being completely disconnected from the first suspension means 2d, allowing the main magnet 4 to float between the suspension means 2d, 3d. The main magnet 4 may be in abutment to the first suspension means 2d or separated from the first suspension means 2d by means of an air gap.

During actuation of the magnet actuator 1, the first suspension means 2d may be at least partially compressed in response to displacement D between the first housing

arrangement 2 and the main magnet 4, and/or the second suspension means 3d may be at least partially compressed in response to displacement D between the second housing arrangement 3 and the main magnet 4. Fig. 5b shows an embodiment wherein the first suspension means 2d and the second suspension means 3d have both been compressed. Fig. 4b shows an embodiment wherein the first suspension means 2d and the second suspension means 3d have both been expanded. Fig. 6b shows an embodiment wherein the first suspension means 2d has been expanded and the second suspension means 3d has been compressed. Fig. 7b shows an embodiment wherein the first suspension means 2d has been compressed and the second suspension means 3d has been expanded.

As shown in Fig. 3, a first constant attractive force Fcl is generated between the first housing 2a and the main magnet 4. The first balancing magnet 2b and the main magnet 4 are configured to generate a first constant repulsive force Fc2 counteracting the first constant attractive force Fcl, such that the first housing arrangement 2 and the main magnet 4 are maintained in a force equilibrium state. Correspondingly, a second constant repulsive force Fc3 is generated between the second housing 3a and the main magnet 4. The second balancing magnet 3b and the main magnet 4 are configured to generate a second constant attractive force Fc4 counteracting the second constant repulsive force Fc3, such that the second housing arrangement 3 and the main magnet 4 are maintained in a force equilibrium state.

As shown in Figs. 4-7, the first coil 2c and the main magnet 4 are configured to generate a first alternating magnetic force F _A I , while the second coil 3c and the main magnet 4 are configured to generate a second alternating magnetic force F _A 2. By manipulating the electrical current in the first coil 2c, a change in the first alternating magnetic force F _A I is caused, which in turn causes a displacement D between the first housing arrangement 2 and the main magnet 4. The displacement D may comprise of the first housing

arrangement 2 being moved in relation to a stationary main magnet 4, or the main magnet 4 may be moved in relation to a stationary first housing arrangement 2. By manipulating electrical current in the second coil 3c, a change in the second alternating magnetic force F _A 2 is caused, which in turn causes a displacement D between the second housing arrangement 3 and the main magnet 4. The displacement D may comprise of the second housing arrangement 3 being moved in relation to a stationary main magnet 4, or the main magnet 4 may be moved in relation to a stationary second housing arrangement 3.

The first alternating magnetic force F _A I and the second alternating magnetic force F _A 2 are one of an attractive force and a repulsive force, the first alternating magnetic force F _A I and the second alternating magnetic force F _A 2 being generated and/or changed independently or simultaneously.

In some embodiments, i.e. shown in Figs. 4a to 5b, the first alternating magnetic force F _A I and the second alternating magnetic force F _A 2 are generated simultaneously. The first alternating magnetic force F _A I and the second alternating magnetic force F _A 2 are both attractive forces or repulsive forces, allowing the main magnet 4 to be maintained in an equilibrium position between the first suspension means 2d and the second suspension means 3d.

The first alternating magnetic force F _A I and the second alternating magnetic force F _A 2 may also be changed simultaneously, by the same magnitude, by manipulating the electrical current in the first coil 2c and in the second coil 3c. As shown in Figs. 4b and 5b, the first housing arrangement 2 and the second housing arrangement 3 are both displaced a first displacement distance dl, but in opposite directions, in relation to the main magnet 4. This allows the height of the magnet actuator 1 to vary in accordance with the AC drive signal, while the main magnet 4 is maintained in the equilibrium position between the first suspension means 2d and the second suspension means 3d. The first coil 2c and the second coil 3c are driven with reversed electrical phase. With a positive phase signal, the first alternating magnetic force F _A I and the second alternating magnetic force F _A 2 are both repulsive forces, forcing the first housing arrangement 2 and the second housing arrangement 3 in opposite directions away from one another and increasing the height of the magnet actuator 1. With a negative phase signal, the first alternating magnetic force F _A I and the second alternating magnetic force F _A 2 are both attractive forces, forcing the first housing arrangement 2 and the second housing arrangement 3 in opposite directions towards one another and decreasing the height of the magnet actuator 1.

The first alternating magnetic force F _A I and the second alternating magnetic force F _A 2 may be changed simultaneously, by different magnitudes, by manipulating the electrical current in the first coil 2c and in the second coil 3c, such that the first housing arrangement 2 and the second housing arrangement 3 are displaced at different resonance frequencies.

In one embodiment, only one of the first alternating magnetic force F _A I and the second alternating magnetic force F _A 2 is generated and/or changed. The first alternating magnetic force F _A I or the second alternating magnetic force F _A 2 is either an attractive force or a repulsive force. The first housing arrangement 2 may be displaced a first displacement distance dl in relation to the main magnet 4 by manipulating the electrical current in the first coil 2c. Optionally, the second housing arrangement 3 is displaced a first displacement distance dl in relation to the main magnet by manipulating the electrical current in the second coil 3c.

