DE3338998C2 - Force transducer - Google Patents

Description

The invention relates to a force transducer according to the preamble of claim 1.

Such a force transducer is already known from DE-OS 03 141. The pressure sensitive device consists of one or two conductor loops, which can also be designed in the form of a coil, whereby a change in inductance or mutual inductance is measured when a force is applied. Using of a conductor loop is the change in inductance by changing the distance of an electrical Screen generated, with two conductor loops, which are preferably arranged at right angles to each other, the Mutual inductance changed by changing the angle between the two conductor loops.

Both measuring principles can only be used to a very limited extent for recording two-dimensional force distributions use because they require a very high circuitry complexity for inductance measurement and, moreover, a simple matrix-type control and query is not possible.

Likewise, a similar force transducer from DE-OS 30 11 266 is already known. The transducer elements are formed here by crossed electrically conductive strips, at their crossing points a force-proportional electrical resistance is measured through an electrically conductive material. Disadvantage:

- poor mechanical decoupling of neighboring transducer elements,

- inhomogeneous age-related changes in resistance of the conductive elastic material,

high electrical interference at high query speeds,

insufficient flexibility due to the conductive contact strips,
low sensitivity,
Electrical resistance hysteresis.

The object of the invention is to develop a force transducer according to the preamble of claim 1 in such a way that that a mechanical decoupling of the transducer elements takes place, no signs of aging occur, that great flexibility of the mat can be achieved, that the electrical values of the transducer elements are low Have tolerances, that the sensitivity can be selected over a wide range, that very high query speeds possible are.

This object is achieved by the measures in the characterizing part of claim 1. Further developments are described in the subclaims.

The invention is explained in more detail below with reference to the drawings
1 shows a schematic structure of a transducer element, FIG. 2 section through a transducer element,
Fig. 3 Interconnection in the form of a measuring mat with control and evaluation electronics.

F i g. 1 and 2 show the newly developed force transducer. This provides the electrotechnical basics Transformer principle: a primary inductance through which an alternating current of constant amplitude flows (11,21) induced due to the magnetic coupling in a secondary inductance (12, 22) a voltage whose amplitude at constant electrophysical Values (self-inductance) mainly depends on the degree of coupling Represent air coils as a function of the distance between the two coils.

The primary and secondary inductance (11, 21, 12, 22) are, for example, spirals etched onto epoxy plates (24) with 19 turns each (thickness: 0.3 mm, Z = 10 mm), the connections of which are led out diagonally. The force / path transforming element (13, 23) that changes the coupling factor is a special foam (thickness: 1 mm), the spring characteristic of which has been determined experimentally.

If a force F acts on one of the two coils, their distance from one another is reduced. The resulting increase in amplitude of the induced secondary voltage is *, a measure of the force applied, is not linear, but rather approaches an end value asymptotically.

The transfer function of the force transducer is largely due to the self-inductances and the geometric arrangement of the two coils to each other determined. Both factors can be used in the coil and optimize mat production in such a way that very low exchange tolerances are achieved with high measurement accuracy will.

The measuring range of the force transducer is determined by the compressibility of the spring element. It can be determined in the range of 0.4 N / cm ² ... 150 N / cm ² .

The force transducers can be arranged in a matrix with any number of columns and rows in a measuring mat by connecting the primary or secondary coils in series to be ordered. The center distance is determined from the diameter of the coils and their Arrangement to each other. Wiring and converter are covered with fiberglass up to the height of the spring element.

cast in reinforced silicone rubber and thus largely protected against mechanical damage with sufficient flexibility. Measuring mats of any shape can be produced using this process.

F i g. 3 shows the basic electronic structure of the laboratory measuring system.

The process computer controls the row and column switches, via which each force transducer is interrogated briefly (50 | is) once during a measuring cycle: when a constant current (f = 1 MHz) is impressed on a (primary) column, a (secondary) -) Line measured the voltage induced at the intersection of the line / column. This type of matrix-like series connection of primary or secondary coils in conjunction with the above connection sequence ensures complete decoupling of the individual measuring points. After amplification and rectification, the measurement signal is digitized in a fast A / D converter (30 μ5) and stored in the processor. The duration of a measuring cycle is determined by the number of force sensors and is, for example, with a measuring mat with (iö χ 20) sensors 200 100 us = 20 ms.

1 sheet of drawings

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Claims (5)

Patent claims: 1. Force transducer in the form of a flexible measuring mat, especially for measurement and registration of areal pressure distributions, with several transducer elements with relatively small dimensions are interconnected in a measuring mat, characterized in that a transducer element consists of two flat or planar coils (11,12,21,22) facing each other at a distance, which through an elastic plastic (13,23) are mechanically connected to one another, with by imprinting an alternating current of constant amplitude through the primary coil (11, 21) due to the magnetic Coupling in the secondary coil (12, 22) induces a voltage proportional to the force. 2. Converter according to claim 1, characterized in that several coils (11,21 or 12,22) in Rows connected at right angles to each other (rows or columns) are, and each crossing point represents a wall element 3. Converter according to claim 1, characterized in that the coils (11, 12, 21, 22) photolithographically are applied to plastic plate (24), and that the elastic plastic (13, 23) Foam is made. 4. Converter according to claim 3, characterized in that the plastic plate (24) is flexible are. 5. Converter according to claim 3, characterized in that the elastic plastic (13, 23) Ferrite material is added.