CONTACT DEVICE FOR DELIVERING ELECTRICAL SIGNALS CORRESPONDING TO THE POSITION OF A MOVABLE BODY

Abstract: A contact device for delivering electrical signals corresponding to the position of a movable body comprises a base layer (10) and a flexible layer (11), which is positioned in front of the base layer and spaced from the base layer. One layer (for example 10) is provided with a first elongated electrical conductor (15) and the other layer (11) is provided with at least one contact element (19), which is so arranged that at least a portion of the contact element is positioned in front of a portion of the first conductor (15). A pressure means (21) connected to the movable body is arranged to abut against the flexible layer (11) and to be moved on the flexible layer, when the movable body is moved. A second elongated electrical conductor (18) is in electrical contact with the contact element (19), so that an electrically conducting path is formed between the first conductor (15) and the second conductor (18) through the contact element (19), when the flexible layer is forced against the base layer when the pressure means passes the contact element. The contact device has a small size and can easily be adapted to different components and fields of application.

Description: Contact device for delivering electrical signals corresponding to the position of a movable body Technical Field The present invention relates to a contact device for delivering electrical signals corresponding to the position of a movable body. The contact device is primarily intended for use in position indicators and angle indicators but can also well be used in other types of indicators, where it is desirable to produce electrical signals corresponding to the position of a movable body. Background Art It is previously known to use contact devices to produce electrical signals corresponding to the movement of a ' body, for example in revolution counters for motors or in angle position indicators for bodies rotating or turning around a sha . The contact devices at present in use for this purpose comprise a large number of separate, movable contact means and therefore take up a comparatively great deal of space. They are also comparatively heavy and expensive to manufacture and assemble. Disclosure of Invention The main object of the invention is to provide a contact device which requires a very small space, which has a very low weight and which is inexpensive to manufacture and, furthermore-, easily can be adapted to different components and fields of application. This object is achieved according to the invention by giving the contact device the features set forth in the claims. The contact device is characterized by the fact that it comprises a base layer and a flexible layer, the layers being provided with electrical conductors and contact elements which gradually can be brought into electrical contact with each other by pushing the flexible layer against the base layer by means of a pressure element movable over the surface of the flexible layer. Due to the fact that the layers and the electrical conductors can be made very thin, the contact means will require only a very small space. Furthermore, the contact means has a very low weight and is easy to manufacture. Due to the fact that the shapes of the layers and the conductors can be varied, the contact device can easily be adapted to different components and fields of application. Brief Description of Drawings One embodiment of the invention will now be further described below with reference to the accompanying drawings. Figure 1 is a schematical view of one embodiment of a contact device according to the invention which is designed for producing pulses in a rotating motor for counting the number of revolutions and/or for indicating the angle position of the motor shaft. Figure 2 is a schematical cross section view through the contact device according to Figure 1 along the line II-II. Best Mode for Carrying Out the Invention The contact device shown in Figs. 1 and 2 comprises a base layer 10 and a flexible layer 11. The flexible layer 11 is positioned in front of the base layer and is spaced from the base layer by means of two spacing elements 12,13. The base layer has a circular shape with a central hole 14 and is provided with two elongated electrical conductors 15,16 on the side facing the flexible layer. The electrical conductors are positioned between the spacing elements and form concentric circular rings around the central hole 14. The outer diameter of the inner ring is substantially smaller than the inner diameter of the outer ring, so that a space 17 is formed between the conductors 15 and 16. The flexible layer 11 has a central hole corresponding to the central hole 14 of the base layer and is provided with an elongated electrical conductor 18 on the side facing the base layer. The electrical conductor 18 forms a circular ring which is concentric with the conductors 15,16. The inner diameter of the conductor 18 is larger than the outer diameter of the conductor 15, and the outer diameter of the conductor 18 is smaller than the inner diameter of the conductor 16. The conductor 18 is positioned straight over the space 17 between the conductors 15 " ,16, so that the conductor 18 can be placed in the space 17 between the conductors 15,16 without touching the conductors 15,16, when the layer 11 is pushed down. The conductor 18 is provided with a large number of tabs 19,20 projecting perpendicularly to the longitudinal direction of the conductor, i.e. radially with regard to the circular ring formed by the conductor. The tabs 19,20 have a length such that they at least partially overlap the conductors 15,16 provided on the base layer. Thus, when the flexible layer 11 is pushed down, the tabs 19 projecting radially inwards will come into contact with the inner conductor 15 and the tabs 20 projecting radially outwards will come into contact with the outer conductor 16 on the base layer. The tabs 19,20 are positioned radially in front of each other. The conductors 15,16 and 18 are connected to connectors 15A,16A and 18A provided on a strip 10A projecting from the base layer. The connectors 15A,16A and 18A are insulated from each other and from the other conductors and at their ends provided with terminals 15B,16B and 18B. The base layer 10 and the flexible layer 11 may be very thin layers, for example of plastic foils, and the conductors 15,16,18 and their connectors may be