WO1994026005A1

WO1994026005A1 - Contact pressure transducer

Info

Publication number: WO1994026005A1
Application number: PCT/AU1994/000228
Authority: WO
Inventors: Andreas Helwig
Original assignee: Queensland Railways
Priority date: 1993-05-05
Filing date: 1994-05-05
Publication date: 1994-11-10

Abstract

A transducer (45) for measuring contact force pressure between a brush and commutator (52), the transducer (45) including a transducer block (46) made of a material having similar characteristics to the brush, a transducer head (47), a recess in a face (40) of the block (46) for receiving the head (47) and from which the head (47) projects so that it may contact the commutator (52) against which the block (46) may be biased. The block (46) has a passage (49) through which an electrical lead (48) extending from the head (47) may pass.

Description

TITLE CONTACTPRESSURETRANSDUCER FIELD OF THE INVENTION THIS INVENTION relates to a transducer for measuring contact face pressure between a brush and a commutator.

BACKGROUND OF THE INVENTION

The invention will be described by way of example with reference to DC traction machines. It should be appreciated that this is by way of example only and that the transducer of the invention may also be used in machines other than DC traction machines.

It is important for current transfer between the commutator and the brush, brush life and for current sharing between brushes of the same polarity that the brush spring tension be within a predetermined range, and that the spread of tension values within the traction motor be minimal. This allows for extended brush life and reduced maintenance and servicing. One known device for determining brush pressure was manufactured by the National Carbon Group in Holland and sold under the name Bintpres D5. This device had a transducer head which consisted of a strain gauge or the like coupled to a hand held monitor which provided a read out of pressure applied by a brush spring to the top of the brush. The transducer head was transposed between the spring and the brush head. The very placement of the head meant that an actual indication of the contact pressure between the brush and commutator was not obtained.

In any event, the Bintpres device did not yield repeatable results in that the transducer head could not be accurately and repeatably aligned relative to the spring and the brush. The transducer head included a piezoelectric transducer and repeatable application of force at a predetermined location or orientation was not possible.

It is an object of the invention to provide an improved transducer which at least minimises the disadvantages referred to above.

DISCLOSURE OF THE INVENTION According to one aspect the invention provides a transducer for measuring contact face pressure between a brush and commutator, the transducer including a transducer block made of a material having similar characteristics to the brush or of a dimensionally stable material, a transducer head, a recess in a face of the block for receiving the head and from which the head projects so that it may contact the commutator against which the block may be biased.

The transducer head may consist of any suitable transducer capable of providing an output the characteristics of which are representative of pressure to which the head is subjected. In one embodiment the head consists of a piezoelectric transducer and the electrical output obtained is representative of pressure.

The transducer head has a contact face which may abut the commutator. The contact face may be modified so as to more precisely contact the curved commutator surface. In one embodiment the contact face is provided with spaced feet. The feet are preferably parallel spaced strips having a width greater than the width of the mica undercut on the commutator or slots in the commutator.

The block may comprise a block of material made from the same substance as the brushes although this need not be the case. For example, where the brushes are made of carbon, the block is made of carbon. The block may be made of any other suitable material which is dimensionally stable. Other suitable materials which may be used are castable non-metallic materials.

The recess in the block is dimensioned so as to accurately and repeatably receive the transducer head and allow the head to project from the block for a short distance. In this way the head may contact a commutator or any other surface against which the block is biased. Since the head needs to be electrically coupled to detecting and display circuitry it is preferred that the recess leads into at least one passage for accommodating an electrical conductor or lead extending from the head. The passage may extend through the block or along an edge of the block. Preferably two such passages are present on opposed edges of the block. Such passage is placed so that the conductor does not foul or restrict movement of the brush-holder brush spring. In one embodiment the block is provided with a resilient pad on that face opposite the recess.

DISCLOSURE OF THE DRAWINGS The invention will now be described by way of example with reference to the drawings in which: Figure 1 is a perspective view of a known transducer head;

Figure 2 is a perspective view of a transducer head according to an embodiment of the invention;

Figure 3 is a perspective view of one end of a transducer block;

Figure 4 is a perspective view of a transducer block according to one embodiment;

Figure 5 is a perspective view of a transducer block according to another embodiment; Figure 6 is a perspective view of a transducer block with a transducer head fitted thereto; and

Figures 7 to 11 show various ways in which the transducer of the invention may be used to secure an indication of contact brush pressure. DETAILED DESCRIPTION OF THE DRAWINGS

Figure 1 shows the transducer head 14 of the Bintpres transducer previously referred to. The head 15 includes a piezoelectric device having a base 16, an end 17 which was normally contacted by the brush spring and electrical leads 18. The base 16 was biased against a brush within a brush holder. The configuration was such that repeatable results could not easily be obtained.

In Figure 2 a transducer head 20 modified in accordance with an embodiment of the invention is shown. A commutator 21 is shown diagrammatically. The base 22 of the head has feet 23 of a width wider than gaps G provided by Mica undercut portions on the commutator 21. Figure 3 shows an upper end of a transducer block 25 which forms part of a transducer of the invention. A resilient pad 26 provided on the end of the block 25. It is against this pad 26 that the brush spring may bear during use of the transducer. Passages 27 in opposite faces of the block 25 enable the electrical lead (not shown) from the transducer head to pass along the block 25 clear of brush spring arm contact area and the top of the brush. The dimensions of the passages 27 are chosen to suit the size of the lead and may typically be about 4 mm.

