GB2191005A - Inductive proximity switch - Google Patents

Description

GB2191005A SPECIFICATION in stylized form (Figs la and b) with an active

surface a emits an alternating field in the case

An inductive proximity switch of frontal or lateral approach of a damping body B (Fig la) to the drawn-in switching dis The present invention relates to an inductive 70 tances (points) of the symmetrical curves of proximity switch, and to a method of operat- the switching distances S1 and S2 emits a ing an inductive proximity switch. switching function. In the case of a pot core A known inductive proximity switch generconstruction the curves of the switching dis ally comprises an oscillator part, a signal tances S 1, S2 are to be looked upon as longi evaluation or processing part and a (generally 75 tudinal sections of envelope surfaces of the short-circuit-proof) output or final stage. The loci of all possible switching distances, a switching characteristic of such a switch is a switching function occuring when penetrated function of the oscillator field and has a very with an e.g. metallic damping body. This en specific geometrical spread with respect to velope surface as a locus of all the switching the active surface of the proximity switch. In 80 distances of an oscillator coil can, when con the simplest case, when there is an oscillator sidered infinitesimally, be penetrated by a coil in a pot core, symmetrical conditions ap- damping body from any direction, other than ply, so that the parameter group of different through the active surface a. However, in gen switching characteristics consists of a set of eral only lateral and frontal approaches are envelope curves of a functional configuration. 85 used.

In accordance with the approximation or ap- The oscillator for operation according to the proach path of a damping body in the field invention has, as a result of a simultaneous range of the oscillator, there is a specific en- evaluation of the oscillator output character velope curve with the loci of the switching istics shown in Fig 2, as a function of the distances, spacings or intervals. 90 distance of damping portion B from a remote The object of the invention is to provide an and a near point, two envelope curves in one improved inductive proximity switch. another and which, when penetrated by a According to the invention this object is damping body, bring about the successive achieved in that an oscillator is so dimen- generation of a switching signal. This is repre sioned that its output characteristic is ex- 95 sented in fig la by the sectional representa tended, so that over the entire possible range tion of the two envelope surfaces of switching switching distances can be defined, which are distances S 1, S2 and in fig 'I b by two switch as far apart as possible. ing ranges of switching distances S1, S2 with In an embodiment of the invention, this can different dispersion or spread (range width) of be achieved with an oscillator having an oscil- 100 approximately 20% for the remote region lator coil, with a centre and end tap and with and approximately 5% for the near region.

a leading out of the analogue oscillator output The two different representations are also signal for providing switching signals with difused for showing the two most frequent ferent switching distances. According to other cases of the approach of a damping body, erndobiments a single switching point or both 105 laterally and frontally with respect to the oscil- switching points can be varied, so as to be lator. Fig la shows the more frequent lateral able to realise random window functions. approach, in which a damping body B moving An embodiment of the invention will now in the direction of the arrow, firstly produces be described by way of example with refer- the switching signal for switching distances ence to the accompanying drawings, in which: 110 S1 and during further advance the switching Fig la is a stylized representation of an os- signal for switching distances S2. The same cillator with a drawn-in configuration of the occurs in the case of frontal approach accord loci of switching distances and a damping ing to fig 'I b when damping body B ap body for lateral approach. proaches the oscillator on path x in the direc Fig lb is another representation of an oscil- 115 tion of the arrow. When considered strictly in lator with associated switching ranges and a fig la mean values from a switching range damping body for frontal approach. with the switching points determining the en Fig 2 is a typical switching function U=f(x) velope curve are shown, said switching range of a switch in stylized representation, and a of switching distances S1 20% and switch damping body; (oscillator-damping body 120 ing distances S2 5%, being shown together pair). with a normal switching distance Sn (mean Fig 3 is a general circuitry example of an values) in fig lb. Here again, a damping body embodiment of the invention. frontally approaching the oscillator will succes Figs 4a to 4c, are different switching func- sively produce two evaluatable signals of the tions of two or three-conductor switches and 125 switching distances S1, S2.

with a four-conductor switch with two out- The realization of the two switching points puts, and can be achieved by simultaneous evaluation of Figs 5a and b are switching functions of the dc signal for the close range and ac signal further embodiments. for the remote range. Thus, without great ex An outwardly open oscillator A represented 130 penditure, is obtained from a conventional in- GB2191005A ductive proximity switch, an inductive two-po- with general wiring or cabling. Apart from the int proximity switch with spatial and/or time feed lines, oscillator 30 has two signal out sequential switching characteristic or, consi- puts A l, A2, one each for the remote region dered in another way, an inductive proximity of switching distances S1 with ac coupled out switch with two ranges is obtained. Such a 70 at A1 and for the close region of the switch novel proximity switch naturally has a wider ing distances S2, where the dc is coupled range of applications than the unchanged, sin- out. In the represented LC oscillator with in gle-point proximity switch. In the case of fron- ductor L and capacitor C, a coil 32 with a tal (and also lateral) approach, one example of centre tap 33 is used. A generally represented this is the early warning possibility, the signal 75 oscillatable driver wiring system 31 of known for the switching distances S1 from the larger type can be used. The two signals of switch range being used for taking preliminary mea- ing distances S 'I and S2 at outputs A 'I and sures prior to reaching the---actualswitching A2 are advantageously simultaneously evalu points emitting the switching signals for ated, i.e. a damping body approaching the os switching distances S2. Such a measure is 80 cillator is perceived by a--- priorzone-, before e.g. the reduction of the speed in order to it reaches the actual switching region. The bring about a more accurate control of the time required by the damping body to pass actual switching point with only an insignifi- from one region into the other can e.g. be cant time loss, because it is only close to the used in order to reduce the speed of the switch or its active surface a. In this case the 85 workpiece or machine part with the damping novel proximity switchacts in the same way body. Apart from this exemplified use, other as a precision proximity switch and specifically usefull applications are conceivable, being when the latter is of an expensive type. made possible for the first time by the pre A functional representation of the above is sent invention.

