GB1567159A - Potentiometers - Google Patents

Description

(54) IMPROVEMENTS RELATING TO POTENTIOMETERS (71) We, THE PLESSEY COMPANY LIMITED, a British Company of 2/60 Vicarage Lane, Ilford, Essex, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to potentiometers and relates more specifically to improved methods of manufacturing such potentiometers, especially rotary potentiometers of the miniature type, which result in significantly lower manufacturing costs.

According to the present invention there is provided a method of manufacturing a potentiometer comprising the steps of producing on a board by a printing technique a multiplicity of track layouts each of which includes associated resistive and highly conductive tracks, separating portions of the board so that each portion bears one of said track layouts and assembling each of said board portions in association with a respective potentiometer housing which accommodates a movable wiper assembly so that the wiper for said assembly bridges the associated resistive and highly conductive tracks applied to said board portions.

In carrying out the present invention each of the board portions may have printed terminal strips which are connected with the resistive and highly conductive tracks respectively and to which terminals are fixedly secured to make electrical contact therewith said terminals extending from one edge of said board portion.

After the production of the separate board portions each of these board portions may be secured over the open end of a potentiometer housing into which a rotor and wiper assembly has previously been assembled. The assembling of the potentiometer is preferably carried out automatically by feeding the various potentiometer parts to an assembly machine.

By way of example one method of manufacturing a miniature rotary potentiometer will now be described with reference to the drawings accompanying the Provisional Specification in which: Fig. 1 shown an exploded view of a miniature rotary potentiometer manufactured by the method according to the present invention, and Figs. 2cur, 2b, 2c, 2d and 2e depict the steps in the production of the tracked board portion of the potentiometer of Fig. 1.

Referring first to Fig. 1 of the drawings the potentiometer illustrated forms the subject of our co-pending application No.

50992/75 (Serial No. 1567158).

The potentiometer comprises a rectangular open-ended preferably die-cast metal housing 1. This housing 1 is formed with four integral hollow pins two of which are indicated at 2 which are arranged to pass through holes 3 in an insulating board 4 which has applied to it by a printing process an arcuate printed resistive track 5 (e.g. screen printed conductive plastics material) and a high conductivity circular track 6 (e.g. screen printed silver). Also printed on the board 4 are high conductivity terminal strips 7, 8, 9 connected to the tracks 5 and 6. Terminals 10, 11 and 12 are staked into the terminal strips 7, 8 and 9 and to ensure good electrical therewith, lugs (not shown) are provided on the terminals which pass through slots in the board and are pressed down on to the reverse side of the board to hold the terminals securely in position on the board.

As will be appreciated the open back end of the housing 1 will be closed by the board as the ends of the hollow pins 2 passing through the board holes 3 are turned over to rivet the board to the housing. The potentiometer also includes insulating spindle 13 having a rectangular wiper carrier part 14 which has a cavity (not shown) on the face thereof adjacent the board for receiving a saddle-shaped springy metal wire wiper 15 which may be of stainless steel. In this cavity is located a wiper positioning lug (not shown) integral with the spindle which may be moulded.

As can be appreciated from the drawing, the two ends of the wiper are arranged to engage with the outer resistive track 5 and the inner high conductivity track 6, respectively. At one end 16 of the wiper the ends of the wire overlap to provide twin contacts for good contact reliability. The rear end of the spindle is rotatably supported in a hole 17 provided in the insulating board 4. The front end of the spindle passes through and is rotatably supported by a threaded boss 18 formed integrally with the die cast housing 1. The inner contours of the housing include an abutment formed integrally with the housing which limits the travel of the spindle 13 as it is rotated between limit positions in clockwise and counter-clockwise directions.

Dimensioning of the potentiometer parts is such that when the board 4 is secured against the housing 1 by turning over the aforesaid rivet pins 2, the wiper carrier structure 14 substantially abuts against the track board 7 thereby avoiding any significant free axial play of the spindle and ensuring consistency of contact pressure between the wiper and the tracks 5 and 6 of the board.

The front end of the spindle may be provided with a flat 19 to facilitate knob fixing, and the rear end 20 of the spindle may be of rectangular section to provide a key which may key into a slotted spindle end of another similar potentiometer ganged to the first potentiometer or into the slotted spindle end of a limit switch.

The further potentiometer or switch may be secured to the first potentiometer by rivets which pass through the hollow pins 2 the ends of which are turned over and corner holes in the housing of the further potentiometer or switch.

In accordance with the present invention the board 4 carrying the resistive and highly conductive tracks 5 and 6, respectively, is produced as follows, referring now to Figs.

2a, 2b, 2c, 2d and 2e of the accompanying drawings.

On a relatively large insulating board 21 (e.g. phenolic base board) a multiplicity of track layouts (e.g. 30 layouts in the present example) are produced by a silk screen printing technique to lay down resistive and highly conductive areas. Each of these track layouts includes the tracks 5 and 6 depicted in Fig. 1 with their highly conductive terminal strips 7, 8 and 9 also printed on the board. When the track layouts have been printed on the board, the printed board is cured and thereafter loaded with other printed boards into a punching and cropping machine which punches out the bearing holes 17 in the track layouts and cuts the board into six strips one of which is shown at 22 in Fig.

