GB2051269A

GB2051269A - Preventing Brake Sticking in a Braked Electric Motor

Info

Publication number: GB2051269A
Application number: GB8016059A
Authority: GB
Original assignee: Moteurs Leroy Somer SA
Current assignee: Moteurs Leroy Somer SA
Priority date: 1979-05-17
Filing date: 1980-05-15
Publication date: 1981-01-14
Also published as: FR2456883B1; IT1143948B; DE3018832A1; FR2456883A1; GB2051269B; IT8048712A0; ES491563A0; DE3018832C2; ES8102432A1

Abstract

An electric instant-stop motor comprises an axially movable rotary disc 11 biased to be clamped between linings 27 by a non-rotary disc 18 when the same is not pulled on by an electromagnet 14. Upon energisation of the motor, the electromagnet 14 is energised and pulls on the disc 18 to release the brake. That surface 28 of the disc 18 which engages the armature 15 has an unevenness to prevent sticking of the disc on the armature upon de-energisation of the electromagnet. <IMAGE>

Description

SPECIFICATION Electric Motor The present invention related to a so-called "no-volts, instant-stop" motor, that is an electric motor having a brake which stops the motor immediately in response to cessation of energisation thereof.

Devices of this kind usually comprise at least two brake discs; one of them, hereinafter called the "moving disc", co-rotates with the motor shaft and the other, hereinafter called the "stationary disc", is solid, at least so far as angular movement is concerned, with the motor carcass. At least one of the discs can move axially and is biassed towards the other by a spring, a brake lining being provided between the two discs. An electomagnet which is in the energised state whenever the motor is in the energised state keeps the two discs apart from one another, so that there is no braking when the motor is energised. Upon cessation of energisation, the electromagnet becomes inoperative and allows the disc rigidly secured to the motor carcass to be moved by the spring into engagement with the other disc.

Occasionally, upon cessation of energisation of the electromagnet, the stationary disc may continue to stick to the electromagnet armature either because the two engaging surfaces mate up too closely or because residual magnetisation of the armature continues to keep the disc attracted to it due to the lack of an air gap.

It is an object of the present invention to provide a motor of the kind described hereinbefore which is free from any significant risk of sticking and which, therefore, operates reliably in all normal conditions.

According to the present invention there is provided a no-volts instant-stop motor which comprises a movable brake disc slidable on and co-rotatable with the motor shaft and a stationary slidable brake disc coaxial of the movable brake disc and solid, at least so far as angular movement is concerned, with the motor carcass and so biassed by spring means that one of the surfaces thereof engages with the movable disc by way of a friction lining, the other surface of the stationary disc being attractable by an electromagnet energisable simultaneously with energisation of the motor to engage the electromagnet armature, the armature-engaging surface of the stationary disc having a surface texture with unevennesses to prevent the latter disc from sticking completely to the armature.

Upon cessation of energisation of the electromagnet, the residual air gap left because of the unevenness is such that the immediate decrease in magnetic attraction is sufficient for the stationary disc to disengage from the electromagnet and co-operate with the moving disc.

For optimum results, the unevennesses of the stationary disc are of a height of substantially from 0.5 to 1 mm.

Advantageously, the second brake disc is produced by moulding of a ferromagnetic substance, the armature-engaging surface thereof being left untreated and having a surface texture of index N R2 Q3 referred to the LCA-CEA No 3 standard roughness tester. This embodiment couples cheapness of production with the technicai effect provided by the invention.

In an improved form of the invention, means are provided to compensate for possible warping of the brake disc left untreated after mould release; the point is that leaving disc surface untreated, although providing the required unevenness, may lead to the stationary disc being generally untrue and, therefore, ineffective, hence the need to compensate for buckling.

Advantageously, therefore, the electromagnet is secured to the motor carcass by way of adjustable peripheral abutment means.

For a better understanding of the present invention and to show how the same may be put into effect, reference will now be made, by way of example, to the accompanying drawing, in which: Figure 1 shows a partial longitudinal sectional view of a motor in accordance with the present invention, Figure 2 shows a view, on an enlarged scale, of a part of Figure 1, Figure 3 shows a sectional view on line Ill-Ill of Figure 1, and Figure 4 shows a sectional view on line IV--IV of Figure 3.

Referring to the drawings, the motor in accordance with the invention comprises a carcass 1 receiving a rotor 2 rigidly secured to a shaft 3.

A brake device 4 is rigidly secured to the carcass 1 by a number of peripheral screws 5 and is received in a casing embodied by a plate 6 receiving the screws 5 and by a plate 7 secured to plate 6 by four peripheral screws 8 (shown in Figures 3 and 4), the two plates 6 and 7 engaging with one another by way of a gasket 9.

