GB2189326A

GB2189326A - Torque overload control system

Info

Publication number: GB2189326A
Application number: GB08609544A
Authority: GB
Inventors: Raymond Rennison
Original assignee: Coal Industry Patents Ltd
Current assignee: Coal Industry Patents Ltd
Priority date: 1986-04-18
Filing date: 1986-04-18
Publication date: 1987-10-21
Also published as: DE8705539U1; GB2189326B; DE3712575A1; GB8609544D0

Description

GB 2 189 326 A SPECIFICATION Bywayof example only, oneform of control

system according tothe invention isdescribed Control systems below with reference to the accompanying drawings in which:

This invention concerns a control system. 70 Figure 1 is a diagrammatic arrangement of the In particular, but not exclusively, the present system; and invention has referenceto a control systernfor Figure2 is a perspective view of the coupling.

controlling the rotation of a shaft in accordancewith Referring to the drawings, a control system thetorque. indicated by the numeral 1 consists of a dog tooth When a shaft is employed to drive a loadJor 75 coupling 2 the drive member4 of which is connected example the conveying screw fortransporting to shaft 3 of an electric motor 6. The driven member 8 particulate material, the torque varies dependent of the coupling is connected to a conveying screw 10 upon the magnitude of that load and it is important of a screw conveyor employed for example to feed to ensure that a predetermined limit is not exceeded. particulate coal into a stoker, particularly an Various types of overload protection devices are 80 underfeed stoker. The drive and driven members 4,8 known and have been used with effect overthe of coupling 2 have interspersed in abutting years. Perhaps one of the simplest involves using relationship between their respective teeth 12,14 shear pins which fail upon attainment of the blocks 16 of rubber or other elastomeric material predetermined torque limit. The disadvantage of which carry a contact ring 18.

employing such an arrangement is the work 85 A microscitch 20 is disposed in close adjacencyto necessarily involved in replacing the shear pins as the ring 18 which is capable of contacting the this is time consuming and can prove difficult. actuating arm 22 of the microscitch. The microswitch Furthermore, there is no automatic cut-off forthe 20 is connected to a logic control unit 24 which is in drive motor. turn arranged forthe control of the electric motor6.

An object of the present invention isto provide a 90 In operation,the conveying screw 10 is driven by simple and yet effective control system. motor6through the shaft3 and coupling 2. If there Accordingly, the invention provides a control should be a blockage of the screw 10, caused for system including a coupling fora rotatable shaft,the example bytramp material, thetorque will increase coupling having a drive member and a driven and in so doing the blocks 16 of elastomeric material member, an elastomeric element interposed 95 will distortthis causing the contact ring 18 to move between the drive and driven members, and a trip axially. The ring 18 in its actuating position, shown in mechanism associated with the element and ghosted outline at 1Win Figure 1, operates the actuable thereby upon attainment of a microswitch 20 which through the!control unit 24 predetermined torque in th shaft. stops the motor 6 and thereafter reverses polarity The elastomeric element may be of any material 100 such thatthe motor 6 can be driven in the opposite deformable in a plane perpendicularto an applied direction to tryto freethe blockage. The reverse force. For example,the material may be rubber or a running of motor 6 is initiated bythe control unit and spring steel ring or any eq u iva lent thereof. continuesfor a preset time, therafter normal rotation The coupling may conveniently be in theform of a is restored. If the cause of the blockage is not dog drive and the elastomeric element may 105 removed bythe reverse rotation and thetorque comprise a number of blocks disposed in abutting increase again occasions the microswitch to trip out, relationship with the teeth of the drive and driven the unitwill repeat the reverse running twice more members. before finally cutting off powerto the motor 6.

A contact ring may be attached to the freefaces of Thereafterthe blockage must be removed manually.

the elastomeric element blocks or held againstthe 110 The control system of the present invention thus faces by a spring. provides a simple arrind yet effective means of The trip mechanism may be a microswitch protection against overload by utilising the connected to a logic control unitwhich is in turn used distortion characteristics of elastomeric material.

to control a drive motorwith the rotatable shaft The control system can also be employed for carrying the drive member of the coupling. 115 measuring torque of a rotating shaft, and this The logic control unit is designed in such a way application can be achieved by monitoring the that after receiving a trip signal from the microswitch displacement of the elastomeric element. Since this to switch off the drive motor, indicating the is related to the applied torque.

attainment of a predetermined torque on the shaft,

Claims

the unit then switches the drive motor into reverse 120 CLAIMS for a

preset time, thus affording the opportunityfor the cause of the high torque to be removed. The unit 1. A control system including a coupling fora then automatically switches the motor backto its rotatable shaft, the coupling having a drive member original direction. If the cause of the high torque is and a driven member, an elastomeric element not removed by reverse running afterthe first 125 interposed between the drive and driven members, attempt, the unit will allowtwo further attempts to be and a trip mechanism associated with the element made automatically by reverse running. If failure and actuablethereby upon attainment of a again results, powerto the motor is cut off until the predetermined torque in the shaft.

cause is removed manually. Once removal has been
2. A system according to claim 1 in which the effected, the control unit is reset. 130 coupling is in the form of a dog drive andthe 2 GB 2 189 326 A 2 elastomeric element comprises a numberof blocks in abutting relationship between respective teeth of the drive and driven members.
3. A system according to claim 2 in which a contact ring is attached to the free faces of the blocks of the elastomeric element.
4. A system according to anyone of the preceding claims in which the trip mechanism is a microswitch.
5. A system according to claim 4 in which the microswitch is connected to a logic control unit adapted to control a drive motorforthe rotatable shaft.
6. A control system substantially as hereinbefore described with reference to Figures land 2 of the accompanying drawings.

Printed for Her Majesty's Stationery Office by Croydon Printing Company (UK) Ltd,8187, D8991685. Published by The Patent Office, 25 Southampton Buildings, London, WC2A 'I AY, from which copies maybe obtained.