| 摘要 |
A method of controlling a pneumatically operated servo-motor (1) having a linearly movable operating rod (6) is described in which the actual position of the operating rod is monitored continuously during each stroke, and when the rod reaches a position which lies a predetermined amount in front of a limit position reached during the preceding stroke the speed at which the operating rod travels towards the corresponding limit position of the current stroke is modified. In particular the method is used in a clutch actuating servo-motor to brake the speed of the operating rod at a position which corresponds to the initial contact between the clutch friction surfaces when the rod is moving to engage the clutch, so that the free travel of the clutch is taken up as quickly as possible, but the actual engagement is slowed in order to avoid undesirable jerkiness and wear. For this purpose a servo-motor (1) is provided with an electrical pick-up (18) which is mounted on an extension member (20a) of the operating rod (6) so that the pick-up (18) follows faithfully the linear motion of the operating rod. The pick-up (18) is in sliding contact with a ribbon potentiometer (16) by which an electrical signal corresponding to the actual position of the operating rod at any time may be obtained. An electrical signal corresponding to the limit position of the operating rod (6) for use in controlling the next stroke is also derived, either from the pick-up (18) or alternatively from a separate pick-up (19) co-operating with a further ribbon potentiometer (17), the pick-up (19) being arranged to move only in response to a change in the limit position from one stroke to the next.
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