Cam Actuated Switch Having Movable And Fixed Contacts On Circuit Board

Abstract

A cam actuated switch apparatus is described in which both its movable and fixed switch contacts are mounted on a printed circuit board providing the electrical circuit to which the switch contacts are connected. One embodiment of the switch apparatus employs a cam actuator in the form of a rotatable drum having cam elements projecting from the periphery thereof for engagement with the movable contacts. In another embodiment the cam actuator is in the form of a sliding cam member which moves parallel to the surface of the printed circuit board to actuate the movable contacts thereon. As a result of mounting all the switch contacts directly on the printed circuit board there is a considerable reduction in lead inductance, capacitance, and series resistance, which enables the present switch apparatus to be used with circuits of higher frequency response. In addition, this also greatly reduces the number of soldered connections for the switch which makes it faster and less expensive to install and easier to repair, and provides the switch with greater reliability.

Description

BACKGROUND OF THE INVENTION

The subject matter of the present invention relates generally to electrical switches and in particular to cam actuated switches in which the movable and fixed contacts of the switch are mounted on a printed circuit board. The term "printed circuit board" as used herein includes circuit boards made by photoresist masking and etching or other techniques in which the electrical conductors of a circuit are formed as conductive strips on a surface of a support plate of insulating material which may or may not have electrical circuit components, such as resistors, capacitors, and transistors, mounted thereon.

The switch apparatus of the present invention is especially useful for circuits in a cathode ray oscilloscope. By providing the movable and fixed switch contacts on the printed circuit board, such contacts may be mounted closer to the circuit elements being switched. This reduces lead inductance and series resistance, and also reduces the contact capacitance to ground and to adjacent elements, thereby enabling a higher frequency response for the circuit to which the switch is connected. In addition, the number of soldered connections for the switch is greatly reduced, since the fixed contacts may be formed as part of the printed circuit and the movable contacts are soldered directly to the printed circuit board without the use of conventional interconnecting wires. As a result of this reduction in the number of soldered connections, the present apparatus is quicker and less expensive to install, is easier to repair, and is of higher reliability.

Previously some rotary switches have been made which employ a stator member in the form of a printed circuit board having fixed contacts provided thereon. However these switches differ from the present switch in that their movable contacts are mounted on a separate rotor member, as shown in U. S. Pat. No. 3,031,541 of W. H. Hoffmann. These prior rotary switches have a concentricity alignment problem which is avoided in the present switch, since in the prior switch the rotor and stator members must be mounted coaxial and concentric to enable the contacts to engage one another properly. Also because the movable contacts slide across the surface of the printed circuit board, such rotary switches require greater torque and have a shorter lifetime than the switch of the present invention, in which only the cam elements engage the movable switch contacts briefly. As a result of the lower torque, the switch of the present invention may be made with a smaller knob, requiring less mounting space on the front panel of the oscilloscope.

It is therefore one object of the present invention to provide an improved electrical switch in which the movable and fixed switch contacts are mounted directly on a printed circuit board.

Another object of the present invention is to provide an improved cam actuated switch having a fewer number of soldering connections to provide greater reliability and to reduce installation time and cost.

A further object of the present invention is to provide an improved cam actuated switch of lower inductance, smaller series resistance, and lower capacitance to enable it to be used in a circuit of higher frequency response.

An additional object of the present invention is to provide a rotary switch of long, useful lifetime which requires less torque to operate.

Still another object of the present invention is to provide a cam actuated switch having a plurality of fixed and movable contacts mounted directly on a printed circuit board and which employs either a rotary or a sliding cam member to operate the movable contacts, thereby enabling a large number of switching functions to be performed in a relatively small mounting space.

BRIEF DESCRIPTION OF DRAWINGS

Other objects and advantages of the present invention will be apparent from the following detailed description of certain preferred embodiments thereof which are shown in the attached drawings of which:

FIG. 1 is a plan view showing one embodiment of the switch apparatus of the present invention employing a rotary drum cam actuator with parts broken away for clarity to show some of the switch contacts;

FIG. 2 is a horizontal section view taken along the line 2-2 of FIG. 1, showing the switch on an enlarged scale;

FIG. 3 is a vertical section view taken along the line 3-3 of FIG. 2;

FIG. 4 is a vertical section view taken along the line 4-4 of FIG. 2;

FIG. 5 is an enlarged view of a portion of FIG. 3, showing the camming operation of the movable contact;

FIG. 6 is an elevation view of another embodiment of the switch apparatus of the present invention in which a sliding cam actuator is employed, with parts broken away for clarity;

FIG. 7 is a vertical section view taken along the line 7-7 of FIG. 6 with parts broken away for clarity; and

FIG. 8 is a horizontal section view taken along the line 8-8 of FIG. 6.