In the casing, a movable disc 11 is fitted to the shaft 3 by way of a sleeve 12 which is secured to the shaft 3 and formed with longitudinal keyways 13, co-operating with corresponding keyways in the disc 11, so that the same is co-rotatable with the shaft 3 but is free to be displaced thereon.

The plate 7 receives an electromagnet 14 comprising an armature 1 5 and a winding 1 6 energised by way of a terminal strip 1 7. The winding 1 6 is energised simultaneously with the motor in known manner.

A stationary disc 18, coaxial of the shaft 3, carries a guide rod 19, sliding freely in a plug 21 screwed into an axial bore 22 in the armature 1 5 and locked by a backnut 23. A spring 24 bears on the plug 21 to urge the stationary disc 18 towards the moving disc 11.

As can be seen in Figure 3, the stationary disc 1 8 is formed with peripheral teeth 25 which engage in recesses 26 in the plate 6 to ensure that the disc 1 8 moves angularly with the plate 6 and the carcass 1 while remaining free to move axially.

Brake linings 27 are interposed between the facing surfaces of the disc 1 8, the disc 11 and the plate 6 and are carefully trued to serve as proper braking surfaces.

However, that surface 28 of the stationary disc 1 8 which is near the armature 1 5 has unevennesses (shown in Figure 2) of a height h of from 0.5 to 1 mm. In the example described, the disc 1 8 is a ferromagnetic moulding and the surface 28 thereof is left untreated at mould release, the moulding sand used being chosen to give the required height h of the unevennesses.

It has been found that the required unevenness or roughness is of the grade known as NR2Q3 measured by a standard roughness tester known as the LCA-CEA No. 3.

As a result of the surface 28 being left untreated, it may be untrue and, therefore, fail to engage satisfactorily with the armature 1 5. To obviate this disadvantage, the armature-carrying plate 7 bears on the plate 6 by way of four adjustable abutments in the form of screws 29 which are screwed into plate 6 and locked by nuts 31 (see Figures 3 and 4). The screws 29 can, therefore, be adjusted to tilt surface 32 of the armature 1 5 siightly so as to compensate for any distortion or warping in disc surface 28 and ensure that the surfaces 32 and 28 engage one another satisfactorily.

In operation, when the motor is energised and running, the winding 1 6 is also energised and the armature 15 pulls on the stationary disc 18, the same engaging satisfactorily with the armature 1 5 because of the adjustment provided by the screws 29.

When energisation of the motor ceases, energisation of the winding 1 6 ceases simultaneously. The disc 18 ceases to be pulled on and, because of the unevenness of the surface 28 and of the resulting residual air gap, the disc 18 does not stick to the armature 1 5 and is, therefore, immediately urged by the spring 24 to compress the linings 27 between the stationary disc 18, the moving disc 11 and the plate 6. The disc 11 is, therefore, heavily braked and the motor stops immediately.

The invention, therefore, obviates any risk of the disc 1 8 sticking accidentally so that the brake fails to operate. The invention provides the further advantage that very low-cost production is possible.

Claims

1. A no-volts instant-stop motor which comprises a movable brake disc slidable on and co-rotatable with the motor shaft and a stationary slidable brake disc coaxial of the movable brake disc and solid, at least so far as angular movement is concerned, with the motor carcass and so biassed by spring means that one of the surfaces thereof engages with the movable disc by way of friction lining, the other surface of the stationary disc being attractable by an electromagnet energisable simultaneously with energisation of the motor to engage the electromagnet armature, the armature-engaging surface of the stationary disc having a surface texture with unevennesses to prevent the latter disc from sticking completely to the armature.

2. A motor according to Claim 1, wherein the unevenness of the stationary disc are of a height of substantially from 0.5 to 1 mm.

3. A motor according to Claim 1 or 2, wherein the second brake disc is produced by moulding of a ferromagnetic substance, the armatureengaging surface thereof being left untreated after mould release and having a surface texture of index NR2Q3 referred to the LCA-CEA No. 3 standard roughness tester.

4. A motor according to Claim 3, wherein means are provided to compensate for possible warping of the brake disc left untreated after mould release.

5. A motor according to any one of the preceding claims, wherein the electromagnet is secured to the motor carcass by way of adjustable peripheral abutment means.

6. A no-volts instant-stop motor, substantially as hereinbefore described with reference to, and as shown in, the accompanying drawing.

7. Any novel feature or combination of features described herein.