Patent GB-960581-A (GB)
Title: Improvements in or relating to control mechanism
Inventor: WESTON BENNETT
IPC: G01F11/00
Filed: 1959-08-27
Abstract: 960,581. Gearing for stopping and starting machinery; clutch-brake combinations; friction clutches. H. & B. PRECISION ENGINEERS Ltd. Nov. 24, 1960 [Aug. 27, 1959], No. 29377/59. Headings F2C and F2L. In an operation or process timing device using a constant speed drive cr, as shown, in apparatus delivering predetermined quantities of powders or granular materials, means adjustably controlling the extent of rotation of a rotary machine element such asa delivery screw (not shown), which is rotatable in a cylindrical outlet 12 (Fig. 1), and driven by an electric motor 84 through a V-belt drive 90, 92 and clutch members of an electromagnetic clutch/brake 50, 34, 14, comprises a stiff, straight, piano wire rod 128 (Figs. 3, 6), which on energization of said clutch at the start of a machine cycle is engaged, by means of a solenoid 162, with a V-groove 120 of a hardened pulley portion of a shaft 96 geared to the clutch driving member 50 and is axially moved thereby until its leading end actuates switch means to interrupt energization of the clutch and the solenoid 162 thereby respectively causing the screw to be braked and releasing the rod which is then returned to its starting position by a spring 130. The delivery screw is interchangeably mounted by its stem 27 in a collar 26 at the lower end of a spindle 20. The clutch/ brake comprises a driven member 34 connected to the screw spindle 20 by three axial pins 33 permitting vertical movement of the member 34, a driving member 50 integral with the driven V-belt pulley 92, a U-sectioned stationary electromagnet 42 having a coil 46, and a brake disc 14 integral with the machine frame. The parts 34, 42 and 50 are of high permeability cast iron. One or both of the mating surfaces of both the clutch and the brake may have facings or inserts of friction material such as vulcanized fibre, or an annulus of such material may lie between them. To minimize unwanted eddy currents and secure more rapid operation, the driving and driven clutch members 50, 34 and the stationary magnet 42 may have radial slots. The brake is actuated by the weight of the driven member 34 supplemented by an adjustable spring 78 acting through a rod 72 and balls 74 housed in a fixed shaft 60 which supports the clutch driving member 50 and, for clutch adjustment, may be vertically screwed and locked in a frame comprising upper and lower plates 62, 64. The shaft 96 is an intermediate shaft in a gear drive 54, 94, 98, 100 from the clutch driving member 50 to stirring rods 110, 112. The rod 128 is guided in tubes 122, 124 arranged in line adjacent the plate 64 and respectively in front of and behind the V-groove 120 in the shaft 96. The front tube 122 has a longitudinal slot 126 on its side remote from the plate 64. The rod 128 is urged rearwardly by the spring 130 and passes tangentially through the V-groove 120. A carriage 150, riding on a lead screw 136 and guided by a lateral blade 152 engaging the slot 126 in the front tube 122 has an insulated brush 154 which bears upon a D.C. supply-connected rod 148 carried in insulated bushes 144, 146 and communicates with an insulated contact 156 coacting with a spring contact blade 158 also connected to the carriage to complete a connection from the rod 148 to the machine frame via the carriage and the lead screw. An extension 160 of the blade 158 projects into the slot 126 a little behind the blade 152. When the rod 128 is moved forwardly a button 134 thereon abuts the extension 160 and breaks contact between the contact 156 and the blade 158. The amount of forward movement permitted the rod 128 before this contact-breaking takes place is determined by the longitudinal position of the carriage which is controlled by an adjustable knob 142, fixed to the lead screw, and indicated by means such as a calibrated band or tape 180 which is carried on flanged pulleys 182 and attached at one end to the carriage and at the other end to a tension spring 184. The solenoid 162 mounted on the plate 64 has an armature 164 mounted on a rocker 168 carrying a ball race 170 which is close to the V-groove 120 and on energization of the solenoid grips the rod 128 against the groove. The rotation of the shaft 96 is such that when the rod is gripped the rod 128 is fed forwardly against the spring 130. The energization of the solenoid 164 also closes two pairs of contacts 172, 174. A further pair of contacts 176 at the rear end of the tube 124 are held closed by a further button 132 on the rod 128 when the latter is in its normal rearward position. In operation, assuming the motor 84 running, closure of a trip switch 178 completes a circuit from one D.C. supply terminal through the solenoid 162, said trip switch 178, the contacts 176, the machine frame, the contacts 158, 156, the brush 154 and the rod 148 to the other supply terminal. The solenoid 162 operates to effect gripping of the rod 128, and to close the contacts 172, 174 which respectively hold energization of the solenoid and energize the clutch coil 46 to cause the delivery screw to rotate. As the rod 128 commences to move, the contacts 176 of the trip circuit are opened to prevent premature re-operation of the latter between completion of a delivery and the full return of the rod which re-operation would result in a short subsequent delivery. The delivery screw continues to rotate until the leading end of the rod 128 disconnects the blade 158 from the contacts 156 thereby releasing the solenoid 162 and stopping the delivery screw. The rod 128 then returns to its initial position and closes contacts 176 in readiness for a further operation of the trip switch 178 which may be actuated manually at will, or automatically by a cam on a machine with which the deliveries must be synchronized, or may remain closed for automatically repeated delivery cycles. The carriage position may be adjusted without stopping the machine.