Pneumatic screw punching machine

Abstract: A pneumatic screw punching machine includes a poppet portion (44) on a piston (28) of an air cylinder (23) and a piston catcher (43) disposed inside a head cap (24). The piston is held when the poppet portion fits into the piston catcher in a standby state. A retaining ring (40) in the head cap supports a head valve (39). A circumferential groove (41) is formed in an inner peripheral surface of the front part of the head cap and a ring-like seal (42) is fitted into the groove. When a driver bit (29) is to be changed, fitting bolts are removed and a housing (22) and the head cap are separated from each other. Then, the head cap, the head valve, the seal, the piston and the driver bit can all be removed together from the housing.

Description: This invention relates to a pneumatic screw punching machine. In the field of pneumatic tools, a pneumatic screw punching machine is known by means of which a screw is punched to a certain extent into a workpiece by a driver bit coupled to a piston and is then fastened by driving and rotating the driver bit by an air motor (See for example EP-A-0 727 284). Fig. 5 of the accompanying drawings shows a cylinder head portion of such a known pneumatic screw punching machine. In this drawing, reference numeral 1 denotes a housing and a driver bit 4 is shown coupled to a piston 3 of an air cylinder 2 inside this housing 1. A head cap 5 is coupled by a bolt (not shown) to an open end portion of the housing 1 and a seal 6 is interposed between the housing 1 and the head cap 5 to prevent leakage of air from an air chamber 7 inside the housing 1. A head valve 8 fitted into the head cap 5 is brought into pressure contact with a valve seat 9 on the open end of the air cylinder 2 by pilot pressure acting on the rear surface (right side in the drawing) in the standby state and cuts off an air passage between the air chamber 7 and the air cylinder 2. When a stem 12 of a trigger valve 11 is pushed by operating a trigger lever 10 pivotally mounted to the housing 1, the pilot pressure acting on the rear surface of the head valve 8 is discharged and the head valve 8 is moved back by the pressure in the air chamber 7. In consequence, pressure from the air chamber 7 is supplied into the air cylinder 2, and the piston 3 and the driver bit 4 advance, eject a screw inside a nose (not shown) and punch it into a workpiece. Subsequently, the air motor (not shown) drives and rotates the driver bit 4 to thereby fasten the screw to the workpiece. When any component inside the housing 1 is exchanged or is repaired, the cap fitting bolt is removed to separate the housing 1 and the head cap 5. When the distal end portion of the driver bit 4 is worn out and must be exchanged for a new one, for example, the valve seat 9 at the head of the air cylinder 2 is removed or the air cylinder 2 is withdrawn as a whole from the housing 1 to take out the piston 3 and the driver bit 4, and the driver bit 4 is then exchanged. Thus, this pneumatic screw punching machine involves the problem that the procedures for disassembly and reassembly are complicated and time-consuming. Other problems are that the head cap 5, the seal 6, the head valve 8 and the valve seat 9 are likely to be reassembled in the wrong way, or a part is likely to be lost, or the seal, etc, may be caused to be deformed during the maintenance operation. According to the present invention there is provided a pneumatic screw punching machine in which an air cylinder is accommodated in a housing, a head cap is fitted to an opening of said housing at the cylinder head end by way of a ring type seal, and a slidable head valve is fitted into said head cap to control operation of said air cylinder; characterized in that a poppet portion is formed on a piston of said air cylinder, a piston catcher is disposed inside said head cap so that said poppet portion of said piston and said piston catcher can engage and disengage relative to each other; a retaining ring for said head valve is fitted to said head cap; and an engagement portion for holding said seal is associated with said head cap; whereby when said head cap is separated from said housing, said head valve, said seal, said piston and a driver bit connected to said piston can all be removed together with said head cap from said housing. An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, in which:- Fig. 1 is a sectional side view of a pneumatic screw punching machine according to the present invention; Fig. 2 is a sectional view of a cylinder head portion of the machine shown in Fig. 1; Fig. 3 is a sectional view of a housing and a cylinder cap of the machine, in a separated state; Fig. 4 is a sectional view of the apparatus of Fig. 3 when a piston is removed; Fig. 5 is a sectional view showing a cylinder head portion of a pneumatic screw punching machine according to the prior art. Fig. 1 shows a pneumatic screw punching machine 21. An air cylinder 23 is fitted into a housing 22 and a head cap 24 is coupled to an open end of the housing 22 at the cylinder head end by means of bolts (not shown). A loop-shaped handle 25 is formed integrally with the head cap 24 and pressurised air is supplied to an air chamber 27 inside the loop-shaped handle 25 by connecting an air hose to a connector 26 disposed at the lower end of the handle 25. An air motor 30 for driving and rotating a driver bit 29 coupled with a piston 28 inside the air cylinder 23 is juxtaposed with the air cylinder 23. Power from the air motor 30 is transmitted to a drive gear 33 through a reduction gear mechanism 32 disposed between the distal end of the air cylinder 23 and a nose portion 31. The drive