GB2243727A - Contact probe - Google Patents

Abstract

A contact probe for use in a harness tester for testing an electric conductivity in an electric wiring harness, comprises a tubular sheath (1) having an annular retainer (4) defined at a generally intermediate portion thereof so as to protrude radially inwardly thereof; a plunger (3) accommodated within the tubular sheath for axial movement between projected (Figure 5) and retracted position and having a plunger segment (3a) defined therein and positioned within the tubular sheath and between the annular retainer and a closed end of the tubular sheath; and a biasing spring (9) interposed between the closed end of the tubular sheath and the plunger segment for urging the plunger to the projected position. A cushioning element in the form of a coil spring (20) or an elastic bushing is interposed between the annular retainer (4) and the plunger segment (3a) to avoid any possible abrupt contact of the plunger segment with the annular retainer in the event that the plunger once moved to the retracted positon is axially forceable thrust towards the projected position by the action of the biasing spring (9). <IMAGE>

Description

"CONTACT PROBE IN ELECTRIC CONDUCTIVITY TESTER" The present invention relates to a contact probe for use in a harness tester for testing an electric conductivity in an electric wiring harness.

In an automobile, for example, electric wires used to distribute electric power among numerous electrically operated devices are bound together into harnesses. Those electric wires bound together into the harnesses are generally known as wiring harnesses and are generally marked by means of colors for identification purpose. A single wiring harness generally comprises a number of electric wires and has at least one terminal connector at one end thereof. Each of the terminal connectors may comprise a molded connector casing having a plurality of terminal members equal in number to the number of the electric wires forming the wiring harness. The terminal members in the terminal connector or connectors may be in the form of either terminal pins or terminal sockets.

In one application, the electric wires forming the wiring harness may lead out from an electrically operated device and terminate in the terminal connector for connection with a different electrically operated device either directly or through another similar wiring harness having terminal connectors at its opposite ends.

In another application, at least two electrically operated devices may be connected with each other through a wiring harness having terminal connectors at its opposite ends. In this case, one or both of those electrically operated devices must have terminal members installed thereon in coaxial relationship with the terminal members in the associated terminal connector in the wiring harness.

To determine the presence or absence of an abnormality in the wiring harness, for example, that of a wiring breakage occurring in any one of the electric wires forming the wiring harness, the use has hitherto been made of a harness testing equipment which may comprises an electric testing instrument, which may include a visual and/or audio indicator, and a harness tester comprising a releasable connector holder for the support of the terminal connector and a probe assembly supported for movement relative to the connector holder in a direction close towards and away from the terminal connector.

The probe assembly includes a plurality of contact probes generally equal in number to the terminal members in the terminal connector and electrically connected with the electric testing instrument.

More specifically, with reference to Figs. 1 and 2 showing perspective views of the standard harness testing equipment and the harness tester, respectively, the electric testing instrument and the harness tester are generally identified by 40 and 50, respectively. So far shown therein, two harness testers 50 are employed as mounted fixedly on a support board B. Each harness tester 50 comprises a probe assembly 51, having a plurality of generally elongated contact probes 52 which are substantially permanently connected with the electric testing instrument 40, and a connector holder 53 for the support of a corresponding one of the opposite terminal connectors HC of one wiring harness H.

In testing the conductivity of the wiring harness as a whole, the opposite terminal connectors HC of the wiring harness H to be tested are mounted on the associated connector holders 53 with the terminal members aligned with the contact probes 52, and the probe assemblies 51 are then moved close towards the associated connector holders 53 so that the contact probes 52 can be brought into contact with the respective terminal members in the terminal connectors H on the connector holders 53. The testing instrument 40 can provide a visual and/or audio indication either when no abnormality is found in each of the electric wires HW in the wiring harness H or when an abnormality is found in at least one of the electric wires K in the wiring harness H.

The movement of the probe assembly 51 relative to the connector holder 53 in each harness tester 50 is carried out by manipulating a handle 54 pivotable between release and test positions.

It should be noted that the harness tester to which the present invention is applicable is not always limited to that shown in Figs. 1 and 2, but may be of a type disclosed in, for example, the Japanese Utility Model Publication No.

