SE519289C2 - Safety device for preventing fingers being trapped in furniture with motor driven components, comprises twin conductor generating capacitive electric field - Google Patents

Abstract

The safety device comprises a twin conductor with two input conductors formed by thin, electrically conducting metal strips lying side by side or symmetrically one above the other. The strips are separated by a thin, insulating dielectric medium. When the motor is activated, the conductors are connected to a weak low voltage alternating current, which flows around, over and along the free sides of the twin conductor to create a symmetrical capacitive alternating current field. The symmetry, capacitance and integrity of this field are locally altered (9) if a body part or finger (8) with an intrinsic capacitance approaches the region (10) where there is a risk of it becoming trapped or comes into direct contact with the twin conductor. This variation is processed using standard electronic techniques, so that the motor is immediately stopped and/or put into reverse. The automatic safety device can be secured to any dangerous surface on the fixed and/or movable sections (7) of the furniture.

Description

25 30 519 289 Sid; The safety devices in these contexts are usually based on the movable mechanical part, which during its motor movement can approach a fixed part of the structure and pose a risk of personal injury, is provided with an electromechanical clamping strip, electrical or pneumatic device, whose signal from touch immediately able to stop and possibly. also reverse the drive motor.

Examples of such safety devices are microswitches which break the current by means of a mechanical core, a low-current electrical arrangement which, when compressed, short-circuits a control circuit or a thin pressure-sensitive hose which is capable of acting on a relay or a switch after some compression.

Common to these safety systems is that a certain amount of compression, and thus a brief shocking experience, is usually required before the safety system releases the drive motor. The clamp protection device according to the invention is intended to release the drive motor even when no part of a person's body part is approached without contact.

CHARACTERISTICS OF THE LJBPFINNINQEN The clamping protection device for motor-driven furniture is based on the fact that as stated in the preamble of the appended claim 1, and is characterized mainly by being designed as a flat, insulated double conductor, connected to a motor, electric motor, motor drive, the double conductor is applied directly to and along the dangerous fixed or moving parts of the equipment in the construction, where clearance risk and personal injury can occur.

The clamp protection device according to the invention is further characterized in that the two electrical conductors of the ambiently insulated double conductor are designed as thin metal strips, preferably of copper, lying with their wide side facing each other, and only separated from each other by a thin insulating layer, constituting a dielectric, and that the flat, superimposed, conductors are always followed with their longitudinal edges exactly coinciding or at different widths, symmetrically through coinciding center lines. A further characteristic of the clamp protection device according to the invention is that the double conductor, already at the start of the engine via the control unit, is supplied with a very weak, low-voltage alternating current, the double conductor radiating along its entire length and each edge radiating. goodness numbers change, even with non-contact approach of a person's body part, and that this signal change is converted in the controller to immediately stop and / or reverse the engine, until the body part is removed and the engine can be started again.

The control device must therefore contain the necessary electrical components to be able to detect a sudden change in the capacitance and goodness number of the dual conductor, and then immediately convert it to break the drive voltage to the motor and / or briefly reverse the direction of rotation of the motor.

The device according to the invention is defined in the appended claims.

The invention will be described in the following in connection with a non-limiting example of its use in a motor-driven hospital bed with an adjustable back section.

The number designations are continuous and consistent in the figures.

Figure 1 shows symbolically and enlarged a cross section of a double conductor (1) in accordance with the invention, with two band-shaped conductors (2) insulated from the environment, separated from each other by a thin insulating dielectric (3), and a double-sided mounting tape (4 ) applied to one wide side of the double conductor.

Figure 2 shows in the same way and with traditionally dashed lines the alternating field (5) which occurs when a weak alternating current with low voltage is connected to the members and the insulated double conductor hangs freely in the air. The gearbox then radiates in an oxygen-uniform and uniform pattern, from edge to edge on the top and bottom of the double conductor and along its entire length. Figure 3 also shows, enlarged, a symbolic cross-sectional view of the double conductor (1) glued with the mounting tape (4) on the surface of a fixed or motor-driven movable construction pipe (6) in, for example, a motor-driven hospital bed with a movable back section. Since one wide side of the double conductor connects tightly to the curved mantle surface of the pipe, the gear field radiates only around the upper side of the double conductor, here clarified with the bar-marked gear field (S).

Figure 4 further symbolically and magnified describes a sequence of events seen in a cross-sectional view, where a movable construction pipe (7) motorically approaches a fixed or stationary construction pipe (6) on which a clamp protection device in the form of the double conductor (1) according to the invention is applied. As soon as the drive motor is activated, the weak alternating current with its low voltage is also connected to the two conductors (2), whereby the double conductor is also activated and radiates its surrounding alternating field, previously described as a symmetrical alternating field (5) in Figure 3.

When a body part or, as here, a finger (8), with its own electrical capacitance, approaches the danger area (10) and the alternating field of the dual conductor, or touches the dual conductor, a local alternating field change occurs, here illustrated as an asymmetric displacement of the alternating field ( 9) against the finger (8). This change can be detected with known technology as an instantaneous change in the capacitance and goodness number of the double conductor (1), and used as a signal from the clamp protection device according to the invention to stop and / or reverse the motor drive immediately, even before full contact. occurred.

Figure 5 shows an example of a structural detail seen from the side, where along a dangerous risk area (10) one must allow two structural pipes (6,7) to also be able to approach each other completely, and connect to each other in parallel. In such a case, the dangerous surfaces of both construction pipes can advantageously be provided with the double conductor (1) according to the design. Where the double members gradually meet each other, the gear field decreases symmetrically and gradually down to completely take each other out, and thus allow parallel contact without ever losing its protective task.

Claims (1)

10 15 25 30 i 519 289 PATENT REQUIREMENTS Page 5 Clamp protection device based on a double conductor (1) isolated from the environment and intended as automatic clamp protection in motorized, person-loaded or unloaded furniture of the type beds, armchairs, patient tables, etc., and mounted (4) against and along all dangerous surfaces on the fixed and / or movable structural parts of the furniture structure (6,7), which when any of these are set in mechanical motion by a drive motor, may constitute an obvious risk of personal injury, characterized in that both conductors (1) of the double conductor (1) are made as very thin electrically conductive metal strips placed wide side to wide side over each other and with their longitudinal edges exactly coincident, alternatively symmetrically coincident along their center lines, and separated from each other by a thin insulating dielectric layer (3) and that, while starting the drive motor, also the two members (2) are connected to a weak low-voltage alternating current to create a constant and symmetrical alternating field (5), s if radiating from both edges and nmt the free side along the entire length of the double conductor (1), and that the smallest measurable change in the capacitance and / or goodness number of the double conductor, caused by a body part or a finger (8) approaching the risk area (10) or touches the dual conductor (1) and thereby causes its gear case (9) to locally deflect and become asymmetrical, is used as a signal to be converted to automatically and immediately stop and / or reverse the drive motor, until the body part is removed from the risk area (10) and drive motor and the clamp protection device can be restarted.