Patent GB-1014933-A (GB)
Title: Electrical device for precisely positioning a remote component
IPC: G05D3/14
Filed: 1962-11-30
Abstract: 1,014,933. Electric correspondence control systems. ELECTRICITE, MECANIQUE ET APPLICATIONS. Nov. 30, 1962 [Dec. 1, 1961; Nov. 23, 1962], No. 45337/62. Headings G1N and G1U. In an electrical device for positioning a remote component, of the type in which an error signal from a bridge circuit is removed by rebalancing the bridge using a D.C. servomotor which also drives the component to be positioned, hunting is prevented by connecting a resistor in the bridge measuring diagonal, the resistor being traversed by a current dependent upon the armature voltage of the servomotor, an element having a non-linear current voltage characteristic also being connected so as to be traversed by the armature current. The sliders 2, 4 of potentiometers 1, 3 are coupled respectively, to the controlling and controlled elements 100,116, centre taps on the potentiometers being joined to the centre point of battery 102 to form a double measuring bridge. The output of an error detector 107 in the common measuring diagonal of the bridges operates one of two relays 103,104. The armature 5 of motor 6 is connected through reversing contacts 103a, 104a to rectifier 105. When neither relay 103,104 is energized the armature is short circuited for braking. The primary of a transformer 115 connected across the input terminals of rectifier 105 senses the armature voltage of motor 6 and a corresponding current is passed through rectifier 112, reversing contacts 103b, 104b, and non-linear resistor 114 to potential divider 108, 111. When lever 100 is moved the bridge is unbalanced and either relay 103 or 104 is energized to drive motor 6 in a direction to rebalance the bridge. The error signal is however opposed, through resistor 108, by a signal dependent upon the armature voltage so that the bridge balances before true correspondence is attained. Relay 103 or 104 is then de-energized and the motor is braked, coming to rest at the position of true correspondence. Resistor 114 takes account of non-linearities in variation in braking distance with armature voltage at the instant of braking. If the resisting torque on the servomotor is very variable a current dependent upon the armature current may also be made to pass through resistor 108 by connecting a further transformer across a resistor in series with the input to rectifier 105, the secondary of this transformer being in series opposition with that of transformer 115. In a modification (Fig. 3, not shown) resistor 108 may be connected in series with a non-linear resistor directly across the armature terminals, a further resistor being connected in series with the armature. In a similar arrangement (Fig. 4) greater sensitivity is provided near the centre regions of potentiometers 1, 3. Sliders 32, 33 on rotary contacts 34, 35 are coupled to sliders 2, 4 so that near the centre regions a relay 22 is energized. This opens contact 22a to reduce the speed of motor 6 and to change over switch 22b to short circuit resistor 27 and introduce variable resistor 40. Resistor 40 is preset to take account of friction in the motor at low speeds. The non-linear element may be a pair of Zener diodes.