GB2073494A

GB2073494A - Electrical keyswitch

Info

Publication number: GB2073494A
Application number: GB8110124A
Authority: GB
Original assignee: Schoeller and Co Elektrotecnische Fabrik GmbH and Co
Current assignee: Schoeller and Co Elektrotecnische Fabrik GmbH and Co
Priority date: 1980-04-03
Filing date: 1981-04-01
Publication date: 1981-10-14
Also published as: DE3013115C2; FR2480027A1; IT8120761A0; IT1136868B; DE3013115A1; FR2480027B1; GB2073494B

Abstract

A keyswitch comprises a housing (5), a key (6), and a spring member (1, 2) which is formed as a one piece double spring having an outer part (1) which is preferably cylindrical and an inner, preferably conical, part (2). The outer part (1) acts as a return spring for the key (6) and may also be electrically connected to a terminal contact (8) whilst the inner part (2) may form a movable contact and act upon a central contact (7) either directly or via a snap acting contact disc, so that when the key (6) is depressed the part (2) establishes an electrical connection between the contact pair (7, 8). The inner part (2) of the spring may alternatively act upon a flexible layer carrying a movable contact which is cooperable with a fixed contact on a printed circuit board. <IMAGE>

Description

SPECIFICATION Electrical keyswitch The present invention relates to an electrical key- switch and is particularly suitable for use in electronic devices, for use with contact foils and for use on keyboards, the keyswitch having a helical return spring for the key and a contact pressure spring located between the contact of the switch and the key.

A known electrical keyswitch (US-PS 37 73 998) has two spiral shaped springs, one of these having a larger diameter than the other and acting as a return spring for the key, while the other spring is located within the return spring between the contact of the switch and the key and forms the contact pressure spring. This known switch is disadvantageous in that two separate springs are required to reset the key and to operate the contact.

It is an object of the present invention to improve the known switch and to provide a single spring that will both reset the key and operate the contact, enable a large stroke, define an exact switching position after a certain stroke path and have a defined overstroke.

According to the present invention there is provided an electric keyswitch, particularly suitable for use in electronic devices, for use with contact foil and for use on keyboards, the keyswitch including a helical return spring for the key and a contact pressure spring located between the contacts of the switch and the key, the return spring and the contact pressure spring being made from one unit and forming a double spring.

The switch according to the present invention has the advantage of being simple to contruct and cheap to produce, the assembly of the double spring is quick and easy and it has a long life expectancy. The switch of the present invention is particularly beneficial when used in mini-switches where small contact systems are required but a relatively large key stroke is still demanded.

An advantageous development of the present invention provides that the inner contact pressure spring is wound into the shape of a cone and projects into the interior of the return spring. The last coil of the larger outer spring can be supported by one of the electric contacts, and when the key is depressed, the last coil of the inner spring touches the other contact, which is located centrally and an electrical connection is thereby produced. The part of the double spring that forms the contact pressure spring can be shorter than the part of the return spring that surrounds it and this, thereby, produces a delayed electrical contact. The inner spring, which activates the central contact, can have a greater force than the outer spring, which is acting as the return spring.When depressed, the inner spring can activate a snap disc as the contactor with feedback pulses and this enables the greatest possible stroke to be obtained.

The last coil of the larger outer spring can be supported by the contact disc and.retain it in position. When the contact position has been reached, the inner spring, when further depressed, can deflect and increase the contact pressure and generate a precisely defined overstroke. When the double spring is used in keyboards with cqntact foils, the diameter of the outer spring can be larger than the diameter of the contact space beneath the contact foil. When activated, the inner spring can force the contact foils through the contact space thereby establishing an electrical connection between the contact surfaces.

The present invention will be further described, by way of example, with reference to the accompanying drawings, in which: Figure lisa side view of a double spring; Figure2 shows a longitudinal section of a keyswitch on the "OFF" position; Figure 3 shows a plan view of the double spring and the contacts of the switch as shown in Figure 2; Figure 4 is the switch as in Figure 2 in the "ON" position; Figure 5 is a longitudinal section of a further development of the keyswitch with a contact spring disc in the "OFF" position; Figure 6 is the switch as in Figure 5 in the "ON" position; Figure 7 is a longitudinal section of a third development of the keyswitch with a contact foil in the "OFF" position; and Figure 8 is the switch as in Figure 7 in the "ON" position.

