Patent GB-678469-A (GB)
Title: Improvements in or relating to a mechanism for translating motion
IPC: G08C21/00
Filed: 1950-03-31
Abstract: 678,469. Electric follow-up systems. CONSOLIDATED ELECTRIC CO. March 31, 1950. [April 2, 1949]. No. 8103/50. Class 40 (i). [Also in Group XXIV] In an electromechanical correspondence control system (e.g. for teleautographic transmission) wherein a motion produced by a transmitting member is resolved by a mechanical linkage into two independent co-ordinated motions, which are transmitted over separate channels and translated by a second mechanical linkage into a resultant motion of a receiving member (e.g. a stylus) over a surface, accurate coincidental follow-up without interference between one and the other co-ordinate motion is ensured by controlling the received motional component in each co-ordinate direction proportionately to the second time derivative of the corresponding transmitted component, and designing each linkage mechanically so that its mutual moment of inertia connecting the sources of co-ordinated motion is zero for any position of the combined motional member. Fig. 1 shows a tele-autographic system wherein a transmitting stylus 11 movable along X and Y co-ordinates of a writing surface 10 is connected through a pivoted parallelogram linkage 12 to modulate the frequencies of oscillators 13, 14 in correspondence with the. respective co-ordinate movements. The frequency modulated signals are transmitted by line or radio to a remote station and after, separation by filters 28, 29 and amplification. are supplied through respective discriminators to acceleration signal networks 33, 34 and positional correcting networks 20, 30 whereby unidirectional composite co-ordinate signals are produced proportional primarily to the accelerations of the transmitting stylus and secondarily to the positional errors between the transmitting and receiving styli, which after amplification at 35, 36 energize the moving coils.37, 38 of permanent magnet galvanometric units 39, 41. The coil deflections are mechanically connected through a further parallelogram linkage 46 to a stylus 45 moving over a writing surface 44 supplied with a continuously moving paper strip. Linkages 56, 57 operate movable elements in the positional correcting networks 20, 30 in accordance with the co-ordinate movements of the receiver stylus so that the networks produce the appropriate error signals. Fig. 6 shows the receiver linkage, in which the stylus 45 is carried by an arm 47 having a balance weight 89 at the other end and pivoted to yokes 72, 74 carried by parallel arms 51, 48. Arm 48 is rotatable about a fixed pivot 49 and carries a collinear extension 73 which is linked to the first galvanometer coil 37 while the arm 51 is pivoted at yoke 81 to an arm 52 forming the remaining side of the parallelogram, which is connected to a rotary shaft 53 collinear with the pivot 49 and carrying a further arm 78 linked to the second galvanometer coil 38. To ensure accurate correspondence between the movements of the transmitter and receiver styli, the linkages must be such that movements in one co-ordinate direction do not introduce spurious movements in the other direction, and the masses of the several arms are so chosen and distributed that the torque applied to arm 48 is zero when arm 52 is rotated, and the torque applied to arm 52 is zero when arm 48 is rotated. Thus for either driving arm, # MXY=0 (where M denotes mass and X, Y its rectangular co-ordinates) when the other arm is accelerated, i.e., the moment of mutual inertia between the arms is zero. Fig. 8 shows the mass distribution of a parallelogram linkage in which m1 represents the stylus weight, m2 the balance weight, and m3, m4 the weights of arms 47 and 51. Assuming the co-ordinate axes to be 48, 52, the mass co-ordinates to be as indicated and X1., Y4 to be the lengths of the parallelogram sides, the relation m1 X1 Y1 + m2 XI Y2 + m3 X1 Y3 + m4 X4 Y4=0 must hold for the system. The distributed masses must have no substantial dimensions laterally of the parallelogram members, and their co-ordinates must remain unaltered as the arms are rotated. This construction also eliminates interaction errors due to the centrifugal forces developed by the several velocities of the mass elements during acceleration. A mathematical analysis is given.