thin metal layers. Because the distance between the conductors 15,16 on one side and the tabs 19,20 of the conductor 18 on the other side only has to be so large that an electrical contact between the conductors is prevented, when the flexible layer is not pushed down, the complete contact device can have a very low height. Thus, the required space for the height is very small, even with regard to the pressure element 21 schematically indicated with broken lines in Fig.2 and required for pushing down the flexible layer 11, as will be more clearly explained below. The contact device shown in Figs. 1 and 2 is designed to be applied to an electric motor for counting the number of revolutions and portions of a revolution that the motor shaft has turned from a starting position, for example. The contact device is then attached to one end surface of the motor in a plane which is perpendicular to the motor shaft. The motor shaft is provided with an arm or disc rotating with the motor shaft and provided with a pressure element abutting against the flexible layer of the contact device. The pressure element is adapted to slide over the conductor 18 and its projecting tabs 19,20, which act as contact elements, and gradually force the tabs into contact with the conductors 15,16 on the base layer, when the motor rotates. The terminal 18B of the conductor 18 is connected to a voltage supply and a pulse is then obtained on the terminals 15B and 16B each time the pertaining conductors 15 and 16, respectively, come into contact with a projecting tab on the conductor 18. The number of received pulses is a direct indication of the number of revolutions and portions of a revolution that the motor shaft has turned. When the pressure element 21 slides over the conductor 18 and its projecting tabs 19,20, the flexible layer 11 is pushed down under the pressure element, so that the portion of the conductor 18 lying under the pressure element is forced against the base layer. In the areas where no projecting tabs are present, the conductor 18 will be pushed down into the space 17 between the conductors 15,16 without contacting any of the conductors 15,16. However, each time the pressure element passes over projecting tabs on the conductor 18, these tabs and thus also the conductor 18 will be brought into contact with the conductors 15,16. Thus, for each revolution of the motor shaft the tabs 19,20 of the conductor 18 will gradually come into contact with the conductors 15 and 16, respectively, so that pulses are transmitted over the terminals 15B and 16B, respectively. While only one embodiment of the contact device according to the invention has been illustrated and described above, it is obvious that many modifications and variations are possible within the scope of the invention. For example, the electric conductors can run substantially in a straight line or along any curve, and the contact device can then be used as position indicator for bodies or elements movable from one point to another, for example in motor vehicles to indicate the position of movable chairs; in connection with locking means in automatic seat belt systems, and in height adjusters for safety belts. Furthermore, it is not necessary to use more than two electrical conductors for providing output pulses. In that case, either both conductors can be applied on the same layer, for example the flexible layer, the base layer then being provided only with contact elements crossing the conductors and the conductors being forced against said crossing elements, when the pressure element is moved over the flexible layer, or one conductor can be applied on one layer and the other conductor can be applied on the other layer, one of said conductors being provided with projecting tongues or tabs which form contact elements and which are brought into contact with the other conductor, when the pressure element is moved over the flexible layer. However, the provision of three conductors give many possibilities of further improvements and more advanced control of the movement of a body between two points. The use of two parallel conductors for the output pulses shown in the disclosed embodiment provides a higher reliabilty in the pulse count. If the inwards and outwards projecting tabs are displaced with regard to each other, so that the tabs are not positioned on the same radius, two different series of pulses are obtained which can be used to achieve a higher accuracy in determining a position, for example when the contact device is used for determining an angle, and for determining the direction of rotation. Alternatively, a higher number of tabs can be provided on one output conductor and the tabs can be positioned with different spaces, so that the pulses of the pertaining series of pulses can be used for speed control of the movable body, for example so that a higher number of pulses per time unit will give an acceleration of the body on straight paths and a lower number of pulses will give a retardation, for example just oefore a home position, or for indication of an angle by means of a code, for example a Gray-code. Furthermore, one output conductor may consist of a resistive layer, so that the resistance of the conductor depends upon the position of the pressure element. This will provide a possibility to perform a digital as well as an analog signal output. Alternatively, one conductor can be designed as a resistive temperature sensor, making the contact device self-adjusting, so that the accuracy in indication of a position or an angle is increased, when the temperature changes heavily. The base layer may be flexible or rigid and possibly consist of a surface on the component to which the contact device is to be attached. The conductors and contact elements required on the base layer are then applied directly on the surface of the component. Due to the fact that the contact device comprises a flexible layer on which one or more conductors and/or one or more conta ' ct elements are provided, the contact device may be completely sealed which increases the service life of the device and reduces the risk of contact trouble, particularly in dirty environments, for example in motor vehicles. Due to the fact that the conductors can have any shape, the contact device is easy to adapt for the intended field of appli¬ cation. The small space required makes a contact device according to the invention easy to insert into units already manufactured, for example finished motors.