Figure 4 shows a transducer 30 block according to one embodiment of the invention. Block 30 is shorter than the block illustrated in Figure 5 and may be used to measure brush contact face pressure at worn brush length. The block 30 has a lead pas age 31 in opposed side faces and this passage continues along the contact face 32 and into recess 33. Recess 33 is dimensioned to receive the transducer head and to enable the head to project beyond face 32. A non-interference sliding fit is preferred between the head and the recess. Typically, the recess 33 has a depth of about 7 mm. A resilient pad 34 against which the brush spring may bear is shown.

Figure 5 shows a transducer block 37 of a length greater than block 30 in Figure 4. The Figure 5 block may be employed to measure brush contact face pressure at full brush length. Block 37 has a resilient pad 38, passage 39 for the electrical lead extending from the transducer head and a recess 40 for that head.

Figure 6 is a perspective view of a transducer 45 including a transducer block 46 and a transducer head 47. Lead 48 extends from the head 47 and along passage 49. The head 47 is proud of the face 50 by about 0.55mm. Figure 7 shows how the transducer of the invention may be used to determine brush contact pressure against commutator 52. The brush normally held by brush holder 53 is removed and replaced with either a long transducer block 54 which simulates a full length brush or a short transducer block 55 which simulates a worn brush. Clock spring 56 biases the block against the commutator 52. In this embodiment the upper end of the transducer block is convex. Transducer head 57 located within the recess in the block abuts the commutator. Figure 8 shows a similar arrangement to that illustrated in Figure 7 except that the upper end of the block is flat and the end of the spring is provided with a curved shoe 58.

Figure 9 shows an alternative to that illustrated in Figure 8. In this embodiment either block 54 or 55 is employed depending upon whether full or worn brush pressure is to be detected. A constant force springbell 59 biases the block and head 57 towards the commutator. Constant force springs 60 bias the block towards the commutator.

In Figure 10 either long or short block 62, 63 is located within holder 53 and receives head 57., The transducer is biased towards commutator 52 by spring 64.

In Figure 11 the arrangement shown is similar to that of Figure 9 except that a reaction/trailing brush holder 65 is used. The transducer head 57 is presented at right angles to the commutator 52 while the transducer blocks 66, 67 (long or short) are at the reaction angle.

The transducer of the invention is intended as a maintenance or production tool and is primarily used for static measurements. A brush is removed from its brush holder and replaced with the transducer of the invention. The transducer block simulates a brush and the head is accurately and repeatably held relative to the block so that it may be biased against the commutator.

The transducer of the invention may be used to provide a dynamic indication of brush pressure by using a shorter transducer block piggy backed onto an actual short brush.

The transducer of the invention may be used without removing the electrical machine or major sub- assembly items of the machine and may determine whether the brush holder spring cell needs adjusting or replacing. This enables the spring cells to be kept in the correct working range for the full brush to worn brush length conditions of operation as well as enabling sets of springs on a particular machine to be evenly matched during the course of normal duty and operation. The basis of determining if the spring cells require adjusting is the actual contact face pressure of the brush and not on whether the spring arm or coil tension appears to be correct on the top of the brush. The transducer of the invention which simulates an actual brush in a holder takes into account any side force friction and geometry.

Claims

CLAIMS:

I. A transducer for measuring contact force pressure between a brush and commutator, the transducer including a transducer block made of a material having similar characteristics to the brush or of a dimensionally stable material, a transducer head, a recess in a face of the block for receiving the head and from which the head projects so that it may contact the commutator against which the block may be biased. 2. The transducer of Claim 1 wherein the transducer head comprises a piezoelectric transducer having a contact face which may abut the commutator. 3. The transducer of Claim 2 wherein the contact face has spaced feet extending therefrom. 4. The transducer of Claim 3 wherein the feet comprise parallel strips of a width greater than the width of slots in the commutator.

5. The transducer of Claim 1 wherein the block is made of the same substance as that from which the brushes are made.

6. The transducer of Claim 1 wherein the block is made of carbon.

7. The transducer of Claim 1 wherein the recess has a depth greater than the thickness of the head so that the head may project a short distance from the block.

8. The transducer of Claim 1 including at least one passage extending from the recess and along the block for accommodating electrical conductors enabling the head to be electrically coupled to detecting and display circuitry.

9. The transducer of Claim 8 wherein two said passages are present and extending along opposed edges of the block. 10. The transducer of Claim 1 including a resilient pad on an end of the block remote from the recess.

II. The transducer of Claim 1 wherein the head projects beyond the block by about 0.55 mm. 12. The transducer of Claim 1 wherein an end of the block remote from the recess is convex in shape.

13. The transducer of Claim 1 wherein an end of the block remote from the recess is flat. 14. The transducer of Claim 1 wherein the transducer head is received at an inclined angle relative to the block such that the head may be presented at right angles to the commutator with the block being at an inclined angle relative to a radial axis through the commutator.