In one embodiment, as shown in Figs. 6b and 7b, the first alternating magnetic force F _A I and the second alternating magnetic force F _A 2 are generated simultaneously, the first alternating magnetic force F _A I being an attractive force and the second alternating magnetic force F _A 2 being a repulsive force, or optionally, the first alternating magnetic force F _A I being a repulsive force and the second alternating magnetic force F _A 2 being an attractive force. The first coil 2c and the second coil 3c are driven with the same electrical phase. The first alternating magnetic force F _A I and the second alternating magnetic force F _A 2 force the main magnet 4 in the same direction, away from one of the first housing arrangement 2 and the second housing arrangement 3, and towards the other of the second housing arrangement 3 and the first housing arrangement 2. The original height of the magnet actuator 1 is maintained, I part due to the structure into which the magnet actuator 1 is mounted.

The first alternating magnetic force F _A I and the second alternating magnetic force F _A 2 may be changed simultaneously, by the same magnitude, by manipulating the electrical current in the first coil 2c and in the second coil 3c. This allows the main magnet 4 to be displaced a second displacement distance d2, in relation to the first housing arrangement 2 and the second housing arrangement 3, the first housing arrangement and the second housing arrangement 3 being maintained in equilibrium positions in the magnet actuator 1.

In one embodiment, only one of the first alternating magnetic force F _A I and the second alternating magnetic force F _A 2 is generated and/or changed, the first alternating magnetic force F _A I or the second alternating magnetic force F _A 2 being an attractive force or a repulsive force. This allows the main magnet 4 to be displaced a second displacement distance d2 in relation to the first housing arrangement 2 and the second housing arrangement 3 by manipulating the electrical current in the first coil 2c, or

the main magnet 4 to be displaced a second displacement distance d2 in relation to the first housing arrangement 2 and the second housing arrangement 3 by manipulating the electrical current in the second coil 3c.

In one embodiment, displacement D by the first displacement distance dl is executed at a first resonance frequency, within a first resonance frequency interval, while displacement D by the second displacement distance d2 is executed at a second resonance frequency, within a second resonance frequency interval. The first resonance frequency is at least 3 times higher than the second resonance frequency, e.g. the first resonance frequency may be ca 1000 Hz while the second resonance frequency is ca 100 Hz. The lower second resonance frequency is facilitated due to the low stiffness of the suspension means, which allows enough movement of the main magnet 4 to generate vibrations having the second resonance frequency, while not affecting the position of the first housing arrangement 2 and the second housing arrangement 3. The first resonance frequency interval is generally suitable for producing vibrations in the form of sound waves, and the second resonance frequency interval is suitable for producing vibrations in the form of haptic feedback to the user. The second resonance frequency interval may also be suitable for use as a subwoofer, expanding the audio band to frequencies too low to be comprised within the first resonance frequency interval.

Displacement D by the first displacement distance dl at a first resonance frequency, and displacement D by the second displacement distance d2 at a second resonance frequency may be executed simultaneously, i.e. sound waves and haptic feedback may be generated simultaneously or individually. In one embodiment, privacy leakage is minimized by allowing sound waves to be produced by means of vibrations at first resonance frequency, in one direction, while the vibration coupling in the opposite direction, e.g. to the back cover of an electronic device comprising the magnet actuator 1, is minimized by simultaneously allowing vibrations at second resonance frequency, the second suspension means 3 transmitting vibrations at the second resonance frequency instead of the first resonance frequency.

The present disclosure further relates to an electronic device 5 comprising a movable surface 6, such as a display, a cover 7, a device chassis 8 enclosed by the moveable surface 6 and the cover 7, and a magnet actuator 1, as shown schematically in Fig. 1. The magnet actuator 1 is arranged between the movable surface 6 and the device chassis 8 and/or the cover 7. The device chassis may comprise a printed circuit board (PCB) and the cover 7 may comprise the back cover of the electronic device. The magnet actuator 1 is configured to displace the movable surface 6 relative to the device chassis 8 and/or the cover 7 in response to displacement D between the main magnet 4 and the first housing arrangement 2, and/or in response to displacement D between the main magnet 4 and the second housing arrangement 3, of the magnet actuator 1.

In one embodiment, the first housing 2a of the magnet actuator 1 is attached to the movable surface 6, preferably by means of adhesive, and the second housing 3a of the magnet actuator 1 is attached to the device chassis 8 or the cover 7, preferably by means of adhesive. Due to the stiffness of the moveable surface 6 and the device chassis 8 or the cover 7, the system comprising the moveable surface 6, the device chassis 8 or the cover 7, and the magnet actuator 1 has high spring-mass resonance facilitating high resonance frequencies.

Displacement D of the movable surface 6, by means of the magnet actuator 1, generates vibrations having a first resonance frequency within the electronic device 5. The moveable surface 6 may be displaced such that it bends in a direction from, during positive phase signal, or towards, during negative phase signal, the device chassis 8 or the cover 7.

The magnet actuator 1 may be configured to displace the main magnet 4 relative to the movable surface 6, the device chassis 8, and/or the cover 7. Displacement D of the main magnet 4 generates vibrations having a second resonance frequency within the electronic device 5. The second resonance frequency is facilitated due to the low stiffness of the suspension means, which allows enough movement of the main magnet 4 to generate vibrations having the second resonance frequency, while not being enough to overcome the stiffness of the moveable surface 6 and the device chassis 8 or the cover 7, and subsequently move the first housing arrangement 2 and the second housing arrangement 3.

The various aspects and implementations have been described in conjunction with various embodiments herein. However, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed subject-matter, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word“comprising” does not exclude other elements or steps, and the indefinite article“a” or“an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. The reference signs used in the claims shall not be construed as limiting the scope.