Claims: C laims 1. Contact device for delivering electrical signals corresponding to the position of a movable body, characterized in that it comprises a base layer (10) and a flexible layer (11), which is positioned in front of the base 5 layer and spaced from the base layer, one layer (for example 10) being provided with a first elongated electrical conductor (15) and the other layer (11) being provided with at least one contact element (19), which is so arranged that at least a portion of the contact element is positioned in 10 front of a portion of the first conductor (15); a pressure means (21) connected to the movable body and arranged to abut against the flexible layer (11) and to be moved on the flexible layer, when the movable body is moved, substantially along the path of the first conductor (15), so that an 15 electrical contact is provided between the first conductor (15) and the contact element (19), when the pressure means (21) passes the contact element; and a second elongated electrical conductor (18), which is arranged to be in electrical contact with the contact element (19), when the 20 pressure means passes the contact element, so that an electrically conducting path is formed between the first conductor (15) and the second conductor (18) through the contact element (19), when the flexible layer is forced against the base layer when the pressure means passes the 25 contact element. 2. Contact device according to claim 1, characterized in that the first conductor and the second conductor are provided on the same layer, the contact element being provided on the other layer. 303. Contact device according to claim 1, characterized in that the first conductor (15) is provided on one layer (10) and the other conductor (18) and the contact element (19) are provided on the other layer (11). 4. Contact device according to claim 3, characterized in that the contact element (19) is connected to the other conductor (18) by means of a fixed connection. 5. Contact device according to any of claims 2-4, characterized in that several contact elements (19) are provided, at least a portion of each contact element being positioned in front of the first conductor (15), so that an electrical contact is provided between the first conductor (15) and each contact element (19) in turn, when the pressure means (21) is moved along the path of the first conductor. 6. Contact device according to claim 5, characterized in that the contact elements are positioned with different spaces between them. 7. Contact device according to any of claims 1-6, characterized in that the first conductor and the second conductor are positioned along a substantially linear path. 8. Contact device according to any of claims 1-6, characterized in that the first conductor and the second conductor (15,18) are positioned along substantially concentric, circular paths. 9. Contact device according to any of the preceding claims, characterized in that a third electrical conductor (16) is positioned beside the first conductor (15) and that at least one contact element (20) is arranged to provide an electrical contact between the third conductor (16) and at least one of the two other conductors (15,18), when the pressure means (21) passes the contact element. 10. Contact device according to any of the preceding claims, characterized in that the contact elements (19,20) consist of thin strips positioned substantailly perpendicularly to the longitudinal direction of the conductors (15,16,18). 11. Contact device according to claims 8 and 10, particularly for indication of the position of bodies rotating around a shaft, characterized in that it comprises a first layer (10) having two electrical conductors (15,16) which are shaped as concentric, circular rings with different radii and form an intermediate circular space (17), and a flexible layer (11) having an electrical conductor (18) which is shaped as a circular ring and which is positioned in front of the space (17) between the circular conductors (15,16) on the first layer (10) and provided with radially tabs (19,20) projecting inwards as well as outwards and overlapping the conductors (15,16) of the first layer.

Inventors: HAWRANEK JERZY, HAWRANEK, JERZY
Applicants: AUTOLIV DEV, AUTOLIV DEVELOPMENT AKTIEBOLAG
Application year: 1987
Main classification: G01B7
IPC codes: G01B7, G01D5