Switch Actuating Mechanism

Abstract

A pushbutton switch for holding a microswitch in its open position for a period of time less than a preselected duration. A plunger is slidably mounted within a cylindrical pushbutton and is urged out of said pushbutton by a helical spring. Vent holes and bleed paths are formed in said plunger and combine with an O-ring positioned between the plunger and the interior of the pushbutton to provide pneumatic damping to retard the movement of the plunger out of the pushbutton.

Description

BACKGROUND OF THE INVENTION

This invention relates to a mechanism for releasing a biased switch contact unit actuator and more particularly to such a mechanism for releasing a biased switch contact actuator for a duration not exceeding a predetermined time limit.

Such a mechanism may be advantageously utilized in a telephone unit as part of a pushbutton switch of the type commonly mounted on a telephone subset. The mechanism is useful, for example, during a telephone conversation when one of the parties to the call may desire to speak with an operator without terminating said call. With common telephone subsets the attention of the operator can usually be attracted by rapidly operating the cradle switch. However, there is the danger, in this method of attracting the operator's attention, that the cradle switch will be accidentally depressed for a time duration exceeding the hold time of the telephone exchange relay, and in this event the call will be inadvertently terminated. The instant mechanism may be utilized to prevent such inadvertent termination.

SUMMARY OF THE INVENTION

Therefore, the main object of this invention is to provide a mechanism for holding a biased switch in a position other than its biased position for a period of time not exceeding a pre-selected duration.

According to the present invention there is provided a timer apparatus for holding a biased switch in a position other than its biased position for a period of time not exceeding a pre-selected duration comprising support means having an aperture formed therein, contact means having a cavity formed therein, said contact means mounted to said slide in said aperture, plunger means for controlling the position of a biased switch mounted in the cavity of said contact means and adapted to slide therein, spring means positioned in said cavity between the closed end of said cavity and said plunger means for urging said plunger means out of said cavity, and damper means extending between the exterior of said timer apparatus and said cavity for retarding the movement of said plunger out of said cavity.

BRIEF DESCRIPTION OF THE DRAWINGS

The single drawing is a sectional view illustrating the subject mechanism and its position relative to a biased switch.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the single FIGURE in the case, there is shown part of the body of a telephone subset which forms a housing 1 in which is located a pushbutton contact 2 in the form of a hollow cylinder, that is, having a cavity 3 formed therein, having one closed end 4 and an outwardly extending flange 5 at the opposite end. The pushbutton is capable of sliding movement through the housing in an axial direction. The flange 5 cooperates with the underside 6 of the housing 1 to provide an end-stop for limiting the extent of travel of the pushbutton out of the housing.

A cylindrical plunger 7 is positioned in said cavity and is adapted for sliding movement in an axial direction in and out of the interior 3 of the pushbutton. Plunger 7 is however urged out of the cavity 3 by a compression spring 8 which is compressed between the upper surface 9 of plunger 7 and the closed end 4 of the pushbutton. The plunger 7 is provided with a groove 10 in its side wall which accommodates an O-ring 11. The width of the groove 10 is greater than the O-ring 11 so that the O-ring is capable of restricted movement in an axial direction. The depth of the groove 10 is also made greater than the width of the O-ring 11 so that there is an annular space 12 between the inside of the O-ring and the bottom of the groove. Below the level of the groove plunger 7 fits snugly in the pushbutton but above the groove the side wall of the plunger is relieved to provide a clearance 13 between the plunger and the interior wall of pushbutton 2. Two vent holes 14 provide an air passageway from the bottom surface 15 of the plunger to the bottom of groove 10 in the plunger side wall. There is also a bleed hole 16 axially extending the length of the plunger.

When O-ring 11 rests against the lower side wall of groove 10 in plunger 11 (i.e., the outer side wall), and not against the upper side wall (i.e., the inner side wall) as is illustrated in the drawing, air is freely able to enter or leave the interior of pushbutton 2 via vent holes 14, groove 10, and clearance 13 between the part of the plunger above groove 10 and the adjacent part of the interior side wall of the pushbutton. However, if O-ring 11 is carried up to rest against the upper side wall of the groove, as is the condition shown in the drawing, this air passage is effectively sealed by the O-ring and air can only enter or leave the interior of the pushbutton via bleed hole 16.

The assembly thus far described with reference to the drawing is mounted in relation to a microswitch 17 such that its actuator 18 is depressed by plunger 7 when the pushbutton 2 is at rest.

With the pushbutton 2 at rest actuator 18 is depressed by the compression force of the spring 8 acting through plunger 7. The reaction to this force upon the actuator 18 is transmitted through the spring 8, the pushbutton 2, and its flange 5 to the underside 6 of the housing 1. In order for this force to depress the actuator 18 it must of course be greater than the actuator restoring force provided by the internal spring biasing mechanism of the microswitch 17.

