Patent GB-1353171-A (GB)
Title: Control system for magnetic positioning device
IPC: G05B19/40
Filed: 1971-04-29
Abstract: 1353171 Control of A.C. motors XYNETICS Inc 29 April 1971 [11 May 1970] 12211/71 Heading H2J [Also in Division G4] Apparatus for controlling a linear motor comprising a magnetic head and a ferromagnetic slotted plate by means of digital signals comprises means generating a pulse train of a length determined by the digital signals, this train having short bursts of pulses superimposed thereon at particular points to provide for acceleration and deceleration of the head, the pulse train being adapted in a D/A converter to produce a sin-cos signal of a phase angle relative to magnetic vector of the plate at the head position to produce the required forces of movement. As shown digital inputs Nx, Ny are derived from a store and are taken to x and y registers 102, 104 together with sign bits to control switches 106, 108, 114. The stored signals are compared at 110 and divided at 116, the numerically greater, Nx or Ny, being fed via switch 112 to set a counter 120, a number K<1 being produced at 116. The number set at 120 is fed as input to a velocity control circuit, 122, (also see Fig. 5, not shown) together with a number Na set at 124, 126. A positioning operation is started with an input a at 139 starting a suitably adjusted ramp generator 132 adapted to control the frequency. of a pulse generator 148, pulses being gated at 150 by the setting of a flip-flop 136 by the start signal a, which signal also, via gate 130, sets flip-flop 170 to gate pulses at 168 from a high frequency source to a counter 166 adapted to pass a preset number Nb of clock pulses, comparator 164 causing re-setting at 170 upon this number being reached. The pulses from 148, 150 are placed on two lines, and the signal at 156 representing the smaller of Nx Ny displacements is multiplied by the number K to ensure a correct vectorial positioning of the head occurs, the frequencies of the pulse trains being divided at 154, 158 and these signals superimposed at 182, 184 with the burst of pulses from counter 166. The composite signals are taken to corresponding registers 190, 192 and converted at 14, 16 to sin-cos signals applied to respective coils 202-208 in the head assembly to move the head along both x and y axes to obtain a vectorial displacement. The number Nb is adjusted to provide a phase angle between the coils field vector and the magnetic plate field vector to effect the required acceleration. Pulses from gate 152 are caused to count down the contents at 120 and after the predetermined Na number, a signal b is emitted to derive a second burst of pulses applied via the enabling of gate 128 through gates 172, 180. A deceleration is produced and a "hold" signal is simultaneously applied at 132 and the head member is driven at constant velocity until the occurrence of a signal c causing a further decelerate burst via gates 172, 180 and a "down" signal to be applied to the ramp generator 132. At a count of Na prior to the end of the desired motion, a signal d causes stopping of the pulses at 152 &c. by disabling of gate 150 via flip-flop 136, and an accelerate burst to occur to bring the head to rest. In the event of a very short distance to be moved (e.g. Na#20) the generator 148 and counter 166 &c. are overridden and a fixed frequency generator 138 is employed.