53-18545, published May 17, 1978; the Japanese Utility Model Publication No. 55-8221, published February 23, 1980; the Japanese Laid-open Patent Publication o. 60-140160, published July 25, 1985; and United States Patent o. 4,849,743 issued July 18, 1989.

In any event, each of the contact probes hitherto used in the harness tester is of a structure which will now be described with reference to Figs. 3 and 4 of the accompanying drawings, which respectively illustrate the contact probe in longitudinal sectional representation in different operative positions.

The illustrated contact probe 52 comprises a tubular sheath 1 of electrically conductive material having a rear end closed by a ball 2, a plunger 3 of electrically conductive material accommodated axially slidably within the tubular sheath 1 with a front end portion protruding outwardly from a front open end of the sheath 1. The tubular sheath 1 has a generally intermediate portion constricted radially inwardly so as to define an annular retainer 4 protruding a predetermined distance inwardly of the tubular sheath 1.

The plunger 3 is of a design having a rear end 5 reduced in diameter to define an annular spring seat 6 and also having a generally intermediate portion thereof reduced in diameter to provide a trunk 7, thereby leaving an annular abutment 8 opposite to the annular spring seat 6, said trunk 7 being of a diameter substantially equal to or slightly smaller than the minimum inner diameter of the tubular sheath 1 which is measured at the annular retainer 4. This plunger 3 slidably accommodated in the tubular sheath 1 is movable between a projected position, shown in Fig. 3, and a retracted position shown in Fig. 4 and is normally biased to the projected position by the action of a biasing spring 9 which is interposed between the spring seat 6 and the ball 2.With the plunger 3 so biased to the projected position, the annular abutment 8 confronting the annular retainer 4 is brought into engagement with the annular retainer 4.

As best shown in Fig. 4, the tubular sheath 1 having the plunger 3 accommodated therein is press-fitted into a sleeve 10 of electrically conductive material with the front open end thereof held substantially in flush with a corresponding front open end of the sleeve 10, while a rear end of said sleeve 10 is adapted to be electrically connected with the testing instrument 40 (Fig. 1).

Reference numeral 11 represents a contact element, formed integrally therewith or otherwise connected thereto, for engagement with one of terminal members welded to the electric wires HW forming the wiring harness H to be tested.

As discussed with reference to Figs. 1 and 2, a plurality of the contact probes 52, each being of the construction shown in and described with reference to Figs. 3 and 4, are embedded in a molded block to provide the probe assembly 51 with the respective contact elements 11 situated exteriorly of the molded block. By way of example, where the harness tester 50 is of a type used with the terminal connector having two rows of a plurality of, for example, six, terminal members, the contact probes 52 molded in the molded block are arranged in two rows of the six probes.

During the actual conductivity testing, the probe assembly 51 is moved from the release position towards the test position, i.e., in a direction close to the terminal connector HC then retained by the connector holder 53. As the probe assembly 51 is moved towards the terminal connector HC, the contact elements 11 are brought into contact with the respective terminal members (one of which is shown by TM in Fig. 5) which are embedded in the connector casing, with the associated plungers 3 consequently moved from the projected positions towards the retracted positions against the respective biasing springs 9.

After the conductivity test, the probe assembly 51 is moved backwards to the release position in readiness for the next cycle of testing of another wiring harness with the terminal connector replaced with another terminal connector.

Apart from the specific structure of each contact probe, the terminal connector used in association with the wiring harness is currently miniaturized. As a result of the miniaturization, a cavity defined in the connector casing and into which the contact elements 11 of the probe assembly 51 are inserted during the conductivity testing is correspondingly reduced in size to an extent that one or some of the contact elements 11 may often entrapped undesirably by projections found inside or around the cavity. Once this occurs, the following problem may arise, which will be discussed with reference to the single contact probe 52.

When the contact element 11 is entrapped by a projection found in the vicinity of the cavity, the associated plunger 3 carrying such contact element 11 is considerably retracted inwardly of the tubular sheath 1 against the biasing spring 9 during the movement of the probe assembly from the release position towards the test position. A further push of the probe assembly close towards the terminal connector held by the connector holder may cause the contact element 11 to disengage from the projection. This disengagement of the contact element 11 from the projection allows the plunger 3 to abruptly move towards the projected position biased by the biasing spring 9, with the annular abutment 8 brought subsequently into abrupt contact with the annular retainer 4.