shown in fig 2 in the form of a graph U=f(x) 90 With a switch according to the invention as superimposed on a stylized oscillator-damp- shown in figs 4a, 4b and 4c, different operat ing body pair. On the distance axis (abscissa) ing modes are possible. The inductive proxim there are three distance (switching voltage) ity switch according to the invention, which ranges for the switching distances S1, Sn, S2 on approaching a damping piece in a first dis- which, according to the representation of fig 95 tance S 'I has the first switching point and in a la, would correspond to three envelope sur- next distance S2 a --- moreexact- second faces. Damping body B approaches the active switching point, can e.g. be realized with the surface a of oscillator A and firstly reaches following specifications:

the vicinity of switching distances S1 with the S 1 is at least 50% greater than Sn accord greatest range and also with the largest ac 100 ing to the CENELEC standard.

portion, as well as the greatest spatial exten- S2 is approximately 50% of Sn sion, i.e. approximately 20%. Towards the S 1 has a precision of 20% over a tem oscillator, there is not only a decrease in the perature range of 25 to 750C ac portion, as shown in the function, but there S2 has a precision of 5% over a temper- is also a change in the function configuration, 105 ature range of 25 to 750C.

passing into a more or less linear zone. The As a 3-conductor switch with two outputs, normal switching function of the switching dis- as shown in fig 3, at output A 1 there is a tances Sn is placed in this zone in the manner switching function according to fig 413 and at known from the operation of inductive proxim- output A2 a switching function according to ity switches. This zone has a switching hys- 110 fig 4A. With respect to switching points S1 teresis of approximately 5 to 20% and corre- and S2, a window function as shown in fig sponds to the normal operation of the proxim- 4C is obtained. Obviously the inverse func ity switch. Even closer to active surface a, tions are possible.

there is an ac-free de zone of switching dis- Measured on the known inductive proximity tances S2 of approximately 5%. This is 115 switches, this window function permits a fur shown by the characteristic switching function ther number of applications and can be varied with the generally not shown ac superimposi- in the manner shown in figs 5A and 5B. A tion in fig 2. first variant is as follows (fig 5A).

It is advantageous to design the oscillator in Switching point S2 is fixed and switching such a way that there is a flat configuration of 120 point S1 is e.g. kept adjustable over a desired function U=f(x), so that the two used zones range by means of a potentiometer. This of the switching distances S1 and S2 (Sn is gives a variable window function for corre not used) are at the greatest possible distance sponding uses.

apart with respect to the abscissa. Thus, the Both switching points S1 and S2 are kept close region of switching distances S2 used 125 variable over a desired range, e.g. by means for switching is spatially remote from the early of a potentiometer. Thus, in the case of fixed warning region of switching distances S1, as window width, a displaceable window function shown in fig 'I a. is obtained and in the case of a variable win Fig 3 is an example of a circuit for the dow width a variable and consequently adjust proximity switch according to the invention 130 able window function for corresponding uses.

3 GB2191005A 3 The adjustment need not be brought about by a potentiometer and constructions are possible in which the window function is automatically adjusted. Thus, a window of ade- quate size in a desired range can be obtained by a regulating process.

Claims (9)

1. An inductive proximity switch comprising an oscillator including. an oscillator coil having a centre tap and an end tap, a first output lead to carry a first switching signal activated in response to the presence of a damping body at a first distance from the switch, and a second output lead to carry a second switching signal activated in response to the presence of a damping body at a second distance from the switch.

2. A switch as claimed in claim 1 in which the first output lead is adapted to carry an A.C. switching signal.

3. A switch as claimed in claim 1 or claim 2 in which the second output lead is adapted to carry a D.C. signal.

4. A switch as claimed in any preceding claim including means to vary the distance from which either or both said switching signals are activated.

5. A method of operating the proximity switch as claimed in claim 1 to provide window functions with the said first and second switching signals.

6. A method as claimed in claim 5, in which said window functions are of variable width.

7. A method as claimed in claim 5 or claim 6, in which said window functions are displaceable.

8. An inauctive proximity switch substantially as herein described and shown in the accompanying drawings.

9. A method of operating an inductive proximity switch substantially as herein described with reference to the accompanying drawings.

Printed for Her Majesty's Stationery Office by Burgess & Son (Abingdon) Ltd, Dd 8991685. 1987Published at The Patent Office, 25 Southampton Buildings, London. WC2A lAY, from which copies may be obtained-