Patent GB-1025770-A (GB)
Title: Tilt limiting arrangement for a mechanical element
IPC: G08C21/00
Filed: 1963-07-11
Abstract: 1,025,770. Automatic stereo mapping system. THOMPSON RAMO WOOLDRIDGE Inc July 11, 1963 [July 16, 1962], No. 27578/63. Heading H4D. [Also in Division G1] Apparatus for limiting the tilt of a novable element which is transversely movable in a given plane and rotatable about an axis in the said plane, comprising means for controlling the tilt of the element in accordance with derived errors signals, two sensors coupled to the element and adapted to supply signals indicating respectively the rotational position and the transverse position to threshold means whose output signals cause the tilt control means to be disabled upon the recurrence of signals from the sensors in excess of predetermined threshold levels. The invention is particularly described as being used to control the tilt of a Nipkow scanning disc in a stereomapping system as described in Specification 1,025,769. The said system comprises, Figs. 1 and 2, a rotating Nipkow scanning disc 14 mounted in a carriage 12 which is moved along X and Y directions such as to scan in a television manner (see Fig. 2) through a stereo image produced by a pair of stereo photographs 24 and projecting light sources 22. The Nipkow disc is also mounted to rotate about a horizontal axis in the Y-direction such that it ideally always lies parallel to the terrain surface represented by the stereo image. The amount of such rotation on tilt of the disc is limited, however, by two factors:-(a) obstruction by elements beneath the disc, such as the two photo-multiplier tubes 26 and 27. This gives a constant positive or negative maximum value of the tilt angle #y, and (b) the fact that light can only pass from a light source to a respective photo-multiplier tube through the holes provided in the Nipkow disc for a limited range of tilt angles. This range is dependent on the position of the Nipkow disc in the X- direction. The control arrangement for limiting the tilt of the disc is shown in Fig. 4 and comprises the carriage 12 and disc 14 and the two photo-multipliers delivering output signals P1 and P2 to a tilt error signal generator 34, which compares the tilt of the disc with the slope of the scanned terrain and produces an error signal to align the disc, the error signal being applied via switch 36. The disc is connected to the wiper of a centre-earthed potentiometer 42, which delivers a D.C. signal indicating the tilt angle #y by magnitude and sign. This signal is fed to two threshold devices 52 and 53, which deliver a control signal to an OR circuit 59, when the signal indicates that angle #y has reached the limit set by factor (a) above. The OR circuit then passes the control signals to open switch 36 and stop further increase of the angle #y. The carriage 12 is connected to the wiper of a centre-tapped potentiometer 44, which, delivers a D.C. signal indicating the position X-direction. The signal is fed to a scanning circuit 46, together with the signal representing the angle #y. The scanning circuit then delivers a signal representing #y+kX to threshold circuits 56 and 57. The increase of the numerical value of this control signal above a certain value set in the threshold circuits indicates that the limit to #y set by factor (b) above has been reached. The appropriate threshold circuit then passes a control signal via the OR circuit 59 to open switch 36. In addition the A.C. tilt error signal is converted to a D.C. signal in detector 38 having a magnitude and polarity representing the magnitude and sense of the tilt error. The signal is fed to two threshold circuits 62 and 63 such that if after switch 36 has been opened the tilt error signal is such as would cause the tilt angle to decrease below the limit, a signal is produced by threshold circuits 62 or 63, depending respectively on whether the tilt error signal is in a positive or a negative sense. When the disc is locked in the negative direction a signal from the threshold circuit 62, caused by a positive tilt error signal, is fed to over-ride the signal controlling the negative threshold circuits 53 on 57. The signal from the particular one of the said threshold circuits, opening switch 36 is therefore cancelled and the disc is forced to move with the permitted range. A similar procedure occurs when the disc is locked in the positive direction and a negative tilt error signal occurs.