The abrupt contact of the annular abutment 8 with the annular retainer 4 imposes a shock on the tubular sheath 1 as a whole, causing the latter to be popped or thrusted a certain distance L axially outwardly from the sleeve 10 as indicated by the phantom line in Fig. 4. This popping action of the tubular sheath 1 under the influence of shock generated as a result of the abrupt contact of the annular abutment 8 with the annular retainer 4 destroys the position of the tubular sheath 1 relative to the sleeve 10 and, in turn, the position of the contact probe 52 relative to the molded block of the probe assembly, bringing about a problem that the harness conductivity test may give out an erroneous test result.

In the worst case it may happen, the popping action of the tubular sheath 1 may result in a separation of the tubular sheath 1 out from the sleeve 10 and, in such case, the harness conductivity test will no longer be performed.

Also, the prior art structure shown in Figs. 3 and 4 is such that the engagement of the annular abutment 8 with the annular retainer 4 defines the projected position for the plunger 3 while preventing the plunger 3 from being thrusted outwardly from the sleeve 10. In other words, the prior art structure employs a rigid support system for the support of the plunger, rigid in the sense that the plunger 3 can resist against an external pulling force which may be applied thereto.Specifically, after the conductivity test and in the event that one or some of the contact elements 11 is trapped by an obstruction present inside the connector housing during the separation of the terminal connector HC from the probe assembly, an attempt to forcibly pull the terminal connector HC away from the probe assembly with an external pulling force consequently acting on one or some of the contact elements 11, the plunger or plungers 3 associated with the contact element or elements 11 then trapped by the obstruction are susceptible to bending.

The present invention has been devised with a view to substantially eliminating the above discussed problems inherent in the prior art contact probe and is intended to provide an improved contact probe for use in a harness tester for testing an electric conductivity in an electric wiring harness, which employs a resilient support system for the plunger thereby to avoid any possible axial pop of the tubular sheath relative to the sleeve, thereby to ensure an accurate and reliable conductivity testing.

According to the present invention, the above described object can be advantageously accomplished by the provision of a cushioning element between the retainer in the tubular sheath and the annular abutment on the plunger.

Preferably, the cushioning element counteracting with the biasing spring interposed between the annular spring seat and a closed rear end of the tubular sheath may comprise a coil spring. Alternatively, the cushioning element may be employed in the form of a rubber or elastic piece.

According to the present invention, when the contact element 11 is entrapped by a projection found in the vicinity of the cavity in which the terminal members in the terminal connector are situated, and is subsequently disengaged therefrom, the annular abutment on the plunger will not be abruptly brought into contact with the annular retainer. This is because the cushioning element interposed between the retainer and the annular abutment serves to provide a cushioning effect to the movement of the plunger thereby to avoid any possible abrupt contact of the annular abutment with the retainer.

Accordingly, the abrupt disengagement of the contact element from the projection or any other obstruction is not followed by the abrupt axial thrust of the plunger and, therefore, the tubular sheath does not pop outwardly from the sleeve.

This and other objects and features of the present invention will become clear from the following description taken in conjunction with a preferred embodiment thereof with reference to the accompanying drawings, in which: Fig. 1 is a perspective view of the standard harness testing equipment; Fig. 2 is a perspective view, on an enlarged scale, showing one of the harness testers used in the harness testing equipment of Fig. 1; Figs. 3 and 4 are longitudinal sectional views, on a further enlarged scale, of one of the prior art contact probes used in the harness tester, which is shown in different operative positions, respectively; and Figs. 5 and 6 are views similar to Figs. 3 and 4, respectively, showing a contact probe designed according to the present invention.

Before the description of the preferred embodiment of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings.

As shown in Figs. 5 and 6, a contact probe 52 embodying the present invention is substantially identical with the prior art contact probe except that, in accordance with the present invention, a cushioning element identified by is interposed between the annular retainer 4 and the annular abutment 8 defined in a plunger segment 3a together with and in opposition to the annular spring seat 6. So far show, the cushioning element is employed in the form of a coil spring 20 which may be a compression spring. Instead of the use of the coil spring 20, an annular elastic bushing made of rubber or any other suitable resilient material may be employed.