gear 33 and the driver bit 29 are coupled by a spline coupling, whereby the piston 28 and the driver bit 29 are slidable in the axial direction. A screw feed device 34 disposed on the side surface of the nose portion 31 comprises an air cylinder and a ratchet type feed pawl in the manner of known pneumatic nail punching machines, whereby screws stored in a screw magazine 35 can be serially supplied into the nose portion 31. Referring still to Fig. 1, a contact arm (not shown) capable of sliding in a screwing direction is disposed on the rear surface of the nose portion 31 and a screw guide 36 fitted to the distal end of the contact arm protrudes from the nose portion 31 in the screw ejecting direction. A chuck capable of being opened and closed is pivotally fitted to the distal end of the screw guide 36, and is closed by a spring 38 in a standby state. As shown in Fig. 2 on a larger scale, a cup-shaped head valve 39 is fitted into the head cap 24 and a retaining ring 40 is fitted to the front part (left side in the drawing) of the head valve to hold it in position. A circumferential groove 41 is formed in the inner peripheral surface of the front portion of the handle 25 (integral with the head cap 24) and a ring-like seal 42 is fitted into this groove 41. A piston catcher 43 made of flexible rubber is disposed at the center of the inner wall surface of the head cap 24 and protrudes forward through a central hole in the head valve 39, and a poppet portion 44 of the piston 28 is inertable in, and removable from, a central hole in the piston catcher 43. In the standby state shown in Fig. 1, pilot pressure is supplied to the outer peripheral surface (on the right in the drawing) of the rear part of the head valve 39 through a trigger valve 45 inside the loop-shaped handle 25, whereby the head valve 39 comes into pressure contact with a valve seat 46 fitted on the outside of the air cylinder 23, and cuts off an air passage between the air chamber 27 and the air cylinder 23. In operation, the screw guide 36 is engaged with a workpiece surface and the trigger lever 47 disposed on the loop-shaped handle 25 is operated. Thereby the trigger valve 45 is switched to the open position, the pilot pressure acting on the head valve 39 is released, and the head valve 39 is moved by the pressure of the air chamber acting on the front outer peripheral surface of the head valve, so that it separates from the valve seat 46. Consequently pressurised air flows from the air chamber 27 into the air cylinder 23 to activate the piston 28, whereby the poppet portion 44 leaves the piston catcher 43 and advances inside the air cylinder, and the driver bit 29 ejects the screw located in the nose portion 31. Subsequently, the feed pressure to the air motor 30 rises to activate the air motor 30, whereby the driver bit 29 is driven and rotated, to screw the screw into the workpiece. When the screw has thus been fastened and the air motor 30 comes to halt, the piston 28 and the driver bit 29 are returned to their standby positions by the pressure of a blowback chamber 48 defined between the outer peripheral surface of the front part of the air cylinder 23 and the housing 22, and the poppet portion 44 of the piston 28 is once again received in the piston catcher 43 and stops there. When the driver bit 29 needs to be changed due to wear of its distal end, or breakage, the bolts that couple the housing 22 and the head cap 24 are first removed so as to separate these parts from each other, as shown in Fig. 3. Following that, the head cap 24, the head valve 39, the seal 42, the piston 28 and the driver bit 29 can all be removed together from the housing 22. As the driver bit 29 is pulled out, the poppet portion 44 of the piston 28 is readily released from the piston catcher 43, as shown in Fig. 4, and the driver bit 29 can then easily be exchanged. After the driver bit 29 has been changed, the poppet portion 44 of the piston 28 is pushed back into the piston catcher 43 of the head cap 24, the head cap 24 is fitted to the housing 22 and the fitting bolts are fastened, i.e. by a procedure opposite to that of the disassembly process, and the operation of changing the driver bit is thus completed. It will thus be understood that the head valve, the seal, the piston and the driver bit can be removed together with the head cap when the head cap is removed from the housing, and disassembly can thus be carried out easily. Further, the possible loss of these components and mistake in re-assembly can be eliminated, and maintenance procedures can be substantially improved.

Claims: A pneumatic screw punching machine in which an air cylinder (23) is accommodated in a housing (22), a head cap (24) is fitted to an opening of said housing at the cylinder head end by way of a ring type seal (42), and a slidable head valve (39) is fitted into said head cap to control operation of said air cylinder; characterized in that a poppet portion (44) is formed on a piston (28) of said air cylinder, a piston catcher (43) is disposed inside said head cap so that said poppet portion of said piston and said piston catcher can engage and disengage relative to each other; a retaining ring (40) for said head valve is fitted to said head cap; and an engagement portion (41) for holding said seal is associated with said head cap; whereby when said head cap is separated from said housing, said head valve, said seal, said piston and a driver bit connected to said piston can all be removed together with said head cap from said housing.

Inventors: TANAKA HIROSHI, TANAKA, HIROSHI
Applicants: MAX CO LTD, MAX CO., LTD.
Application year: 1998
Main classification: B25B21
IPC codes: B25B21