The spring illustrated in Figure 1 consists of a cylindrical part 1 and a frusto-conically shaped part 2, which part 2 is in an inverted position within the cylindrical part 1,whereby both parts are wound from a piece of spring wire and form one unit. The outer part 1 could be conical and the inner part 2 cylindrical, or both parts could be wound into a cone shape. The part 2 of the double spring is shorter than the part 1, this enables a delayed electrical contact to be produced. This delay can be determined precisely in advance and depends on the dimensions of both spring parts. As far as force is concerned, the inner part 2 is stronger than the outer part 1.

Figure 2 shows a keyswitch incorporating the double spring referred to in Figure 1. The switch comprises a housing 5, a key 6 in the housing 5, two fixed contacts 7 and 8 inserted in the housing, and two connecting terminals 9 and 10. The double spring is located between the key 6 and the two contacts 7 and 8, the outer part 1 of which forms the return spring for the key 6 and the inner part 2 of which forms the moving contact. When the key 6 is depressed, the lower end of the inner part 2 of the double spring touches the fixed contact 7, as can be seen in Figure 4 and the inner part 2 of the double spring provides the contact pressure necessary to ensure conduction in the contact position. The outer part 1 touches the fixed contact 8 in such a way that when the double spring is in the depressed contact position, it forms a contact bridge between the fixed contacts 7 and 8.Lateral projections 11 and 12 are provided on the key 6 and act as stops limiting the key stroke and, as shown in Figures 7 and 8, they also guide the key 6 in the housing 5. When the contact position has been reached, the inner part 2 of the double spring, when depressed further, is compressed and the contact pressure is increased. As can be seen in Figures 5 and 6, the outer part 1 of the double spring can also touch a spherical, catotte- shaped spring contact disc 15. As shown in Figure 6, when the key 6 is operated, the inner part 2 of the double spring is pressed onto the contact spring disc 15, which acts as the contact bridge between the fixed contacts 7 and 8. Thus, the bottom coil of the larger outer spring 1 is supported by the contact disc 15 and retains it in position.

The development illustrated in Figures 7 and 8 is particularly for use on keyboards with contact foils and with several keys located in rows next to one another and one upon the other. In this arrangement, the switch housing 20 is located on a plate 21 with a printed circuit board 22, which contains the fixed contact 23. The moving contacts 24 are to be found on a contact foil 25, which is located on a perforated spacing plate 26. The spacing plate 26 being fixed on a base plate 21. The outer large coil part 1 of the double spring sits on the contact foil 25 and when the key 6 is depressed (Figure 8) the inner part 2 exerts a spring pressure onto the contact surface 24 and forces it through the space 27 so that the current can be transferred to the contact position 23.

Several examples of the present invention have been illustrated; however, it is understood that the present invention is not limited in any way to these examples, as there are numerous variations possible using the double spring and the other components and there are also numerous possibilities in the design of the switch, none of which would deviate from the present invention.

Claims

1. An electric keyswitch, particularly suitable for use in electronic devices, for use with contact foils and for use on keyboards, the keyswitch including a helical return spring for the key and a contact pressure spring located between the contacts of the switch and the key, the return spring and the contact pressure spring being made from one unit and forming a double spring.

2. A keyswitch as claimed Claim 1, in which the inner contact pressure spring is wound into the shape of a cone and projects into the interior of the return spring.

3. A keyswitch as claimed in Claim 1 or 2, in which the last coil of the larger outer spring is supported on one of the electrical contacts and when the key is depressed, the last coil of the inner spring touches the other contact, which is located centrally, thereby producing an electrical connection.

4. A keyswitch as claimed in Claims 1 to 3, in which the part of the double spring which forms the contact pressure spring is smaller than the part of the return spring that surrounds it, which produced delayed electrical contact.

5. A keyswitch as claimed in Claims 1 to 4, in which the inner spring, which activates the central contact is stronger and has more force than the outer spring, which acts as the return spring.

6. s A keyswitch as claimed in Claims 1 to 5 in which when depressed, the inner spring oan activate in a delayed manner a snap disc as the contactor with feedback pulses, which enables switches of this type to have a large stroke.

7. A keyswitch as claimed in Claim 6, in which the last coil of the larger outer spring is supported by the contact disc and retains it in position.

8. A keyswitch as claimed in Claims 1 to 7, in which when the contact position has been obtained, the inner spring, when depressed further, is compressed and increases the contact pressure and achieves a precisely defined overstroke.

9. A keyboard with keyswitches according to any of the Claims 1 to 8 with contact foils, in which the diameter of the outer double spring is larger than the diameter of the contact space beneath the contact foil.

10. A keyboard as claimed in Claim 9, in which, when depressed, the inner spring forces the contact foils through the space thereby creating an electrical contact at the contact surfaces.

11. A keyswitch substantially as herein described with reference to and as illustrated in the accompanying drawings.