Patent GB-1261184-A (GB)
Title: Improvements in or relating to cranes
Inventor: HOWLETT FRANCIS CHARLES
IPC: B66C13/18
Filed: 1968-04-29
Abstract: 1,261,184. Control of motors. CLARKE CHAPMAN-JOHN THOMPSON Ltd. 25 April, 1969 [29 April, 1968], No. 20236/68. Heading H2J. In a crane adapted for automatic programme control, the slewing motion is altered by resetting the two end positions in turn, the anticlockwise limit being reset by moving the crane to the desired position using manual control. Cam-shaft 10 is isolated from the crane drive by disengaging clutch 8, and a setting clutch 18 is engaged. A setting motor S.M. then turns shaft 10 through shaft 19, gearing 20, shaft 21, and clutch 18. The setting motor is stopped when cam 5 operates limit switch 16, the respective clutches 18, 8, being then disengaged and re-engaged. Shaft 10 has now been repositioned relative to shaft 2 so that the slewing motion is stopped under automatic control when limit switch 12 is operated by cam 4. The limit of the clockwise slewing motion is reset similarly by first disengaging clutch 9 and engaging clutch 22. The setting motor and the several clutches are controlled by relays associated with push-button switches, a pilot lamp indicating that the resetting operation is complete, Fig. 3 (not shown). An automatic control switch controls contactors to cause the slewing drive motor to operate the motion in the lefthand or right-hand directions, Fig. 4 (not shown). An additional cam on each shaft 10, 11, reduces the speed of the slewing motor before it is stopped. Alternatively, a second limit switch for each cam 5, 7, may be used for this purpose. The setting and control cams for luffing motion are similar to those described, alternative pairs of limit switches for luffing-in and luffing-out being provided. The same setting motor and pilot lights can be used for both slewing and luffing, Figs. 7, 8 (not shown). When a control switch 56 is moved to the left, relays U, A are energized to prepare two grab barrels to turn in the twisting direction, relays CR, CG, being energized whereby the holding barrel is held stationary whilst the other barrel rotates to close the grab. Limit switch 35 then opens to de-energize the relay CG, both barrels rotating to hoist the grab. When the grab reaches a height to close switches 37, 39, the slewing and luffing contactors L, IN, are energized and relay M responds to stop hoisting. Limit switches 40, 12, then open to slow down and stop leftward slewing, limit switches 42, 45 opening to slow down and stop the luffing-in motion. Limit switches 17, 28 are operated to energize relay D and lower the closed grab until switch 33 causes the grab to open. When control switch 56 is moved to the right, the grab is hoisted until switches 37, 39, are closed, means being provided to prevent opening of the loaded grab during transverse movement. During slewing and luffing to the loading location, the grab is kept fully open. When the grab arrives over the loading position, limit switches 27, 16, stop the luffing and slewing motions, and the grab is lowered until a slack rope prevention control becomes operative. Sudden changes of speed of the luffing and slewing motors are prevented by means responsive to armature voltage so that the final speed step is not operative until the motor has reached a suitable speed on a preceding step. Contacts operable from the relays A, U, bridge the speed step lines. In a modification, the cam-shaft 11 is turned by a spring drive when clutch 9 is disengaged, to set the cam 6, the setting motor being dispensed with, Fig. 13 (not shown). An additional cam on the shaft 11 operates a switch after a predetermined net slewing movement to disengage the clutch 9 and prevent overstraining the spring, Fig. 14 (not shown).