The present invention relates to a combination pneumatic chuck having a position detecting mechanism for detecting a chuck position of a workpiece by jaw members.
There is a known combination pneumatic chuck having a chuck function of chucking a workpiece and a stroke function of moving the chucked workpiece forward and rearward as disclosed in Japanese Patent Application Laid-open No. 8-19983, for example. In this pneumatic chuck, a stroke air cylinder mechanism formed of a larger-diameter piston and a larger-diameter rod and a chuck air cylinder mechanism formed of a smaller-diameter piston and a smaller-diameter rod are coaxially incorporated in a double layers in inner and outer positions in a casing, a chuck head is mounted to the rod of the stroke air cylinder mechanism, a plurality of jaw members for grasping the workpiece are mounted to the chuck head such that the jaw members can be opened and closed, and the jaw members are opened and closed by the rod of the chuck air cylinder mechanism.
To such a pneumatic chuck, in general, a position detecting mechanism formed of a magnet and a magnetometric sensor is attached so as to detect chucking or releasing of the workpiece by the jaw members and to produce control signals for automatic operation. Specifically, magnets are mounted to the jaw members and a sensor is mounted to the casing to directly detect operating positions of the jaw members. Otherwise, a magnet is mounted to the piston of the chuck air cylinder mechanism to detect an operating position of the piston, thereby indirectly detecting opening and closing positions of the jaw members.
However, because the chuck head for retaining the jaw members is driven by the stroke air cylinder mechanism in the above prior-art combination pneumatic chuck, it is difficult to directly detect the operating positions of the jaw members by mounting the sensor to the chuck head that is displaced. Because the piston and the rod of the chuck air cylinder mechanism are incorporated into the piston and the rod of the stroke air cylinder mechanism such that the stroke air cylinder mechanism exists between the chuck air cylinder mechanism and the casing, it is also difficult to detect the position of the piston of the chuck air cylinder mechanism.
It is a technical object of the present invention to provide a combination pneumatic chuck with a chuck air cylinder mechanism and a stroke air cylinder mechanism coaxially incorporated in inner and outer positions in the casing, wherein chuck operation of a workpiece by jaw members can be detected reliably by a simple structure.
To achieve the above object, a combination pneumatic chuck according to the invention comprises: a casing having therein a cylinder bore; a stroke first air cylinder mechanism including a larger-diameter first piston housed for sliding in the cylinder bore in the casing and a larger-diameter first rod having a base end portion connected to the first piston and a tip end portion extending from of the casing; a chuck second air cylinder mechanism including a smaller-diameter second piston housed for sliding coaxially in the first piston and a smaller-diameter second rod having a tip end portion connected to the second piston and extending to an inside of the first rod and a base end portion extending to such a position as to project from the first piston and to face a position detecting portion of the casing; a chuck head mounted to the tip end of the first rod for moving forward and rearward in response to expansion and contraction of the first rod; a plurality of jaw members for grasping a workpiece and mounted for opening and closing to the chuck head; a converting mechanism disposed between the jaw members and the second rod in the chuck head for converting expanding and contracting operations of the second rod into opening and closing operations of the jaw members; and chuck position detecting means which is for detecting opening and closing positions of the jaw members and which includes a detected member mounted to the base end portion of the second rod and a position sensor mounted to a position detecting portion of the casing for detecting the detected member.
According to the combination pneumatic chuck of the invention having the above structure, by a simple structure in which: the base end portion of the second rod of the second air cylinder mechanism projects from the first piston of the second air cylinder mechanism and extends to such a position as to face the position detecting portion of the casing; the detected member is mounted to the base end portion; and the position sensor is mounted to the position detecting portion of the casing, the opening and closing positions of the jaw members can be indirectly detected by detecting the operating position of the rod of the first air cylinder mechanism even in the structure in which the first air cylinder mechanism is incorporated into the second air cylinder mechanism without extensively modifying the structure.
According to a concrete embodiment of the invention, the position detecting portion is in a small cylindrical shape of such a size that the base end portion of the second rod is fitted into the position detecting portion and is formed to project outward along an axis at a central portion of the base end face of the casing, at least one sensor mounting groove is formed in an outer face of the position detecting portion, and the position sensor is mounted in the sensor mounting groove.
According to another concrete embodiment of the invention, the pneumatic chuck includes stroke position detecting means which is for detecting a stroke position of the chuck head and which has a detected member mounted to the first piston and a position sensor mounted to the casing for detecting the detected member.
According to a preferred embodiment of the invention, the pneumatic chuck includes a pair of stroke ports for supplying compressed air to pressure chambers on opposite sides of the first piston and a pair of chuck ports for supplying compressed air to pressure chambers on opposite sides of the second piston and the ports are concentrated on the base end face of the casing.