US3440366A

US3440366A - Telephone switchhook mechanism

Info

Publication number: US3440366A
Application number: US518645A
Authority: US
Inventors: John L Samios
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1966-01-04
Filing date: 1966-01-04
Publication date: 1969-04-22
Anticipated expiration: 1986-04-22

Description

A ril 22, 1969 J. SAMIOS TELEPHONE SWITCHHOOK MECHANISM Sheet Filed Jan. 4, 1966 TORQUE 0 0?. fl

//VVENTOR J. L. SAM/05 ATTORNEY APril 22, 1969. J. SAMIOS 3,440,366

TELEPHONE SWITCHHOOK MECHANISM Filed Jan. 4, 1966 Sheet 3 0f 2 FIGS United States Patent Office 3,440,366 Patented Apr. 22, 1969 US. Cl. 179-464 Claims ABSTRACT OF THE DISCLOSURE In a telephone switchhook two springs are connected on opposite sides of the lever mechanisms pivot axis, and so anchored and biased that the net spring rate is negative. The contacts advantageously are closed with an increasing spring force, andthe lever-bearing reaction can be reduced toward zero.

This invention relates to telephone switchhook mechanisms and in particular to a mechanism of this type having improved dynamic action at hang-up.

Telephone switchhooks typically consist of a contact spring pile-up actuated by a system of levers. The pileup has two operational modes, corresponding to the onhook and off-hook positions of the lever system. Lever action is obtained normally through a pivoting movement about an axis. When not in use, the associated telephone handset is placed in some kind of cradle which includes a mechanism for applying all or part of the handset weight to the lever system to place and retain it in the on-hook position. When the handset weight is withdrawn, the lever system is pivoted back to its off-hook position by a switchhook biasing spring. The spring is usually a single helix that applies an increasing restorative force to the lever system as it is moved from off-to-on-hook.

This switchhook structure has certain inherent weaknesses that under some conditions create troublesome problems. For example, as the restorative force upon the lever system varies, an equal and opposite bearing reaction occurs at the lever pivot point. The existence of frictional reactive forces at the pivot point increases the chances of its binding and causing a malfunction of the contact spring pile-up. Furthermore, in the on-hook position, the torque exerted by the biasing spring is at a maximum, which increases the chance of contact bounce or chatter occurring in the spring pile-up upon hang-up.

There are also occasions when the combined torque exerted by the contact spring pile-up and the frictional torques are relatively large with respect to the torque exerted by the handset. The apparent remedy of using a weaker biasing spring, however, is unsound because it introduces a risk of pile-up malfunction in the off-hook mode. The case presents a design dilemma.

Additionally, with the above-described switchhook structure, the handset weight is critical in order to produce the work necessary to return the lever system to its onhook mode. If a lighter handset were desired, some compensation normally would be necessary within the lever system, e.g., a lighter biasing spring, or a larger lever arm. Either approach raises further problems, however. Lighter springing increases the risk of contact chatter; and larger lever arms require more space and involve more travel for some external part of the lever system.

Accordingly, one object of the invention is to lessen the likelihood of contact chatter in a telephone switchhook mechanism.

Another object of the invention is to reduce or eliminate the reactive bearing forces at the lever pivot point in such a mechanism.

A further object of the invention is to reduce the travel of the plunger or lever member, without risking contact spring malfunction or increasing bearing forces.

These and other objects are achieved in accordance with the invention by a novel telephone switchhook in which two resilient members are connected to the lever mechanism on opposite sides of its pivot axis, and so anchored and biased that the net spring rate is negative; and by adjusting the spring forces to compensate for lever or cradle weight, the bearing reaction approaches zero for useful displacements of the lever.

Pursuant to one aspect of the invention, the resilient members are two extension springs which oppose each other so that the reactive bearing forces cancel one another. Alternatively, by adjusting the relative positions of the springs and their spacing from the bearings, the bearing friction can be varied to control where needed the degree of friction damping.

The term negative spring rate in the sense herein used means that the sum of the torques applied to the pivot axis is less in the on-hook mode than in the off-hook mode. Thus, less handset mass is required to transfer the contact pile-up reliably to its on-hook mode. At the same time, more force is available to place the pile-up in its off-hook mode, resulting in more positive action. This is achieved in accordance with the inventive concept without incurring added bearing reactive forces.