When the pushbutton 2 is depressed plunger 7 is unable to travel down with the pushbutton as it is held back by actuator 18 which is itself fully depressed. Therefore the plunger begins to slide further into the pushbutton cavity 3 and thereby causes O-ring 11 to come to rest against the lower side wall of the groove in which it is accommodated.

As the pushbutton is further depressed the volume of the air space inside the pushbutton is reduced, but becomes the O-ring is by now resting against the lower side wall of groove 10 in plunger 7, the air pressure in this shrinking volume is not significantly increased because air is able freely to escape via the vent holes 14.

When the pushbutton is released spring 8 will tend to force the pushbutton and plunger apart. This will cause the volume of the air space inside the pushbutton to be increased. At first the pressure of air in this volume is not significantly reduced because air is able freely to enter the cavity 3 via the vent holes 14. Therefore, initially, the only force opposing that of the spring is that provided by friction between the pushbutton and the plunger and hence their initial movement apart will be relatively rapid. This initial movement will however carry O-ring 11 to rest against the upper wall of the groove in the plunger where it seals off the inrush of air. Thereafter air can only enter cavity 3 of pushbutton 2 via bleed hole 16, and hence further movement apart of the pushbutton and plunger creates a partial vacuum inside the pushbutton which provides a damping force retarding separation of the pushbutton and plunger.

Thus, initially, spring 8 will expand relatively rapidly but after a short distance its rate of expansion will be pneumatically damped. For the majority of the time that the spring is expanding flange 5 will not abut the underside 6 of the housing 1, and hence there will be nothing, except frictional forces and the mass of the pushbutton, spring and plunger, tending to oppose the restoring force provided to actuator 18 by the internal mechanism of microswitch 17. Therefore once the pushbutton is released the microswitch actuator 18 is also released and will stay released until such time as flange 5 meets the underside 6 of the housing 1, whereupon continued expansion of the spring will cause actuator 18 to once again be depressed.

If pushbutton 2 is not fully depressed before being released then less air will be required to enter cavity 3 via bleed hole 16 before pushbutton flange 5 abuts the underside 6 of the housing, and in consequence thereof the release time of actuator 18 is shortened. Similarly, since the reactuation of microswitch 17 is only prevented while pushbutton 2 is still able to rise after being depressed, the effect of impeding the pushbutton in its return to its rest position can only shorten the duration during which actuator 18 is released. Clearly the duration of the release of microswitch 17 is unaffected by the duration for which pushbutton 2 is held down. Therefore with this mechanism the actuator 18 of microswitch 17 can be released only for a duration which does not exceed a predetermined or selected limit. This predetermined limit is the duration of actuator release which occurs when pushbutton 2 is quickly and completely released after being fully depressed and is selected to be short enough so that a call on the telephone subset into which this invention is incorporated will not be unintentionally terminated.

It is to be understood that the foregoing description of specific examples of this invention is made by way of example only and is not to be considered as a limitation on its scope.

Claims

I Claim:

1. Timer apparatus for holding a biased switch in a position other than its biased position for a period of time not exceeding a preselected duration comprising:

support means having an aperture formed therein;

contact means having a cylindrical cavity formed therein, said contact means mounted to slide in said aperture;

cylindrically shaped plunger means for controlling the position of a biased switch mounted in the cavity of said contact means and adapted to slide therein, said plunger means having a groove formed in the side wall thereof, with the diameter of said plunger means below said groove being equal to that of said cavity and the diameter of said plunger means above said groove being less than that of said cavity;

spring means positioned in said cavity between the closed end of said cavity and said plunger means for urging said plunger means out of said cavity; and

damper means extending between the exterior of said timer apparatus and said cavity for retarding the movement of said plunger out of said cavity.

2. Timer apparatus for holding a biased switch in a position, according to claim 1, wherein said damper means comprises:

at least one vent hole in said plunger forming a first fluid path from said exterior to said cavity via said groove; and

an O-ring, having a width less than the width of said groove, positioned in said groove and adapted to move to a first axial position therein to open said path in response to the movement of said plunger in said cavity, and to a second axial position therein to close said path in response to the movement of said plunger out of said cavity.

3. Timer apparatus for holding a biased switch in a position, according to claim 2, wherein said damper means further comprises a bleed hole formed in said plunger and extending axially therethrough between said exterior and said cavity.

4. Timer apparatus for holding a biased switch in a position, according to claim 3, wherein said contact means further comprises:

an annular flange at the end thereof adjacent the opening of said cavity,

said flange positioned to be brought into contact with said support means to limit the travel of said contact means.