2b. The board may be heated by hot air in order to assist the punching operation.

These strips 22 each of which has five track layouts are then fed into a magazine from which they are transferred by a pick and place head into a further punching and cropping machine which cuts the strips into five separate board portions and punches ten holes into each board portion as shown in Fig. 2c. The holes 3 permit the passage of rivet pins as previously described and the- slots 23 allow the lugs of terminals 10, 11 and 12 (Fig. 1) to pass through the board. To assist punching the board may again be heated by hot air and during punching the previously punched central hole 17 conveniently serves as locating hole for the strip in the machine. Each of the board portions has a single track layout comprising two tracks 5 and 6 and highly conductive terminal strips 7, 8 and 9.

Terminals are then cropped from a multiterminal stamping 24 (Fig. 2d) consisting of rows of interconnected terminals and formed into individual terminals 25 with lugs 26. The terminals are then secured to the respective printed terminal strips 7, 8 and 9 by stagging the terminals into the strips and turning over the ends of the lugs 26 which extend through the slots 23 in the track board. These board portions are then passed to a grading machine which tests for track resistance and electrical continuity. The acceptable track board portions may then be stored in drum type containers in readiness for transfer to an assembly machine.

Completed board portions are then fed together with potentiometer housings and rotors to a rotary type multi-station assembly machine. In the assembly machine each rotor is inserted into a housing so that the spindle 13 (Fig. 1) passes through the boss 18 (Fig. 1) of the housing which is located in a suitable holder at one of the stations of the machine, after which the rotor is lifted momentarily whilst grease is applied for lubricating the bearing surfaces of the rotor and the housing. The springy wire wiper 15 is positioned in the cavity of the wiper carrier part 14 of the rotor before the track board portion is automatically positioned over the open end of the housing so that the hollow rivets 2 pass through the holes 3 in the board portion 4 after which the rivet ends are spun over to secure the board portion to the housing 1.The rotor may then be rotated to distribute the applied grease and the potentiometer tested before being discharged to a hopper.

As will be appreciated from the foregoing the potentiometer comprises only five different component parts and therefore lends itself extremely well to automatic assembly techniques as described above, but it should be understood that the assembly of the parts could be performed manually.

WHAT WE CLAIM IS: 1. A method of manufacturing a potentiometer comprising the steps of producing on a board by a printing technique a multiplicity of track layouts each of which includes associated resistive and highly conductive tracks, separating portions of the board so that each portion bears one of said track layouts and assembling each bf said board portions in association with a respective potentiometer housing which accommodates a movable wiper assembly to that the wiper for said assembly bridges the associated resistive and highly conductive tracks applied to said board portions.

2. A method as claimed in claim 1, in which the board portions have printed terminal strips which are connected with the resistive and highly conductive tracks, respectively, and to which terminals are fixedly secured to make electrical contact therewith, said terminals extending from one edge of the board portion.

3. A method of manufacturing a potentiometer as claimed in claim 1 or claim 2, in which after production of the separate board portions, each of the board portions is secured over the opening of the potentiometer housing into which a rotor and wiper assembly has been previously assembled.

4. A method as claimed in claim 1, 2 or 3, in which the assembling of the potentiometer is carried out automatically by feeding the various potentiometer parts to an assembly machine.

5. A method of manufacturing a potentiometer substantially as hereinbefore described with reference to the drawings accompanying the Provisional Specification.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. rotated to distribute the applied grease and the potentiometer tested before being discharged to a hopper. As will be appreciated from the foregoing the potentiometer comprises only five different component parts and therefore lends itself extremely well to automatic assembly techniques as described above, but it should be understood that the assembly of the parts could be performed manually. WHAT WE CLAIM IS:

1. A method of manufacturing a potentiometer comprising the steps of producing on a board by a printing technique a multiplicity of track layouts each of which includes associated resistive and highly conductive tracks, separating portions of the board so that each portion bears one of said track layouts and assembling each bf said board portions in association with a respective potentiometer housing which accommodates a movable wiper assembly to that the wiper for said assembly bridges the associated resistive and highly conductive tracks applied to said board portions.

2. A method as claimed in claim 1, in which the board portions have printed terminal strips which are connected with the resistive and highly conductive tracks, respectively, and to which terminals are fixedly secured to make electrical contact therewith, said terminals extending from one edge of the board portion.

3. A method of manufacturing a potentiometer as claimed in claim 1 or claim 2, in which after production of the separate board portions, each of the board portions is secured over the opening of the potentiometer housing into which a rotor and wiper assembly has been previously assembled.

4. A method as claimed in claim 1, 2 or 3, in which the assembling of the potentiometer is carried out automatically by feeding the various potentiometer parts to an assembly machine.

5. A method of manufacturing a potentiometer substantially as hereinbefore described with reference to the drawings accompanying the Provisional Specification.