GB888480A - Improvements in machine tool control systems - Google Patents

Abstract

888,480. Electric copying machines; electric correspondence control systems. LANGHAM, E. M. May 6, 1958 [May 6, 1957], No. 14417/57. Classes 38 (6) and 40 (1). Co-ordinate movements of the table of a machine tool are controlled by the outputs of selected function generators of the kind in which the magnitude of the A.C. output signal is proportional to the desired function of the movement of an input shaft. The input shaft is driven by a closed loop system in accordance with the difference between actual table position and the desired position at the end of the cut, the latter being set in manually, or (in an unspecified manner) from the tape. The table itself is driven by another closed loop system in accordance with the difference between table position and the output of the selected function generator. An A.C. voltage whose magnitude is proportional to the position of the table along one axis is obtained from a measuring circuit WTA G , Fig. 7 (for details see below), and is connected in series with a voltage tapped off either of two potential dividers TVD 2 or TVD 5 . A voltage representing the first position to which the table is required to move is set by adjusting, manually or by a tape control, the tapping point on divider TVD 2 , so that an A.C. error voltage appears in the secondary of a summing transformer NT B . This voltage is applied via switch IS 1 , amplifier FGS A , rectifier FG R and limiters FG L , FG AL to a servomotor FG M , which by means of clutches C 1 . . . C 4 can be engaged to drive any one of four function generators CFG 1 , CFG 2 , LFG 1 , LFG 2 . The generators CFG 1 CFG 2 consist of resolvers by which the x and y co-ordinates of a circle are generated as the input shaft is rotated, and generators LFG 1 , LFG 2 consist of continuously variable auto-transformers by which the x and y co-ordinates of a straight line are produced as the input shaft is rotated. Assuming, for example, that the machine tool is to produce a straight cut from the starting point up to the first datum point set up on divider TVD 2 , then clutch C 4 will be selected-by hand or by tape-together with switches S 11 and S 11# -so that the linear function generator LFG 2 is driven by the motor FG M and its output is connected in series with the table position signal to the summing transformer NT A . The output of the transformer NT A energizes the lead screw motor LS A over switch IS 1 so that the table moves in accordance with the output of the function generator. When the table reaches the first datum point both motors stop. Meanwhile the next datum point has been set up on divider TVD 5 and the next function generator has been selected so that on changing- over switch IS 1 the next cut is made. The above equipment is duplicated in respect of the second axis of movement. Measurement of table, position.-An A.C. voltage is applied to two parallel connected voltage dividers TVD 1 and TVDx, Fig. 1, and the table position signal is the voltage between the tapping points of the dividers. Divider TVD 1 is for manual datum setting. Divider TVDx consists of a tapped inductance connected to a series of fixed contacts Rc spaced alongside the work-table (or around the periphery of a circular table, Fig. 3, not shown), so as to be contacted in turn by arms Ra mounted on the spindle of a sine resolver R of the kind disclosed in Specification 696,283, moving with the table. The resolver R has a four-phase rotor winding and a stator so wound that the amplitude of the signal in any rotor winding is proportional to the sine of the angle of rotation -away from a neutral point. Contacts on the arms Ra are connected respectively to the four rotor windings, the star point of which is the output tapping. A torque motor Tm holds the contact on each arm Ra firmly in turn against the fixed contacts Rc. The scale of the resolver output is arranged so that when two arms Ra are in contact with two fixed contacts Rc, e.m.f. balance is obtained. In a modification, Figs. 1B, 1C (not shown), two resolvers co-operate with interleaved fixed contacts, with automatic change-over switching to select the resolver that is not about to undergo transition from one fixed contact Ra to another. Specification 579,338 also is referred to.