SERVOMECHANISM INCLUDING A FEED RATE COMPARATOR FOR A FREQUENCY SIGNAL PROPORTIONAL TO SYSTEM ERROR WITH A PROGRAMMED FREQUENCY

摘要

A numerical control system having a pulse responsive servosystem for driving an object to an end point controls the velocity of the object by comparing a numerical representation of the position error with a numerical representation of a desired velocity of movement and developing a train of pulses having a rate proportional to the smaller numerical representation which is applied to the pulse responsive servosystem. As shown, movement instructions for machine parts 14-16 are encoded on a tape 17 which is read by a reader 18 decoded by a decoder 19 and charged into binary form by a translator 20. The output of the translator is fed to binary re-circulating command registers 23-25 allocated to the coordinate axes. The control arrangements for the axes are similar and for the X-axis the position of the machine part 14 is determined by an electrooptical quantizer 27 generating discrete pulses each indicative of unit axis movement. The quantizer pulses are fed to a binary re-circulating position register 31 and their sum compared with the contents of the command register 23 by comparator 34. The output of the comparator is applied to an error frequency generator 46 having a.pulse output which has a frequency proportional to the position error and is applied to one input of a frequency selector 43. The other input to selector is derived from a generator 40 the pulse output of which has a frequency proportional to the feedrate commanded by the tape. The selector 43 selects the lowest input pulse rate to control an X-axis servo 11 so that the machine part moves towards the commanded position at a constant feedrate until the position error falls to a value at which the pulse rate of generator 46 is below that of generator 40 after which the machine part is finally positioned at a feedrate proportional to position error. The commanded feedrate is derived from a clock oscillator 37 the output of which is applied to a binary frequency generator 38, comprising a counter chain of bi-stable multivibrators, providing a plurality of pulse trains that do not overlap. The pulse trains are fed through a manually adjustable feedrate control 39 to a generator 40 which multiplies the selected pulse train from control 39 by a number received from a storage register 19, set in dependence on the commanded feedrate by the translator 20.