Patent GB-882321-A (GB)
Title: Improvements in or relating to gyro stabilized attitude or horizon indicator systems
Inventor: TOMIZAWA HIRAKU
IPC: G01C19/44
Filed: 1957-11-26
Abstract: 882,321. Gyrovertical systems. TOKYO KOKU-KEIKI KABUSHIKI KAISHA. Nov. 26, 1957, No. 36858/57. Class 40 (1). A system for indicating deviations from the vertical comprises a free vertical gyro, a separate reference device responsive to gravitation, correction means for comparing the responses of these to give an output signal for operating an indicator, and means for comparing the response of the reference device with the output signal and controlling the correction means accordingly. Such a correction system minimises errors due to short-term inaccuracies in the reference device (e.g. caused by acceleration of the craft containing it) and long-term errors due to wandering of the gyro, and achieves this result without applying any precessing torque to the gyro. In Fig. 4 a reference transmitter 3 of the type described below in Fig. 9 forms arms of an A.C. bridge whose output signal goes via an amplifier 5 to a motor 6. The casing of the transmitter is moved in accordance with the indicator signal (by means described below) so that the bridge unbalance signal represents the difference between the angle of tilt and the indicator reading. The motor 6 drives, via reduction gearing, the stator 32 of a selsyn 29 whose rotor is attached to a vertical gyro 34. The stator output is fed to another selsyn 48 which operates the indicator 49, and also to a third selsyn 40 to provide the abovementioned feedback to the transmitter 3. The signal from the rotor 39 is amplified at 44 and drives a motor 45 which restores the rotor 39 to a null position and at the same time moves the casing of the transmitter 3 until the signal applied to the motor 6 falls to zero. To prevent excessive oscillation of the indicator, the signal from the transmitter to the selsyn 29 is limited to a predetermined amount, either by suitable design of the transmitter, or electrically in the amplifier 5, or by a speed-governor on the motor 6 or its associated gearing. The indication at 49 will thus be an average of the indications of the two instruments 3 and 34, and will be sensibly free from errors in each alone. If either instrument produces large errors at any particular time, it can be cut out and the indicator driven from the other instrument alone. Further compensation against known errors can be provided by arranging for the motor 6 to rotate faster in one direction than the other. In Fig. 6 (not shown) the feedback for the transmitter is to a selsyn which is interposed between the transmitter and the amplifier 5, and the indicator is driven from this same feedback link instead of via the selsyn 48. A simplification is shown in Fig. 7 where the selsyn 29 combines the comparing and feedback functions. The stator coils 32 are energized from the transmitter and the rotor 31 is turned by the vertical gyro 34. Any signal induced in the rotor is passed through amplifier 5 to the control motor 6 which turns the selsyn stator until the rotor output is zero. The indicator pointer 62 is attached to the selsyn stator. To prevent the whole indicator from moving with the gyro spin axis, which is inconvenient for the navigator, the indicator card may be driven from the selsyn stator and the pointer attached to the frame of the craft (Fig. 8, not shown). In Fig. 9 two gravitationalsensitive devices are provided to sense deviations of the craft about two mutually perpendicular axes. Each device consists of a circular tube 84, 94 containing a resistance wire which is partially immersed in mercury, the tubes being joined to a glove 99 by shafts 97, 97<SP>1</SP> so that the relative resistance on each side of the centre tap depends on the degree of tilt of the craft in the corresponding direction. The output signals of the devices are fed via amplifiers 82, 92 to motors 81, 91 which drive the stators of selsyns 78, 88 whose rotors are attached to the frames 74, 72 of a vertical gyro 76. The signals from the selsyn stators are fed to further selsyns 86, 96 which drive the frame 98 of the globe 99 into a null position when it will be horizontal, thus providing an artificial horizon. The angular position of this frame with respect to the craft will thus indicate the degree of tilt of the craft in the corresponding planes. The mercury transducers may be replaced by resistors or potentiometers whose moving contacts are controlled by gravitational pendulums, or by the device of Fig. 10 in which three fixed electrodes 113, 114, 115 are immersed in a conducting liquid and a pendulum rotates a movable electrode 112 to change the relative resistances of the paths.