Patent Publication Number: US-4097702-A

Title: Cam actuated switch

Description:
This invention relates to cam actuated electric switches and more particularly to reversible rotary snap action switches. 
     It is an object of this invention to provide an improved rotary switch having a cam actuated switch contact which has snap-action operation in one direction of rotation. 
     Another object of this invention is to provide an improved rotary switch wherein a cam follower is forced rapidly radially inward past a cam surface by one spring arm carrying an electrical contact when the switch is to be opened and is moved axially by another spring arm and the cam surface when the switch is moved from the open position toward the closed position. 
     A further object of this invention is to provide an improved cam actuated reversible rotary switch which has a step surface on the cam surface to allow snap-action opening of the switch contacts and a ramp surface on the cam surface to enforce closing and wiping action of the contacts. 
    
    
     These and other objects and advantages of the present invention will be more apparent from the following description and drawings in which: 
     FIG. 1 is an elevational plan view of the switch; 
     FIG. 2 is a view taken along line 2--2, FIG. 1; and 
     FIG. 3 is a perspective view of the cam portion of the switch. 
    
    
     Referring to the drawings, there is shown in FIGS. 1 and 2 a switch assembly 10 having a cam member 12, a bifurcated moveable switch arm 14 and a pair of stationary switch contacts or terminals 16 and 18. As best seen in FIG. 2 the arm 14 has a singular base portion 20 which is adapted to be secured via fasteners 21 to a stationary member. An electrical terminal 22 is formed on the singular base member 20. The switch arm 14 has a pair of contact spring arms 24 and 26 which extend from the base member 20 and have secured thereto electrical switch contacts 28 and 30 adapted to contact the terminals 16 and 18 respectively. The switch contact arm 24 has formed integrally therewith and disposed normally thereto a spring arm 32, the switch spring arm 26 has formed integrally therewith and disposed normally thereto a spring arm 34. Each of the spring arms 32 and 34 have integrally formed therewith cam followers 36 and 38 respectively. The cam followers 36 and 38 are in sliding contact with the external circumferential surface 40 of the cam member 12 and are maintained in this position by the spring force in the arms 24, 26. 
     The cam member 12 has two cam profiles 42 and 44 formed therein. The cam profiles are substantially identical in nature and design such that the description for one cam profile will suffice, and the corresponding components of the other cam profile will be designated with the same numerical characteristic having an &#34;a&#34; suffix. The cam profile 42 has a substantially radial step portion 46 which extends radially inwardly from the circumference 40 to intersect a recessed circumferential portion 48. The recessed circumferential portion is in intersecting relationship with a ramp portion 50 adjacent the step portion 46. The ramp portion 50 intersects the circumference 40 at 52. A second ramp portion 54 intersects both the circumferential portions 40 and 48 at a distance circumferentially displaced from the step 46 and ramp 50. As best seen in cam profile 44 a pair of end wall portions 56a and 58a extend between the circumferential portion 48a and the circumference 40, and between the ramp portion 50a and the circumference 40. 
     The cam member 12 has a centrally disposed opening 60 in which may be inserted a shaft, not shown, to support the cam 12 or alternatively provide a rotary input for the cam 12. As seen in FIG. 3 the cam 12 may be provided with and internally toothed diameter 62 which may also be utilized to provide an input drive to the rotary switch if desired. The input drive to the tooth portion 62 can be any of the well known type rotary drives such as high reduction types through the use of a small diameter pinion gear or an orbiting type gear which has slightly less teeth than the gear portion 62. These types of drives and others which are well known in the art may be used to provide the rotary input to the switch 10 depending on the particular nature of the device in which the switch is used. 
     As can be seen, in the position shown in FIG. 2, the cam follower 36 is aligned with the stepped portion 46a. Likewise the cam follower 38 is aligned with the step portion 46. When the cam 12 is rotated in the direction of arrow A, the cam follower 36 will remain in contact with the circumferential surface 40 until the step portion 46a is reached. At that time the spring action of arm 24 will cause the follower 36 to move radially inwardly into abutting relationship with the surface 48a. The steps 46 and 46a are angled to permit the slight rotation of the spring arms 24 and 26 relative to the base 20 caused by their inward movement. During this motion the electrical contact 28 will become disengaged from the contact member 16 thus opening the switch formed by contact 28 and terminal 16. In particular applications, such as antenna actuators, the source causing rotation of the cam 12 will be disconnected from electrical power upon opening of contacts 16 and 28, thereby stopping rotation of the cam 12 with the contacts 16 and 28 in the open position while the contacts 18 and 30 remain in the closed position. The switch is preferably used in a system wherein the reversible type drive is utilized. For example, the switch can be used in a conventional antenna actuator system wherein the up-down actuation of the antenna is signalled by a switch normally located in the radio circuit and a power disconnect switch, such as switch 10 described here, positioned between the power source and the actuator, and wherein the cam 12 is driven by the antenna drive motor at such a rate that upon reaching the fully extended or fully retracted position either switch contacts 16 and 28 or 18 and 30 will be opened to prevent further operation of the motor until the radio control switch is operated again. 
     Assuming that the switch contacts 16 and 28 are now open and the cam follower 36 is resting on surface 48a and further assuming that the drive system for the cam 12 is operated in reverse direction, the following will occur: as the cam 12 begins to rotate in a direction opposite to arrow A the cam follower 36 having a beveled portion 64 will abut the radial surface of cam 46a thereby forcing the spring arm 32 to be moved in the direction of arrow B such that the cam follower 36 will be aligned with the ramp 50a. The cam follower 36 will of course be maintained in alignment with ramp 50a due to the presence of end wall 58a until the circumferential surface 40 is reached at which time the spring arm 32 will move in the direction opposite to arrow B and become realigned with the step 46a. During the movement of spring arm 32, the spring arm 24 remains aligned vertically with the electrical contact 16 such that, upon the movement of the spring arm 24 towards the top terminal 16, the contact 28 undergoes a wiping action due to upward movement of the spring arm 24 and the bending which is accompanied with the spring force in arm 24. Thus on each closing of the switch contact there is a slight rocking motion of the contact points which maintains the good electrical contact. As the cam 12 continues to rotate in a direction opposite to arrow A the cam follower 38 will eventually come across the step portion 46 such that the cam follower will be forced into contact with the surface 48 through the spring action in arm 26 thus opening the electrical switch provided by contact 30 and terminal 18. At this time the electric motor driving the cam 12 will cease operation in a manner described above. 
     If the cam 12 is then rotated in the direction of arrow A, the bevel surface 66 on cam follower 38 will abut the radial surface of step 46, thereby moving the spring arm 34 downwardly as seen in FIG. 2, until alignment with ramp 50 is attained at which time the spring arm 26 will be forced upwardly toward the contact terminal 18 until the circumferential surface 40 is reached by the cam follower 38 and at which time the switch contact 30 and terminal 18 are in electrical contact and the cam follower 38 becomes aligned with step 46. If, for some reason, the cam 12 should continue to rotate after the switch contacts are opened and assuming the cam is rotating in the direction of arrow A, the follower 36 will engage the ramp 54a which will move the spring arm 24 upwardly as seen in FIG. 1 until the circumferential surface 40 is reached and the electrical contacts will be closed. The cam of course will then continue to operate and until the complete rotary movement had occurred at which time the cam follower 36 would again drop off the step 46a and open the switch contacts, this process would of course repeat in either direction of rotation until the motor rotating the cam 12 came to rest. 
     Obviously many modifications and variations of the present invention are possible in light of the above teaching. It is therefore to be understood, that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.