GB2298315A

GB2298315A - Rotary switch

Info

Publication number: GB2298315A
Application number: GB9503318A
Authority: GB
Inventors: Ying Wai Yu
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-02-21
Filing date: 1995-02-21
Publication date: 1996-08-28
Also published as: GB9503318D0

Abstract

A rotary switch comprises a rotary shaft 12 , a collar fitted onto the shaft, a spring 22 mounted around the shaft 12 so as to be compressed by the collar and a switch contact 24 mounted on the shaft so as to be rotatable therewith and being biased against a printed circuit board 18 by the spring 22. The collar may be retained on the shaft 12 by a screw, by a shoulder on the shaft or by a necked portion on the shaft receiving a C-shaped collar. Alternatively, the collar may be snap fitted over a deformable portion of the shaft having a slot which, after the collar has been fitted, is filled with material to hold the collar in position.

Description

ROTARY SWITCH This invention relates to a rotary switch and in particular to a rotary switch having a rotary shaft with deformable retaining means provided thereon.

A known type of rotary switch consists of a rotary shaft having a threaded portion provided at the free end thereof and a nut threadably engaged to the threaded portion of the rotary shaft to hold a spring on the rotary shaft.

A disadvantage of this known kind of rotary switch is that the screwing of the nut onto the shaft is a rather time consuming process. In addition, the screw procedure maybe incorrectly carried out. Since the nut is used to hold the spring in a suitable compressed state, incorrect placing of the nut with respect to the pin may result in a drop in performance of the final product. Also, the rotary shaft and nuts are usually fabricated from metal and their production costs are high.

A second known kind of rotary switch is described in granted British patent number 2211996, the contents of which are incorporated into this specification by way of this reference.

A disadvantage of the known kind of rotary switch described in British patent number 2211996 is that the spring is retained on the rotary shaft by means of a collar which snap fits over a deformable retaining means provided on the end of the rotary shaft. The retaining means generally comprises a spear member formed from a plastics material. The collar may be separated from the retaining means as the elasticity of the spear member gradually decreases with time.

According to the present invention there is provided a rotary switch adapted to frictionally hold a metal switch contact against a printed circuit board, said switch comprising a rotary shaft having a first end and a second end; spring means mounted around said shaft between said first end and said second end; retaining means provided on or towards the second end of-the shaft, collar means adapted to fit onto the shaft, and engageable with the retaining means to be retained on said shaft, and a switch contact mounted on said shaft to be rotatable therewith, the switch contact being biassed into an operating position by said spring means which is compressed by said collar means, said retaining means being formed separately from said rotary shaft and adapted to co-operate with said shaft to maintain said spring means in a compressed state, without requiring substantial deformation of the rotary shaft.

The retaining means in the rotary switch of the present invention does not depend therefore on any deformation of the rotary shaft. This means that the collar is likely to remain retained on the rotary shaft over a longer period of time, and the strength of the retention of the collar on the rotary shaft does not now depend on the elasticity or deformability of the rotary shaft.

The rotary shaft may be formed from any suitable material such as a plastics material or from metal or wood.

Alternatively the retaining means may comprise a screw adapted to be engaged with the second end of the rotary shaft. When the screw is engaged with the rotary shaft, the screw serves to compress the spring means.

Whilst the retaining means may comprise a screw, it is not necessary for the rotary shaft to be formed with a screw thread, as the screw will engage with the second end of the rotary shaft. This means that manufacturing costs of the rotary switch are low, and manufacturing rates are high, and the reject rate of substandard switches is low.

The screw will typically be made from a hard material such as a metal alloy or other suitable hard material. The rotary shaft will generally be made from a soft material such as a plastics material. When the screw is pushed as it is turned, it is able to turn down into the shaft so that it can engage with the second end of the shaft.

Preferably, the rotary shaft has a first shaft portion at the second end of the shaft which has a cross sectional shape having a transverse dimension which is substantially longer than a longitudinal dimension and a second shaft portion being smaller than the first shaft portion at least in one dimension to define a shaft shoulder extending either partially or completely around the second shaft portion and extending from a surface of a first shaft portion, and the collar means comprises an outer collar defining an aperture having a shape corresponding to the cross sectional shape of the shaft.

