GB2071329A - Displacement transducer - Google Patents

Abstract

The transducer is a potentiometer constructed for fast relative movement of wiper (7) and cylindrical former. The wiper is annular and has three spring-loaded contacts with the windings, which are disposed on the former. Owing to the fact that the annular wiper is clamped tightly to the former by the spring-loaded contacts, it does not jump off the windings even at relatively high displacement velocities. <IMAGE>

Description

SPECIFICATION Displacement transducers This invention relates to displacement transducers.

In the measurement of displacement which occurs rapidly, such as may occur when a projectile impacts upon a member or surface, a problem is to measure the displacement in the very short time in which it occurs. One method of measuring these displacements is to use a potentiometer, in such a method the wiper and windings of the potentiometer are attached to different parts of the body to be impacted, which parts move relatively owing to the impact.

A problem with potentiometers used for this purpose is that owing to the rapid displacements involved, the wiper tends to jump off the windings which are carried on a former. Consequently, erroneous results can be obtained using potentiometers. It has been proposed to use a leaf spring to bias the wiper onto the former and windings. Unfortunately, even with a leaf spring according to this proposal, the wiper still tends to jump off causing misleading results to be given.

An object of the present invention is to provide a displacement transducer which tends to overcome the problem mentioned above.

According to the present invention, a displacement transducer comprises a hollow cylindrical former upon which electrical windings may be made, an annular wiper, and positive contact means between the annular wiper and the windings on the cylindrical former.

Preferably, the positive contact means comprises spring-loaded point contacts.

Advantageously, the point contacts are disposed around the circumference of the annular wiper.

Preferably, the ends of the windings pass into the former. The annular wiper may comprise an inner contact surface of low friction material.

An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is an elevation of a former, Figure 2 is an elevation of a wiper, Figure 3 shows a detail of Figure 2, and Figure 4 is a section of 111-Ill in Figure 2.

Reference is made firstly to Figure 1, in which a former for a potentiometer is generally indicated by 1. The former contains a central bore 2, which bore is widened at one end as shown to the left of the Figure and indicated at 3. This widening is to facilitate attachment of the former 1 to a body under investigation (which body is not shown). A hole 4 is drilled into the wall of the former so that a wire for winding around the former may be allowed to pass into the bore 2 in the former. A counterbore 5 is provided to the right of the former for a similar purpose. It will be appreciated that the two ends of the wire winding are therefore arranged to the right of the former without causing any unevenness of windings to occur.

Reference is now directed to Figure 2, in which an annular wiper for the former of Figure 1 is generally indicated by 7. The wiper 7 contains a number of holes 8 for carrying positive contact means to be described below.

Reference is now directed to Figure 4, wherein the wiper may be seen in more detail. The wiper comprises an alloy body 9, a plastic-type outer sleeve 10 and an inner bush 1 The inner bush 11 is of a material of low friction co-efficient, for example of PTFE. The positive contact means for insertion into the holes 8 comprises a contact member 12, a spring for biasing the member 13 and a screw 14 for exerting the requisite pressure on a spring. In Figure 3 the contact member may be seen in more detail.

The contact member 12 comprises a generally cylindrical body having a taper at one end thereof, which ensures good contact between the member 12 and the windings (not shown).

In operation, the former 1 is attached to one part of a body and the wiper 2 to another part of the body (which body is not shown).

Alternatively, the former 1 may be attached to one body and the wiper to another body which are going to experience relative displacement (neither of which bodies are shown). Rapid relative movement of the wiper 7 and former 1 are caused by a projectile impacting upon either the parts of a single body of the 2 bodies previously mentioned to cause a rapid relative displacement. Such a projectile impact may occur, for example, when a fast-moving member strikes a fixed member.

Owing to the fact that the annular member is clamped tightly to the former by virtue of the positive contact means described above, the annular member does not jump off the windings of a former, even at relatively high displacement velocities. Fast relative movement is aided by the low friction bush 1 There is no discontinuity in the windings on the former caused by the ends of the wire extending above the surface of the remainder of the windings.

From the foregoing, it will be apparent that the present invention provides a displacement transducer, which is able to give an accurate reading at relatively high speeds of the displacement between a potentiometer former and a potentiometer wiper.

1. A displacement transducer comprising a hollow cylindrical former upon which electrical windings may be made, an annular wiper and positive contact means between the annular wiper and the windings on the cylindrical former.

2. A displacement transducer as claimed in Claim 1, in which the positive contact means comprises spring-loaded point contacts.

3. A displacement transducer as clairned in Claim 2, in which the point contacts are disposed around the circumference of the annular wiper.

