Patent GB-289706-A (GB)
Title: Electrically driven wood grinding and like apparatus
IPC: D21B1/06
Filed: 1927-09-30
Abstract: 289,706. Winkler, X., and Holtzmann et Cie Akt.-Ges., E. Sept. 30, 1927. Controllers, actuating; controllers with mercury contacts; systems for alternating-current motors only. - In an electrically-driven feed, more particularly for use with an electricallydriven wood-grinding apparatus, in which electric control means is provided for the feed-control motor so that the rate of feed is dependent upon the load on the main motor that drives the grindstone and the current in the circuit of the main motor is employed to operate apparatus for controlling the supply of current to the feed-control motor, a relay or other electromagnetic device is influenced by the current in the circuit of the main motor and acts in combination with a mercury chamber or its equivalent having a piston operated by the relay, the strength of the current through the feed-control motor circuit depending upon the position of the mercury in the chamber. Alternatively, a pressure system may be connected to the mercury chamber and be controlled by one or two valves operated by the relay. As shown in Fig. 1, the wood logs &c. in a, container 3 are forced against a grindstone 2, driven by an electric motor 1. by chain members 4 actuated by an electric motor 5. A step transformer is inserted in the circuit R, S, T supplying current to the main motor 1, and a rotary magnet 9 is connected with the transformer for the adjustment of the required load by means of a step-by-step rheostat 8. A resistance 10 is connected to the magnet 9. and on the shaft of the magnet is a retarding weight 11 connected to a piston 13 in the main chamber 19 of a mercury chamber 12 having a number of sub-chambers 15 in which are contacts 14. With no load on the motor 1, the current through the rheostat 8 is small, so that the magnet 9 is overcome by the weight 11 and the piston 13 is depressed, thereby short-circuiting the resistances 16 of the feed-motor circuit 6. The speed of the motor 5 is thus increased and the wood fed to the stone 2 more quickly, thereby increasing the load on the motor 1 and the current in the rheostat 8, so that the weight 11 is raised and the resistance 16 adjusted. In a modification, Fig. 2, a solenod 20 is provided in the secondary circuit 21 of a transformer in the circuit R, T, S of the main motor 1, and a variable resistance 30 is arranged in parallel with the solenoid. The control valve connected to the solenoid core is preferably a discharge and supply valve 22, 23 operating vertically in a cylinder 31 having supply and discharge pipes 26, 24 for pressure liquid and supply and discharge pipes 27, 25 communicating with one arm 28 of a vessel containing mercury, the other arm 32 containing a resistance 29 consisting of three spirals connected to the circuit of the feed-motor 5. Normally, the surface of the mercury in the arm 32 is just below the lower end of the resistance 29. When the pressure on the grindstone 2 falls, the control valve falls and allows water, oil, &c. to pass by the pipe 27 to the arm 28 of the mercury vessel, thereby raising the level of the mercury in the arm 32 and short circuiting a part of the resistance. The speed of the motor 5 then increases and the rate of feed correspondingly increases until the load on the main motor 1 has again reached the desired value. The control valve 22, 23 oscillates about its mean position and keeps the revolutions of the feedmotor 5 within such limits that the feed and the pressure of the wood on the grindstone are so regulated that the main motor 1 receives the required load. This position of the valve 22, 23 may be controlled by a speed regulator &c. when the grindstone is driven by a water or steam turbine &c.