GB2167981A - Adjustable potentiometers - Google Patents

Abstract

Improvements in the manufacture of adjustable potentiometers and to the potentiometers so manufactured, characterised in that the housing body of insulating material which is the component enclosing and protecting the resistive element, the collector, the cursor or wiper 29 and the cursor support 31 is formed in a moulding operation which is combined with the advance of a previously die-stamped metal strip (1, Fig 1) having blanked out spaces which determine the form of the future collector and the external connection terminals 5, 10. The housing body and metal strip form an integral inseparable assembly. <IMAGE>

Description

SPECIFICATION Improvements in the manufacture of adjustable potentiometers and to the potentiometers so manufactured This patent refers to improvements in the manufacture of adjustable potentiometers which are employed for establishing the correct value of the electrical resistance of a circuit in an electrical or electronic assembly and to the potentiometer itself which is produced in accordance with the described improvements in the manufacture.

Adjustable potentiometers which are capable of varying within certain limits the value of the electrical resistance of a circuit are produced by assembling its components which generally include a housing in an insulating material, preferably being a plastics injection moulding, the injection process being carried out independently from the production of the other components. These comprise an insulator plate carrying the resistive track, the collector and the respective terminals to which will be connected the external connection terminations, the cursor or wiper, a component for actuating the cursor and a cursor support. The whole being completed by a closure component which may coincide with the resistive track support plate.

As a general rule the manufacture of the above mentioned type of potentiometer consists of an automatic assembly process of the components which have been produced by previous independent operations. The disadvantages of this method lie in the time lag between the individual component production and the assembly stage into the complete unit, this loss of time, the manhandling and the assembling of the components adding considerably to the final cost of the potentiometer.

The improvements described herein and claimed in this invention patent result in a considerable simplification of the automated production of adjustable potentiometers, this being achieved by combining the forming of the housing and the contact terminals which connect with the resistive track and with the collector respectively, within the housing. The automated manufacturing process as described may be microprocessor controlled.

Another characteristic of the manufacturing process as described in this patent is the production of the terminals from previously stamped out metal strip, and their virtually simultaneous incorporation into the housing directly and while the latter is being formed, so being held securely to the housing, thus ensuring that the said elements retain their position and continuity of contact and connection. The remaining components making up the device are incorporated on a similar automated follow-on basis.

To facilitate the explanation this specification is accompanied by drawings showing by way of a non-limitative illustration one embodiment of the improvements in the manufacture of adjustable potentiometers and to the potentiometers so manufactured.

In the drawings: Figure 1 shows the metal strip after its stamping out in a press operation not part of this claim or patent, but showing the cut-out areas which define the terminals, which same will be the result of a subsequent operation of cutting the edges of the strip which join the various zones.

Figure 2 shows a transverse section of the strip in question, along the plane ll-ll.

Figure 3 shows the metal strip as seen in the previous figures after the application to both faces of the strip, of the housing which will contain the remaining elements of the potentiometer, this housing being the result of an injecting moulding process, in a mould through which is fed the metal strip to which the sections making up the housing remain incorporated.

Figure 4 is a longitudinal section of the assembly and Figure 5 a transverse section, through the planes IV-IV and V-V.

Figure 6 shows the housing with its incorporated terminals after cropping the metal strip, the terminals lying in the same plane.

Figure 7 is a longitudinal section of the same.

Figure 8 shows the housing with the side terminals corresponding to the extremities of the resistor track, elbowed such that their extremities remain in the same plane as the central terminal, corresponding to the collector but with a positioning suitable for the insertion of the potentiometer in a printed circuit board, for example, with figure 9 showing a longitudinal section of the assembly.

Figures 10, 11 and 12 are cross sections of the complete potentiometer with its various component parts, on the planes shown as X-X, Xl-Xl and XII-XII respectively.

Figure 13 is a plan view of the potentiometer showing its front face.

The numbers on the drawings correspond to the references indicated in the following description.

The metal strip -1- which has undergone a press operation which is not described nor claimed here, is provided with a number of perforations which predetermine the form and structure of the collector and the terminals for the external connections.

The hole -2-corresponds to the interior of the collector which will be in the form of a corona predetermined by the zones -11-. The spaces -3- determine the shape of the terminals -4- and -5-, of the indented extremities -6- and -7- and the spade ends -8- and -9- which connect to the extremities of the resistor track of the future potentiometer.

The zone -10- becomes the terminal of the collector with its indented termination -12-.

The holes -13- are for positioning and registering the metal strip -1-.

In accordance with the claimed improvements the housing of the potentiometer under construction is formed on one side and the other of the strip -1- prior to the cropping of the said strip, thus ensuring continuously the relative positions of the elements forming the collector and the terminals.

Figure 3 and figure 4 show how the part -15-of the housing is located on one of the faces of the strip 1- while the base part -14- of the future potentiom eter is formed on the other face.

The orifice -16- corresponds to the centre, providing the opening for the actuating button of the cursor support with the cursor being situated at position -17-, coaxial with the said opening.

After consolidating the housing the strip is cropped in a consecutive operation at the predetermined positions, leaving thus the three terminals deriving from the lateral part of the strip and arranged such that the subassembly so produced can accept the fitting of the remaining elements of the structure of the potentiometer; the resistive track support plate, the cursor and the other items.

