GB839847A - Error reduction by additional control in servo mechanisms - Google Patents

Abstract

839,847. Electric corresponttence control systems. HOLLANDSE SIGNAALAPPARATEN N.V. May 17, 1956, No. 15406/56. Class 40 (1). A correspondence control system for causing a receiving shaft to repeat the rotation of a transmitter shaft comprises two selsyn systems in cascade which act as LP filters to remove most of the noise content plus a proportion of the legal error signal, the latter being reintroduced by passing the misalignment signal of the first selsyn link, which will comprise both legal signal and noise, through a sharply tuned LP filter to remove the noise content, and feeding forward the remainder as an additional control signal to the second selsyn receiver. Alternatively when the mechanical servo links do not remove all the noise, the feed forward signal merely reduces the noise content. As shown (Fig. 1), the rotation of a transmitter shaft 101 attached to the A.C.-energized rotor winding 102 of a selsyn transmitter produces a misalignment signal from the receiver rotor winding 105 which is amplified at 117 to cause motor 107 to rotate shaft 106 and rotor winding 105 until shafts 106, 101 are realigned. The amplifier 117 is also fed with a ## or ## anti-hunting voltage from tachogenerator 108. The rotation of shaft 106 is transmitted via a second selsyn system to a shaft 113, the amplifier 123 for the motor 114 driving shaft 113 being fed with the misalignment signal from the second servo system, which has lost the noise and part of the legal signal from shaft 101, supplemented by the misalignment signal of the first servo system after the noise component only of the latter signal has been removed by a low-pass filter 120. A 6 or 6 anti-hunting voltage for the second selsyn link is obtained from tachogenerator 115. Hence the rotation of shaft 113 follows that of shaft 101 independently of any noise content in the value represented by the angular position of shaft 101. The correction signal for the second selsyn may be derived from the misalignment signal of the first selsyn by other means, e.g. from the tachogenerator 108, and may be applied to different forms of follow-up devices. If any modification of the misalignment signal occurs between the first and second selsyn systems, e.g. if rotor winding 109 of the second selsyn is driven by shaft 106 through an n: 1 gear, then the feed forward signal is modified in the same way, e.g. it is fed through an n: 1 step-up transformer. One embodiment (Fig. 3, not shown) shows the invention applied to a system for converting cartesian co-ordinates to polar co-ordinates. Specification 500,648 is referred to.