Additionally, by positioning the biasing spring to introduce a controlled amount of bearing friction damping, the cradle velocity as it approaches off-hook may be reduced and rebound energy is absorbed. The arrangement provides fully adequate torque to place the switchhook in its off-hook mode for even the worst condition, yet essentially eliminates excessive rebound at either extreme of lever travel. The invention accordingly overcomes the problem of adequate contact operation caused by too little biasing; as well as the problem of contact chatter, caused by too much. i

A principal feature of the invention, therefore, resides in the use of two biasing members fastened from opposite sides of the switchhook lever pivot axis to opposite olfcenter portions of the lever, which substantially cancel each others bearing reaction.

Another feature of the invention involves the use of two biasing springs so mounted with respect to the switchhook lever that a greater biasing force is applied to the lever in its olf-hook mode than in its on-hook mode.

In the drawing:

FIG. 1 represents an arm-type switchhook mechanism representative of the prior art;

FIG. 2 is a schematic drawing showing the inventive principle employed in an arm-type switchhook;

FIGS. 3 and 4 are schematics showing action of forces in a switchhook with a dual return spring;

FIG. 5 is a schematic showing analysis of forces in a single return spring switchhook vs. angular displacement thereof; and

FIG. 6 is a plot of torque vs. angular displacement in a switchhook.

FIG. 1 shows a telephone desk set including a housing 1 in which is mounted an arm-type switchhook assembly. This switchhook assembly comprises a unitary handset cradle-switchhook lever 2 typically consisting of two cradle arms 3, 4, connecting bar 5 and bearings 6, 7. A contact spring pile-up 8 is actuated by a link 9 connected to lever 2 at some point such as plate 10. The switchhook is supported in mounting bracket 11 which fastens rigidly to a fixture (not shown) within housing 1. Bracket 11 includes a pair of opposed stationary support arms 12 which support a pivot rod 13 in bearing holes. Bearings 6, 7, of the switchhook lever 2 ride on rod 13 inwardly of arms 12.

An extension 14 of support arm 12 serves as a fixed mount for a biasing spring 15, the other end of which is fastened to an extension 16 of plate 10. Pivotal movement of lever 2 is limited by a set of fixed stops (not shown) between which plate 10 can move. When an associated telephone handset (not shown) is removed from arms 3, 4, the switchhook is placed in its off-hook mode by contraction of spring 15. Replacing the handset onto arms 3, 4, depresses the lever 2, causing it to pivot about rod 13 and extending spring 15.

It can be seen that the entire force of spring 15 is applied to the bearing holes of arm 12. As mentioned, this is a source of potential wear and binding, since the spring force is in the order of six pounds. If it were required to convert the switchhook assembly of FIG. 1 from one having a positive spring rate as shown to one having a negative rate, it would be necessary to employ a still stronger spring. The wear and chances of binding at the bearing points would be greatly increased, however, since the bearing reaction would be increased. Also, the energy dissipated in friction work would exceed the quantity of energy stored in the return spring, causing a pile-up malfunction.

Pursuant to the invention, a net negative spring rate may be achieved while actually reducing or eliminating the bearing reactance, by employing two springs in the manner shown in FIG. 2. A straight link 20 rotatably mounted with respect to pivot rod 13 is rigidly secured to arm 3 of switchhook lever 2 so that they rotate together. Link 20 comprises first and second legs 21, 22, which are equal in length. Legs 21, 22 include

projections

23, 24, respectively. Two

helical springs

25, 26, are connected to

projections

23, 24. Spring 25 is anchored to the upper extension 14 of stationary support arm 12, and spring 26 is anchored to a lower extension 16 of stationary support arm 12. Link 20 and springs 25, 26, are aligned so that they fall in substantially the same plane, and this plane is perpendicular to the pivot axis 13.

FIG. 2 shows the spring alignment when the switchhook is on-hook. This is depicted schematically in FIG. 3, in which spring 25 exerts a force F through a torque arm 1' and spring 26 exerts a force F through a torque arm r FIG. 4 shows schematically the spring alignment in the off-hook condition. The torque arms r r have increased in length to r r The spring forces F F have decreased to F F because the spring contracted as the link 20 rotated. The spring alignment may be selected to that as the switchhook moves from on-hook to off-hook, the torque arms r r increase at a rate that exceeds the rate of decrease of the spring forces F F resulting in a net increase in torque. This provides more biasing force for the switchhook in the off-hook mode. Additionally, if the torque arms are made equal at all times and if F =F then the bearing reactance from these forces is substantially zero. The total bearing friction is thus reduced very considerably.