In use, the collar may be positioned such that the transverse dimension of the internal aperture is placed in a corresponding orientation to the transverse dimension of the cross sectional shape of the rotary shaft. In this position the collar may then be pushed onto the rotary shaft. The collar may be retained in position by turning the collar preferably through substantially 900, the collar then being held in place on the shaft shoulder.

Alternatively, the rotary shaft comprises two notches spaced apart from one another to define a neck portion between a first shaft portion and a second shaft portion, the neck portion having a width in a particular dimension and the collar means comprises a substantially C-shaped collar the ends of the C being spaced apart from one another by a distance substantially equal to the width of the neck.

The C-shaped collar further comprises a projection formed on a surface of the collar running substantially completely along the length of the surface such that in use the projection is formed on an upper surface of the collar, and serves as an abutment for the spring means thus holding the spring means in a compressed state. The projection also serves to hold the collar in position on the rotary shaft.

The rotary shaft may comprise an initially deformable retaining means provided on the second end of the shaft, and the collar means has a collar aperture adapted to snap over said retaining means so as to be retained on said shaft, the retaining means normally having a retaining dimension exceeding a dimension of said collar aperture and being inwardly deformable to a dimension less than the dimension of the said collar aperture, and the retaining means taking the form of a spear member having a slot extending longitudinally along a plane parallel to the axis of the rotary shaft, the switch further comprising a material adapted to fill a space defined by said slot, which material is then integrated with the shaft and the collar means by means of any suitable method such as in a chemical manner or by welding or binding.

The embodiments of the invention will now be further described by way of example only with reference to the accompanying drawings in which: Figure 1 is a schematic representation of a first embodiment of the invention in which the spring means is held in place by means of a screw; Figure 2 is a schematic representation of the second embodiment of the invention in which the spring means is held in position by means of a collar in the form of a ring; and Figures 3a to 3d are schematic representations of a third embodiment of the invention in which the spring means is held in position by means of a collar means held in notches in the rotary shaft.

Referring to Figure 1 a rotary switch is designated generally by the reference numeral 10.

The rotary switch 10 conaists of a rotary shaft 12 with a regulating knob member 14 integrally provided thereon at one end thereof. An elongate groove 20 is disposed on the upper surface of the knob member 14 to facilitate rotation of the rotary shaft 12 by means of a screw driver or other sharp edged tool. The rotary shaft 12 is adapted to journal through an aperture 16 incorporated on a printed circuit board 18. A printed circuit (not shown) is provided on the bottom surface of the printed circuit board 18.

A piece of metal switch blade or switch contact 24 is mounted on the rotary shaft 12 for rotation therewith. Switch contact 24 is in operative relation to the circuit of the printed circuit board 18, whereby turning the switch contact 24 relative to the printed circuit board 18 at indicated intervals gives rise to various switch connections.

The spring 22 is mounted on the rotary shaft 12 and is adapted to urge the switch contact 24 against the printed circuit board 18 under the influence of the spring.

Provided on the other end of the rotary shaft 12 is a retaining means generally represented by reference numeral 26. The retaining means 26 in Figure 1 is in the form of a screw, for example, a cup head wood screw which is engageable with the end of the rotary shaft. The screw serves to compress the spring means.

Turning now to Figure 2, a second embodiment of rotary switch 10 is shown. Corresponding reference numerals have been used to denote corresponding parts of the rotary switch.

The rotary shaft 12 has a first portion 200 positioned towards a first end of the shaft, and a second portion 210 positioned towards the second end of the rotary shaft. The cross sectional shape of tho second portion 210 comprises a shape having a transverse dinon:liotl which is substantially greater than the longitudinal dimension. The first portion 200 of the shaft 12 is co-axial with the second portion 210, but is shaped and dimensioned such that a rim or shoulder (not shown) is formed where the portion 210 protrudes beyond the outer surface of the portion 200.