DESCRIPTION OF PREFERRED EMBODIMENT

As shown in FIGS. 1 and 2, one embodiment of the cam actuated switch apparatus of the present invention includes a rotary drum cam actuator 10 and a plurality of pairs of movable switch contacts 12 and fixed switch contacts 14 mounted on a printed circuit board 16, so that the switch contact pairs are longitudinally spaced along the axis of such cam drum. The cam drum 10 is provided with a plurality of sets of raised cam elements 18 with each cam element projecting radially outward and extending in an arc a short distance about the circumference of such drum. The sets of cam elements 18 are longitudinally spaced from one another along the axis of the cam drum and positioned so that at least one set of such cam elements engages each of the movable contacts 12 when the drum is rotated. Each of the sets of cam elements 18 may be formed on a separate member with a plurality of such members assembled into drum 10, but this create alignment problems. Therefore it is preferable to form all of the sets of cam elements integrally into the drum 10 by molding or cutting from a suitable plastic material, such as the acetyl resin known as DELRIN.

The cam drum 10 is fixedly attached at one end to a control shaft 20 for rotation therewith as hereafter described. The control shaft 20 extends through a metal bearing 21 in a front bushing 22 and a C ring 25 is clipped into an annular notch in the shaft on the opposite side of such bushing from the cam drum to prevent longitudinal movement of such shaft. A rear bearing member 24 fixedly attached to the other end of the cam drum 10 extends into a rear bushing 26. The front and rear bushings 22 and 26 on which the cam drum is rotatably mounted, may be of plastic material and are attached to the printed circuit board by mounting screws 28. A dust cover 30 of aluminum or other suitable metal, is positioned over the cam drum 10 and secured by screws 32 to the front and rear bushings. The bushings 22 and 26 are each provided with three projections 34 and 36, respectively, including two side projections which extend through slots in the opposite sides of the cover 30 and a bottom projection which extends through a hole in the printed circuit board, for additional support and for more accurate spacing of such bushings.

The control shaft 20 is keyed to a rotary detent member 37 fixedly attached to the front end of the cam drum 10 for rotation of such detent member and cam drum by means of a knob 38 attached to the opposite end of such shaft by a set screw 39. As shown in FIG. 4, the detent member 37 is provided with a plurality of detent notches 40 at its outer periphery which engage a spring biased detent roller 42. The detent roller 42 is held by leaf spring 44 extending between spaced shoulders 45 on the front bushing 22 so that such roller engages the detent notches 40 and moves vertically within a slot provided in guide portion 47 of the front bushing. A stop member 46 is provided, having a square opening keyed to a similar shaped shank portion of the detent number 37 for rotation therewith. A stop projection 48 on the stop member engages a stop provided on the front bushing 22 adjacent guide portion 47 to limit rotation of the cam drum 10 to slightly less than 360.degree..

The printed circuit board 16 is provided with a plurality of conductive strips 50 of copper or other suitable metal provided on the surface of one or both sides of a sheet of plastic insulating material in a conventional manner such as by chemically etching through a photoresist mask. The conductive strips 50 form the conductors of an electrical circuit and may be connected to circuit components 52 such as resistors, capacitors, transistors, etc. which are mounted on the printed circuit board in a conventional fashion with the leads of such components extending through holes provided in the printed circuit board and soldered to portions of the conductive strips surrounding such holes. However, it is also possible that the printed circuit can consist solely of conductive strips 50 without any circuit components 52.

The fixed switch contacts 14 are provided by some of the conductive strips 50 and formed as part of the printed circuit board on one side of such board, as shown in FIG. 5. However, the movable contacts 12 are formed separately from the printed circuit board and later soldered thereto. The movable contacts 12 are made of a suitable metal to provide a resilient leaf spring member which is spot welded to a metal mounting pin 54. The mounting pin 54 is inserted through an aperture in the printed circuit board so that the enlarged head of such pin engages such one side of such board and a soldered connection is formed between such pin and a conductive strip 50 on the opposite side of the printed circuit board to fixedly attach the mounting pin 54 and one end of the movable contact 12 to such circuit board.

The movable contact 12 includes a raised cam engaging portion 56 in the form of an inverted V intermediate the ends of the contact. A bifurcated contact portion 58 is provided at the free end of the movable contact, which moves into and out of engagement with the fixed contact 14 when the cam element 18 engages and disengages portion 56. The bifurcated contact portion 58 extends in an arc downward from an intermediate portion 60 which extends between portions 56 and 58 substantially coplanar with the fixed end of the movable contact in its unflexed condition. Thus, the free end 58 of the movable contact 12 is laterally displaced from the fixed end and the intermediate portion 60, and such free end engages the fixed contact 14 at a wide contact area extending along the major dimension of the lateral cross section of such movable contact. When the cam drum 10 rotates to cause a cam element 18 to engage the raised portion 56 of the movable contact 12, such contact is bent downward into position 12', causing the bifurcated end portion 58 of such movable contact to engage the fixed contact 14 with a slight longitudinal sliding movement due to the resulting increase in length of such movable contact which wipes the contact area free of any oxide or dirt, as shown in FIGS. 3 and 5.