The application of the improvements described herein, lead, as has been stated above, to the obtention of the support structure of the new potentiometer and this is then completed by the addition of the items mentioned below, up to the production of the completed device.

The housing of the potentiometer consists of the previously mentioned body -15-, having an orthohedric structure, with one of its major sides open, the mouth of the opening stepped such that it can accept in the stepped mouth -18- a place in insulating material, -19- which will carry the electro-resistive track and its contact elements.

The above mentioned plate -19- made preferably in alumina or in a synthetic material such as the material known commercially as melinex, is square and particularly on its functional face, has a low roughness value, of the order of 0.8 microns. The inner surface carries a resistive track of graphitic deposition -20- in the shape of an incomplete corona the extremities of which receive an application of a dissolution of silver, zones -21- and -22-, ensuring the contact under all conditions, and applied by means of a method of deposition which by providing some elasticity can withstand vibration and other action which could result in a rupture of the contact.

The internal extremities of the outer terminals -4and -5- are connected indirectly to the zones -21and -22-, which in the case illustrated corresponds to the potentiometer being mounted vertically with respect to the plane of an insulator board carrying the printed circuit.

A silver deposit forms a circular area -23-analogous to -21- and -22- in the resistive corona central to it but not touching this corona -20-, the deposit area is extended to form the zone -24- and to this is attached the output terminal -10- An alternative arrangement of the terminals is shown by the dotted lines in figure 10 allowing the potentiometer to be mounted in a horizontal plane relative to the printed circuit insulating board.

Electrical contact between the zones -21-, -22and -24- and the corresponding terminals is provided by means of stainless steel helicoidal elements -25-which are lodged within the perforations -26-, -27-, and -28- respectively, provided in the housing -15-.

The cursor or wiper -29- also is a helicoidal element with its spiral turns in contact, in stainless steel wire with its end turns bent in to the interior of the winding. It is held within the housing recess -30- of prismatic configuration, consisting of an actuating component -31- which is in the form of a circular trapezoidal button prolonged axially to an extension -32- having a diametral slot -33- for the insertion of a screwdriver or other suitable tool for purposes of turning the button and thus moving the wiper along the resistive track and thus varying the resistive value between the output terminals of the potentiometer.

So as to ensure adequate pressure of the wiper continuously against against the resistive track -20and and against the concentric zone -23-, the element -34-, a prism shaped piece in elastic material, such as a silicone, acts as a shoe, exerting pressure on the said wiper.

In the arrangement described above, the housing -15- which contains and protects the components of the potentiometer is completely enclosed by the plate -19-, thus protecting the device against extraneous agents particularly of the mechanical type, as well as against the ingress of dust and humidity. The lip -35-, obtained by swaging over the edges -36- of the housing -15-retains the plate -19in its correct position. The orifices -37- of the housing -15- are blocked off by the internal extremities of the connection terminals. The clearance between the lateral extension -32- of the wiper retention member and the circular aperture -16-, central to the front face of the housing -15- and through which the said extension passes, is kept to a minimum to prevent the ingress of dust or humidity.

Claims (6)

1. - Improvements in the manufacture of adjustable potentiometers and to the potentiometers so manufactured, characterized in that the housing body of insulating material which is the component enclosing and protecting the resistive element, the collector, the cursor or wiper and the cursor support is formed in a moulding operation which is combined with the advance of a previously die-stamped metal strip having blanked out spaces which determine the form of the future collector and the external connection terminals, one part of the housing corresponding to one face of the strip and the other part of the housing to the other face of the strip, such that there is formed an integral inseparable assembly.

2. - Improvements in the manufacture of adjustable potentiometers and to the potentiometers so manufactured, as in the previous claim, characterized in that the final configuration of the collector and of the external connection terminals associated with the housing and integral with it, is obtained by an operation of cropping or cutting of the areas delimited by the blanked out spaces in the strip, and sub-assembly consisting of the insulating housing, the collector housed therein and the external connection terminals then proceeding to receive the remaining components which complete the variable resistance device.

3. - Improvements in the manufacture of adjustable potentiometers and to the potentiometers so manufactured, as in any previous claim, character ized in that it provides for the inclusion of two helicoidal elements in stainless steel wire within cylindrical spaces in the housing with their extremities exerting pressure respectively, against the electroconductive areas associated with the terminatio!,s of the resistive track deposited on the inner face of the housing closure plate which lies on the open larger face of the said housing, and against the internal extremities of the connection terminals.

4. - Improvements in the manufacture of adjustable potentiometers and to the potentiometers so manufactured, as in any previous claim, characterized in that the cursor or wiper has the form of a constant diameter helix of stainless steel wire and is located radially within the interior of a rotating support member, the helix extremities exerting pressure respectively against the resistive track and against an electro-conductive area which is concentric to the said track.

5. - Improvements in the manufacture of adjustable potentiometers and to the potentiometers so manufactured, as in any previous claim, characterized in that the circular-trapezoidal shaped rotating cursor support member has a radial rectangular recess in which is lodged the cursor or wiper and a prism-shaped element in an elastic material which exerts on the cursor a pressure, acting as a shoe, causing it to remain in contact with the metal parts which it is designed to connect.

6. - Improvements in the manufacture of adjustable potentiometers and to the potentiometers so manufactured, substantially as hereinbefore described with reference to the accompanying drawings.