| 摘要 |
A suction chamber is provided in the rear portion of a pad body remote from an external pad supporting surface. The fore end portion of the pad body facing the pad supporting surface is divided into a plurality of sucking compartments for communication with the suction chamber. An air flow passage is provided for communication with the suction chamber. Valve mechanisms are provided in air flow paths between the respective sucking compartments and the suction chamber and are closable by a sucked air flow occurring during vacuum suction. Further, an automatic switching valve is provided in a part of the air flow passage in such a manner that the switching valve is caused to open in response to abutment against the pad supporting surface of the pad body. The air flow passage is formed in such a manner that a direction of force acting to cause the automatic switching valve to open differs from a direction of counteractive force against a spring structure that normally urges the switching valve to close. |