In accordance with the present invention, the coil spring 20 should be of a type having a spring constant smaller than the spring constant of the biasing spring 9 such that, when and so long as the plunger 3 is held in the projected position as shown in Fig. 5, the coil spring 20 and the biasing spring 9 counterbalance with each other. In this condition, the coil spring 20 within the tubular sheath 1 is somewhat compressed axially inwardly between the retainer 4 and the annular abutment 8 of the plunger segment 3a to permit the plunger 3 to assume the projected position as shown in Fig. 5. Thus, it will readily be seen that the plunger 3 is movably supported within the tubular sheath 1 in a resilient support system.

It is to be noted that the foregoing description concerning the spring constant can be substantially equally applicable even where the cushioning elements employed in the form of an annular elastic bushing made of rubber or any other suitable resilient material singly or in combination with a coil spring.

When in use, the plunger 3 is moved from the projected position towards the retracted position as shown in Fig. 6 with the contact element 11 in abutment with the corresponding terminal member TM in the terminal connector HC (Fig. 2). At this time, the movement of the plunger 3 towards the retracted position causes the plunger segment 3a to move a distance away from the retainer 4, which distance may be greater than that in the prior art contact probe because of the intervention of the coil spring 20. To avoid any possible arbitrary motion of the coil spring 20 within a space delimited within the tubular sheath 1 and between the annular retainer 4 and the annular abutment 8, the coil spring 20 is preferred to have one end secured to either the annular retainer 4 or the annular abutment 8 when the plunger 3 is in the retracted position.

From the foregoing description, it has been made clear that, even when the contact element 11 is entrapped by a projection found in the vicinity of the cavity and is subsequently abruptly disengaged therefrom, the cushioning element effectively operates to avoid any possible abrupt contact of the annular abutment 8 with the annular retainer 4.

In other words, the cushioning element serves to retard the abrupt return motion of the plunger 3 back towards the projected position, absorbing an axial thrust acting on the plunger 3 to move the latter to the projected position.

Therefore, the popping action of the tubular sheath 1 relative to the sleeve 10 which would occur under the influence of shock generated as a result of the abrupt contact of the annular abutment 8 with the annular retainer 4 can be effectively and advantageously avoided.

The fact that the popping action of the tubular sheath is effectively avoided ensures that the plunger 3 is held at the projected position at all times unless no pushing force is applied t hereto and, therefore, no attendant worker is required to ascertain the position of the plunger and, hence, the contact element 11, each time the conductivity test is carried out.

In addition, because of the employment of the resilient support system for the plunger 3, the cushioning element is effective to absorb any possible undesirable pulling force applied externally to the plunger 3 thereby to avoid any possible damage to the contact probe as a whole and also a malfunctioning of the contact probe.

Although the present invention has been described in connection with the preferred embodiment thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. For example, in the practice of the present invention, the sleeve enclosing the tubular sheath need not be always necessary and the tubular sheath may be press-fitted into a corresponding hole defined in the molded block of the probe assembly.

Accordingly, such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.

Claims (5)

CLAIMS:

1. A contact probe for use in a harness tester for testing an electric conductivity in an electric wiring harness, which comprises: a tubular sheath having closed and opened ends opposite to each other, said tubular sheath having an annular retainer defined at a generally intermediate portion thereof so as to protrude radially inwardly thereof; a plunger accommodated within the tubular sheath for axial movement between projected and retracted positions, said plunger having a plunger segment defined therein and positioned within the tubular sheath and between the annular retainer and the closed end of the tubular sheath; a biasing spring interposed between the closed end of the tubular sheath and the plunger segment for urging the plunger to the projected position; and a cushioning element interposed between the annular retainer and the plunger segment and operable to avoid any possible abrupt contact of the plunger segment with the annular retainer in the event that the plunger once moved to the retracted position is axially thrusted towards the projected position by the action of the biasing spring.

2. The contact probe as claimed in Claim 1, wherein said cushioning element has a spring constant smaller than the spring constant of the biasing spring.

3. The contact probe as claimed in Claim 1, wherein said cushioning element is a coil spring.

4. The contact probe as claimed in Claim 2, wherein said coil spring has a spring element smaller than the spring constant of the biasing spring.

5. A contact probe substantially as hereinbefore described with reference to and as shown in any of Figures 5 and 6 of the accompanying drawings.