GB1226978A - - Google Patents

Abstract

1,226,978. Screwing-up and unscrewing nuts, &c. DESOUTTER BROS. Ltd. 12 Sept., 1969 [29 Nov., 1968], No. 56653/68. Addition to 1,180,771. Heading B3N. In a power-operated impact wrench or screwdriver having in accordance with the main patent an inertia cylinder 141 coupled to rotary hammers 150 by resilient means which constrain the inertia cylinder from moving relative to the hammers until the impact delivered to an anvil 151 reaches a predetermined value whereupon the inertia cylinder moves in relation to the hammers and acts to increase the amount of cyclic disengagement of the hammer from the anvil thereby operating control means for interrupting the supply of power to the tool, the resilient means is in the form of a pair of spring levers 149 each of which is integral with a hammer 150 and supported in a bore 148 in the inertia cylinder 141. A spring 143 and balls 140 which are disposed in inclined grooves 139 in a drive spindle 137 reciprocate the inertia cylinder 141 to engage and disengage the hammers 150 and anvil 151 as the spindle and the inertia cylinder are driven by a vane type air motor 125 through planetary gearing 138. The spring levers 149 project from the bores 148 into eccentric counter bores 152 which accommodate flexing of the levers. A waisted portion 153 of each spring lever 149 provides a different bonding resistance in different radial directions so that the levers 149 may be rotated about their longitudinal axes to adjust the maximum torque delivered by the tool. For this purpose each spring lever 149 has splines 154 which are disengageable from splines in the bore 148 by turning a cover plate 155 to expose a hole 156 and then inserting a tool to depress the lever against the action of a spring 157. Each spring lever 149 can thus be turned and then released to occupy a new position. In operation, the spring levers 149 remain in contact with one side of the counter bores 152 so that the inertia cylinder 141 and the hammers 150 move in unison until the resistance to movement of the anvil 151 under the impact of the hammers reaches the predetermined value whereupon the cylinder 141 continues to move when the hammers strike the anvil and the levers 149 are flexed. Subsequent rebound of the inertia cylinder 141 increases the disengaging movement of the hammers from the anvil so that the cylinder 141 strikes a trigger 134 which unseats a ballvalve 130 to allow closure of a spring-loaded piston valve 120 for cutting off the air supply to the motor 125. The piston valve 120 remains in the closed position until the air supply is terminated by release of a push-button valve 110 which is initially depressed to cause clockwise rotation of the motor. A second push-button valve 111 provides for anti-clockwise rotation but as described the torque control operates only during clockwise rotation. In other embodiments the maximum torque delivered by the tool is adjusted not be varying the stiffness of the spring levers but by variably pre-stressing them.