GB903882A - Improvements in or relating to pruning-shears - Google Patents

Abstract

903,882. Pruning shears. TAUBE, G. Oct. 24, 1960 [Oct. 23, 1959; Sept. 22, 1960], No. 36434/60. Class 6(2). Mechanical pruning shears comprise a hollow casing supporting two pivoted blades, at least one of which is driven by a cam, integral with but eccentric to a tangent wheel, the latter being driven by a worm mounted on a shaft which is in turn driven from a motor via a clutch mechanism. The shears may comprise a pair of blades 60, 61, each formed with a slot 58, 59 respectively, and with an elongated portion pivoted respectively at 64, 65 on levers 66, 67 which are free to pivot about a spindle 68 fixed to the casing 1. The levers 66, 67 are extended rearwards beyond the pivots 64, 65, these rearward extensions being normally held apart by a sping 72. The slots 58, 59 are engaged by cams eccentrically mounted on tangent wheels 52, 53 which are rotated by a worm 51 on the shaft 5, the latter being driven from a motor via a clutch mechanism to be described below. The spring 72 allows the baldes and levers 66, 67 to pivot about the spindle 68 when an obstruction is encountered. Alternatively, as shown in Fig. 4, only one blade 80 is reciprocated by a cam, the other balde 83 being pivotable about the point 84 when an obstruction is encountered but normally held stationary by a spring 86 pressing a rearward extension of the blade against the casing 1. The clutch mechanism for both the forgoing embodiments is housed in a hollow extension 2 of the casing 1 and comprises firstly a tubular race 20 in driving engagement with a shaft 4 which is continuously driven from the output shaft of a motor, and secondly a bushing 14 screwed on to the shaft 5 which operates the blades of the device. The shaft 4 and tubular race 20 project into the bushing 14, the free end of the shaft 4 being formed with flattened portions 15, 16 which, when the baldes are inoperative, register with rollers 17 and 18 housed in slots in the race 20. Thus the shaft 4 and race 20 can then rotate relative to the bushing 14, which will remain stationary. In order to transmit drive to the bushing 14 and thence to the shaft 5, it is necessary to rotate the shaft 4 slightly, relative to the race 20, thus wedging the rollers 17 and 18 between the thicker portion of the shaft 4 and the bushing 14, so that the latter rotates with the shaft 4, This slight relative rotation is effected as follows:- the shaft 4 is in driving connection with the race 20 by means of a spindle 23 on the former engaging sloping ramps 24, 25 at the lower end of the latter. Midway along its length, the race 20 is embraced by a fork 26 which can be pivoted up or down by means of a spring-controlled rod 35 actuated by a trigger 50. As the fork moves up and down, it moves the race along the shaft 4, and the cooperation of the sloping surfaces 24, 25 with the spindle 23 during such up and down movement causes the relative movement between the shaft 4 and the race needed to operate the clutch. Fig. 4 illustrates a ratchet and pawl mechanism 95, 96 operative between the blade and the rod 35 to ensure that the blades always return to their open condition when the clutch is disengaged.