Tools – Wrench – screwdriver – or driver therefor – Responsive to torque on work
Reexamination Certificate
1999-06-24
2001-03-27
Smith, James G. (Department: 3723)
Tools
Wrench, screwdriver, or driver therefor
Responsive to torque on work
C081S057130, C173S010000, C227S008000
Reexamination Certificate
active
06205894
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an automatic stop device for use in a screw striking machine and, in particular, to an automatic stop device for use in a screw striking machine which automatically stops an air motor when a screwing operation is completed.
In addition, the present invention relates to an automatic stop device which can automatically stop the operation of the air motor when the screwing depth of the screw reaches a given depth especially in a condition that a screw is struck onto a member to be screwed in a floating condition by a screw striking machine and the screw is then rotated and tightened.
2. Description of the Related Prior Art
Conventionally, a screw striking machine uses high pressurized air as a power source. A driver bit connected to a piston of an air cylinder is driven and rotated by an air motor to thereby strike a screw into a member to be screwed. In this type of screw striking machine, as a safety device, a contact arm is disposed and projected from the nose portion of the screw striking machine. The contact arm is energized by a spring in a direction where the screw is struck. Due to the contact arm, a trigger lever is operable when the leading end portion of the contact arm is pressed against the surface of the member to be screwed and the other end portion of the contact arm is butted against a contact arm stopper disposed within the screw striking machine.
If the trigger lever is actuated, then a piston within the air cylinder is rapidly lowered; and, in response to this, the driver bit connected to the piston drives a screw into the member to be screwed such as a building material or the like to a certain degree and, at the same time, the locking of the contact arm by the contact arm stopper is removed, so that the air motor drives and rotates the driver bit to thereby screw the screw into the member to be screwed. If the operation of the trigger lever is removed, then the operation of the air motor is caused to stop, and thus the piston and driver bit respectively move upward to return back to their wait positions.
As for another kind of a screw striking machine, when a screwing operation is completed, the operation of an air motor is automatically stopped to thereby control the screwing depth of a screw to a constant depth. In an automatic stop device for use in the screw striking machine of this type, the device includes an open/close valve in an air supply pipe passage to an air motor, and switches the open/close valve by a contact arm to thereby stop the operation of the air motor automatically.
In particular, if the screw is rotationally driven by the air motor and is thereby screwed into the member to be screwed, then a distance between the screw striking machine and the member to be screwed decreases, and the contact arm is further pushed in toward the main body side of the screw striking machine. In the above-mentioned automatic stop device, at the time of completion of the screwing operation, the contact arm presses against the stem of the open/close valve to thereby switch the open/close valve over to its pressurized air cut-off position, thereby stopping the operation of the air motor.
In another type of automatic stop device, a device is also structured such that, if a piston connected to a driver bit reaches its bottom dead point or one end of its travel as a screw is screwed, then a seal member attached to the piston cuts off an air supply passage to an air motor to thereby stop the operation of the air motor.
When striking a screw into a member to be screwed with the screw striking machine, in order for the driver bit to be able to drive and rotate the screw positively, it is necessary to press the contact arm of the screw striking machine against the member to be screwed with a certain degree of pressure. However, if the pressing load is excessive, then the driver bit and piston are pushed in toward the main body side of the screw striking machine prior to completion of the screwing operation, with the result that the contact arm is also pushed in. In particular, in a screw striking machine of a type that an open/close valve can be switched by the contact arm, if the above-mentioned state occurs, then there arises a problem that the operation of the air motor is caused to stop prior to completion of the screwing operation.
On the other hand, if the load with which the screw striking machine is pressed against the member to be screwed is too small, then there is a possibility that the screw striking machine can be removed from the surf ace of the member to be screwed due to a reactive force produced when the screw is struck by the screw striking machine. In a screw striking machine of a type that, when a piston reaches its bottom dead point, an air supply passage to an air motor is cut off, if the above-mentioned state occurs, then the piston reaches the bottom dead point prior to completion of the screwing operation, thereby causing the operation of the air motor to stop.
SUMMARY OF THE INVENTION
As described above, in the conventional screw striking machine including an automatic stop device, there is found a problem that the screw is tightened poorly if the pressing load of the screw striking machine against the member to be screwed is excessive or too small. The invention aims at eliminating the drawbacks found in the above-mentioned conventional automatic stop device for use in a screw striking machine. Accordingly, it is a first object of the invention to provide an automatic stop device for use in a screw striking machine which, regardless of the pressing load to be applied to the screw striking machine, can continue the rotation of an air motor positively until a screwing operation is completed, thereby being able not only to prevent the poorly screwed screw but also to facilitate the screwing operation.
In addition, it is a second object of the invention to provide an automatic stop device for a screw striking machine which, even if the screw striking machine, in its screwing operation, is strongly pressed against a member to be screwed and a piston is thereby pushed into the main body of the screw striking machine, can prevent effectively an air motor from being stopped and can stop the air motor for the first time on completion of a given screwing operation. Moreover, the present invention also aims to attain the above-mentioned operation even in the short duration of an actual screwing operation, for example, within 0.1 second.
In attaining the above-mentioned first object, according to the invention, there is provided an automatic stop machine for a screw striking machine includes a driver bit, an air pressure cylinder having a piston, and an air motor driving the piston and rotationally driving the driver bit. The automatic stop machine comprises a primary open/close valve, a contact arm, and an air passage. The primary open/close valve is disposed in an air supply passage to the air motor. The contact arm freely slidable along a nose portion of the screw striking machine, projects from the leading end of the nose portion, and stops the air motor by closing the primary open/close valve when the contact arm is pushed into a main body of the screw striking machine and is moved upwardly as the screw is screwed. The air passage in which pressurized air passes from a space defined by a back surface of the piston in the piston when the piston reaches the vicinity of bottom dead point. Pressure of the pressurized air supplied through the air passage and upward movement of the contact arm cooperatively cause the primary open/close valve to close when the piston reaches the vicinity of bottom dead point.
Preferably, the automatic stop machine for a screw striking machine further comprises a gear including a center hole with a spline groove in the screw striking machine, wherein the driver bit includes a spline shaft to be inserted into the gear and is rotatably driven by the air motor through the gear.
It is more preferable that the pressure of the pressurized ai
Max Co. Ltd.
Morgan & Lewis & Bockius, LLP
Shakeri Hadi
Smith James G.
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