FIGS. 5 and 6 are aids in analyzing for purposes of comparison the dynamic action of the l-spring switchhook of FIG. 1. The spring 15 may be considered as an extensible link of a three bar linkage in which the other two links (shown for illustration as 18, 19, in FIG. 5) are the stationary mounting bracket 11 and the lever-

plate assembly

2, 10, 16. Link 18 is rigid and stationary; link 19 is rigid and rotative about axis 13; and spring 15 is extensible and rotative about pivot point 14 on bracket 11. The angle is a useful linkage parameter and is determined by the distance between the line of action of spring 15 and axis 13. The angle is the supplement of 0.

The torque exerted upon lever 2 varies with the changes in 0. FIG. 6 shows the approximate torque-angular displacement function for an idealized system. If an operating region (Afll) of positive slope is chosen, the torque change from off-hook to on-hook (AT1) is an increase. If an operating region (AB2) of negative slope is chosen, the torque change (Av-2) is a decrease. A similar curve involving the same considerations may be constructed for the two-spring switchhook of the instant invention.

A given switchhook stroke can be selected between any two points on the FIG. 6 curve. If a region of negative slope is desired then the spring force must be increased siza bly to enable operation in this region. In a l-spring system this will result in considerable added bearing friction. However, the use of two springs in accordance with the invention, as shown in FIGS. 2-4, avoids the friction load penalty, since they may be arranged to cancel each others resultant load on the bearings. Further, it is possible with the instant invention to devise a switchhook with reduced stroke (A5) while maintaining, or increasing, the negative change in torque (AT) because this arrangement permits operation in the region close to a 3 angle of where slope of the curve is most negative.

The springs may also be positioned to introduce a controlled amount of bearing friction to reduce contact chatter. This may be achieved by offsetting either or both

springs

25, 26 so that they are not in the same plane; or by choosing springs of unequal force.

Although the inventive concept has been described in conjunction with a single specific type of switchhookhandset system, it will be obvious to persons skilled in the art that the invention is equally applicable to any type of switchook that involves a pivoted lever system relying upon the weight of the handset to place the set on-hook.

Furthermore, various changes and modifications to the inventive concept herein illustrated may occur to persons skilled in the art, and it is to be expressly understood that all such changes and modifications are intended to be included within the spirit and the scope of the invention as defined in the claims to follow.

What is claimed is:

1. In a telephone switchook including a contact spring pile-up having an on-hook mode and an off-hook mode, means including a pivotable lever responsive to pivoting thereof between a first and a second position for switching the contact spring pile-up between its respective modes, and bearing means for pivotally mounting the lever, the improvement comprising, in combination,

(a) resilient means other than said spring pile-up for applying to the lever a first force when in its first position and a second larger force when in its second position; and

(b) means including said resilient means for maintaining upon said bearing means a net resultant force substantially equal to zero.

2. In a telephone switchhook including a contact spring pile-up having an on-hook mode and an off-hook mode, a pivot axis, bearing means for supporting said pivot axis, a lever mounted for pivotal movement about said pivot axis and means responsive to the pivoting of said lever between a first and a second position for switching the contact spring pile-up between its respective modes, the improvement comprising, in combination,

(a) means including first and second biasing springs responsive to pivotal movement of said lever for applying to said lever a varying torsional force, said torsional force being least when the contact spring pile-up is in its on-hook mode and said torsional force being greatest when the contact spring pile-up is in its off-hook mode;

(b) means including said first biasing spring for applying to said bearing means a first force; and

(c) means including said second biasing spring for applying to the bearing means a second force, said first and second forces being substantially equal in magnitude and opposite in direction, whereby the net reactive force of the spring forces upon the bearing means is substantially zero.

3. A switchhook in accordance with claim 2 wherein the first biasing spring is mounted on one side of the pivot axis and the second biasing spring is mounted on the opposite side of the lever.

4. A switchhook in accordance with claim 3 wherein the force vectors of said first and second forces occupy 5 6 the same plane, and said plane is substantially perpendic- References Cited ular to the lever pivot axis. UNITED STATES PATENTS 5. A switchhook in ac cordance with claim 2 whereln 3,027,432 3/1962 Jordan et a1. sa1d first and second blaslng springs each have an end anchored to a stationary point on said switchhook and 5 KA L A Primary Examiner, vherein said switchhoolt further inclndes means for vary- L RAY, Assistant Examiner. mg the locations of said anchor polnts, thereby to control the reactive force of said biasing springs upon the US. Cl. X.R. bearing means. 200153