4. A displacement transducer as claimed in Claim 1, in which the ends of the windings pass into the former.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Displacement transducers This invention relates to displacement transducers. In the measurement of displacement which occurs rapidly, such as may occur when a projectile impacts upon a member or surface, a problem is to measure the displacement in the very short time in which it occurs. One method of measuring these displacements is to use a potentiometer, in such a method the wiper and windings of the potentiometer are attached to different parts of the body to be impacted, which parts move relatively owing to the impact. A problem with potentiometers used for this purpose is that owing to the rapid displacements involved, the wiper tends to jump off the windings which are carried on a former. Consequently, erroneous results can be obtained using potentiometers. It has been proposed to use a leaf spring to bias the wiper onto the former and windings. Unfortunately, even with a leaf spring according to this proposal, the wiper still tends to jump off causing misleading results to be given. An object of the present invention is to provide a displacement transducer which tends to overcome the problem mentioned above. According to the present invention, a displacement transducer comprises a hollow cylindrical former upon which electrical windings may be made, an annular wiper, and positive contact means between the annular wiper and the windings on the cylindrical former. Preferably, the positive contact means comprises spring-loaded point contacts. Advantageously, the point contacts are disposed around the circumference of the annular wiper. Preferably, the ends of the windings pass into the former. The annular wiper may comprise an inner contact surface of low friction material. An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is an elevation of a former, Figure 2 is an elevation of a wiper, Figure 3 shows a detail of Figure 2, and Figure 4 is a section of 111-Ill in Figure 2. Reference is made firstly to Figure 1, in which a former for a potentiometer is generally indicated by 1. The former contains a central bore 2, which bore is widened at one end as shown to the left of the Figure and indicated at 3. This widening is to facilitate attachment of the former 1 to a body under investigation (which body is not shown). A hole 4 is drilled into the wall of the former so that a wire for winding around the former may be allowed to pass into the bore 2 in the former. A counterbore 5 is provided to the right of the former for a similar purpose. It will be appreciated that the two ends of the wire winding are therefore arranged to the right of the former without causing any unevenness of windings to occur. Reference is now directed to Figure 2, in which an annular wiper for the former of Figure 1 is generally indicated by 7. The wiper 7 contains a number of holes 8 for carrying positive contact means to be described below. Reference is now directed to Figure 4, wherein the wiper may be seen in more detail. The wiper comprises an alloy body 9, a plastic-type outer sleeve 10 and an inner bush 1 The inner bush 11 is of a material of low friction co-efficient, for example of PTFE. The positive contact means for insertion into the holes 8 comprises a contact member 12, a spring for biasing the member 13 and a screw 14 for exerting the requisite pressure on a spring. In Figure 3 the contact member may be seen in more detail. The contact member 12 comprises a generally cylindrical body having a taper at one end thereof, which ensures good contact between the member 12 and the windings (not shown). In operation, the former 1 is attached to one part of a body and the wiper 2 to another part of the body (which body is not shown). Alternatively, the former 1 may be attached to one body and the wiper to another body which are going to experience relative displacement (neither of which bodies are shown). Rapid relative movement of the wiper 7 and former 1 are caused by a projectile impacting upon either the parts of a single body of the 2 bodies previously mentioned to cause a rapid relative displacement. Such a projectile impact may occur, for example, when a fast-moving member strikes a fixed member. Owing to the fact that the annular member is clamped tightly to the former by virtue of the positive contact means described above, the annular member does not jump off the windings of a former, even at relatively high displacement velocities. Fast relative movement is aided by the low friction bush 1 There is no discontinuity in the windings on the former caused by the ends of the wire extending above the surface of the remainder of the windings. From the foregoing, it will be apparent that the present invention provides a displacement transducer, which is able to give an accurate reading at relatively high speeds of the displacement between a potentiometer former and a potentiometer wiper. CLAIMS

1. A displacement transducer comprising a hollow cylindrical former upon which electrical windings may be made, an annular wiper and positive contact means between the annular wiper and the windings on the cylindrical former.

2. A displacement transducer as claimed in Claim 1, in which the positive contact means comprises spring-loaded point contacts.

3. A displacement transducer as clairned in Claim 2, in which the point contacts are disposed around the circumference of the annular wiper.

4. A displacement transducer as claimed in Claim 1, in which the ends of the windings pass into the former.

5. A displacement transducer as claimed in Claim 1, in which the annular wiper comprises an inner contact surface of low friction material.

6. A displacement transducer substantially as herein before described and as shown in the accompanying drawings.