Another embodiment of the switch apparatus of the present invention includes a two position slide switch having a sliding cam actuator which is shown in FIGS. 6 to 8. A printed circuit board having movable and fixed switch contacts mounted thereon similar to that previously described is also used in this second embodiment and for this reason the same reference numerals have been used as in FIGS. 1 to 5 to indicate these elements in FIGS. 6 to 8 without any further description thereof. A sliding cam member 62 having four laterally spaced cam portions 64 provided on the bottom thereof, is attached to a control shaft 66 by a coupling member 68. The coupling member 68 may be in the form of a plastic sleeve having a pair of spaced end flanges between which the U-shaped end of actuator arm portion 70 of the cam member 62 is positioned. The coupling member 68 is fixedly secured to the control shaft 66 by a set screw 72 so that longitudinal movement of such shaft by knob means 74 causes longitudinal movement of the cam actuator arm 70, as indicated by direction arrows 76, between the position shown in solid lines to the position 70' shown in phantom lines. This causes the cam portions 64 to slide across the surface of their movable contacts 12 and engage their raised portion to move such contacts downward into engagement with the fixed contacts 14. As shown in FIG. 8, the cam portions 64 are longitudinally displaced from one another so that two of the cam portions urge their corresponding movable contacts into engagement with the fixed contacts in one switch position of the cam member 62, while the two other cam portions urge their movable contacts into engagement with the fixed contacts in the other switch position.

A guide member 78 for guiding the movement of the cam member 62 is attached to the circuit board 16 and provided with a slot 80 in its upper surface of sufficient length to enable movement of the cam actuator arm 70 within such slot between the two switch positions. The guide member 78 is provided with a guideway 82 in which the cam member 62 slides longitudinally with the bottom of such guideway engaging the lower surface of the cam member 62 immediately adjacent the opposite sides of the group of four cam portions 64 to space such cam portions the proper distance from the printed circuit board 16. Connector pin portions 84 of deformable plastic material are provided on the bottom of the guide member 78 for insertion through holes in the printed circuit board to attach such guide member to such circuit board. The guide member 78 may be molded of a suitable plastic material, such as acetyl resin known as DELRIN, while the cam actuator member 62 may be molded of a somewhat harder plastic material, such as a glass particle filled nylon.

It will be obvious to those having ordinary skill in the art that many changes may be made in the above described details of the preferred embodiment of the present invention without departing from the spirit of the invention. For example other cam actuators may be employed, such as pushbutton actuators including those which move perpendicular to the printed circuit board. Also switch actuators other than cams can be employed, such as a solenoid actuator, or a movable permanent magnet actuator (in which case the switch may be a reed switch having magnetic contacts), or a simple manual actuator directly attached to the movable contact. Therefore the scope of the present invention should only be determined by the following claims.

Claims

We claim:

1. A switching device comprising a printed circuit board having a plurality of conductive paths insulatively spaced from one another thereon, stationary contact members on said board and being part of at least some of said conductive paths, movable contact members having first sections connected to at least some others of said conductive paths and second sections including contact-engaging parts disposed so as to be connected with or disconnected from respective ones of said stationary contact members, said contact-engaging parts and said stationary contact members engaging each other at a contact area substantially greater than the thickness of each of said contact-engaging parts, mounting means mounted on said board adjacent said contact members and on the same side of said board on which said contact members are mounted, actuator means movably mounted in said mounting means for movement relative to said contact members, camactuating means provided on said actuator means for selectively engaging said second sections of said movable contact members for moving said contact-engaging parts into and out of engagement with said stationary contact members as said actuator means is moved relative to said contact members, and cam-engaging means provided by each of said second sections of said movable contact members for engagement by said camactuating means when said actuator means is moved relative to said contact members thereby causing said contact-engaging parts to wipingly move along said stationary contact members.

2. A switching device according to claim 1 wherein said actuator means comprises drum means rotatably mounted in said mounting means.

3. A switching device according to claim 1 wherein said actuator means comprises a sliding member slidably mounted in said mounting means and said mounting means define guide member means for guiding said sliding member along said contact members.

4. A switching device according to claim 1 wherein stop means are provided by said mounting means and said actuator means to stop movement of said actuator means thereby limiting movement of said actuator means.

5. A switching device according to claim 1 wherein means are provided by said mounting means and said actuator means to maintain said actuator means in a selected position.

6. A switching device according to claim 1 wherein said second sections of said movable contact members define leaf spring members and said cam-engaging means define inverted V-shaped sections in said second sections.