| 摘要 |
A fluid-operated ram, for example comprising a cylinder 10 and piston 12, is provided for actuating a device such as a chuck having jaws 15. When the jaws are moved by the ram to grip a workpiece this constitutes a limiting position which impedes the flow of fluid thus causing a build-up of fluid pressure within the ram. This build-up can be detected to give an indication as to when a workpiece has been securely and safely gripped. To ensure that a false indication is not given if the ram reaches an end of its working stroke before the workpiece is securely gripped, means (22) are provided to relieve pressure within the ram when the ram reaches an end of its working stroke. |