The collar means comprises a collar having an internal aperture shaped to correspond to the cross sectional shape of portion 210. The collar may be mounted onto the shaft 12 by sliding the collar 220 onto the shaft 12 at portion 210. When the collar has moved along the length of portion 210 it arrives at the shoulder formed at the border between portion 200 and 210.

At this point the collar 220 may be turned through an angle which causes the shorter dimension of the aperture 230 to align with the longer dimension of the cross sectional shape of the portion 210. This means that the collar portion will rest on the shoulder and will be retained in place maintaining the spring in a compressed state.

Turning now to Figure 3, a third embodiment of the rotary switch according to the present invention is shown.

The rotary shaft 12 comprises two notches 310, 320 formed on opposite sides of the shaft 12 from one another and spaced apart from one another by a distance L shown in Figure 3a. The retaining means comprises a collar which is substantially C shaped, having ends 330, 340 which are spaced apart from one another by a distance approximately equal to the distance L.

On one surface 350 of the collar 360, a projection is formed.

The collar may be inserted onto the rotary shaft 12 by aligning the free end 330, 340 with the notches 310, 320, and sliding the collar 360 onto the shaft 12. The projection 370 will then project above the level of the collar, and will come into contact with the spring 22 and serve to maintain the spring in a compressed state and to fix the position of the C-shaped collar.

In the fourth embodiment not shown, the collar means may be held in position by means of welding or from a chemical reaction or other form of binding.

Claims

1. A rotary switch adapted to frictionally hold the metal switch contact against the printed circuit board, said switch comprising a rotary shaft having a first end and a second end; spring means mounted around said shaft between said first end and said second end; retaining means provided on or towards the second end of the shaft, collar means adapted to fit onto the shaft, and engageable with the retaining means to be retained on said shaft, and the switch contact mounted on said shaft to be rotatable therewith, the switch contact being biassed into an operating position by said spring means which is compressed by said collar means, said retaining means being formed separately from said rotary shaft and adapted to co-operate with said shaft to maintain said spring means in a compressed state, without requiring substantial deformation of the rotary shaft.

2. A rotary switch as claimed in claim 1 wherein the rotary shaft is formed from

3. A rotary switch as claimed in claim 1 wherein the retaining means comprises a screw adapted to be engaged with the second end of the rotary shaft.

4. A rotary switch as claimed in any one of the preceding claims wherein the rotary shaft has a first shaft portion at the second end of the shaft which has a cross sectional shape having a transverse dimension which is substantially longer than a longitudinal dimension and a second shaft portion being smaller than the first shaft portion at least in one dimension to define a shaft shoulder extending either partially or completely around the second shaft portion and extending from a surface of the first shaft portion, and the collar means comprising an outer collar defining an aperture having a shape corresponding to the cross sectional shape of the shaft.

5. A rotary switch according to any one of claims 1 to 3 wherein the rotary shaft comprises two notches spaced apart from one another to define a neck portion between a first shaft portion and a second shaft portion, the neck portion having a width in a particular dimension and the collar means comprising a substantially C-shaped collar, the ends of the C being spaced apart from one another by a distance substantially equal to the width of the neck.

6. A rotary switch as claimed in claim 5 wherein the Cshaped collar further comprises a projection formed on a surface of the collar running substantially completely along the length of the surface such that in use the projection is formed on an upper surface of the collar, and serves as an abutment for the spring means thus holding the spring means in a compressed state.

7. A rotary switch as claimed in any one of claims 1 to 3 wherein the rotary shaft comprises an initially deformable retaining means provided on the second end of the shaft, and the collar means has a collar aperture adapted to snap over said retaining means so as to be retained on said shaft, the retaining means normally having a retaining dimension exceeding a dimension of said collar aperture and being inwardly deformable to a dimension less than the dimension of said collar aperture, and the retaining means taking the form of a sphere member having a slot extending longitudinally along a plane parallel to the axis of the rotary shaft, the switch further comprising a material adapted to fill a space defined by said slot, which material is then integrated with the shaft and the collar means.

8. A rotary switch as claimed in claim 7 wherein the material is integrated with the shaft and the collar means by any suitable method such as in a chemical manner, or by welding or binding.

9. A rotary switch substantially as hereinbefore described and with reference to the accompanying drawings.