Patent GB-711790-A (GB)
Title: Improvements in and relating to transmission dynamometers
IPC: G01L3/08
Filed: 1951-01-08
Abstract: 711,790. Optical pointers. BROWNHILL, F. D., and MILLINGEN, R. D. VAN. Dec. 19, 1951 [Jan. 8 1951], No. 499/51. Class 97(1) [Also in Groups XIX and XL(b)] A rotary transmission dynamometer comprises a pair of flanges 3, 5, carrying members 2 supporting mirrors 8, 9, 10, 11. The flange 3 is secured to the shaft 1 directly, and the flange 5 is secured to a tube 6 co-axial with the shaft 1 and secured to the shaft 1 by a flange 7 positioned along the shaft 1 remote from the flange 3. Thus the relative displacement of the flanges 3, 5 with respect to one another is a function of the torsion of the shaft 1 between the flanges 3 and 7. The mirrors 8, 9, 10, 11 are arranged in pairs one pair 8, 9 being carried on one member 2 and the other pair 10, 11 being carried on the other member 2. A beam of light is provided by a suitable lamp 16 and condenser 17 which is housed with a suitable transparent scale 13 and lens 15 in a casing 13. The beam of light is reflected by the four mirrors 8, 9, 10, 11 into a telescope 18, or in a modification, on to the photoelectric cell described below. When the shaft 1 is rotating the beam will fall on the telescope only once per revolution via the four mirrors as shown in Fig. 1. The illuminated scale Fig. 2, comprises an upper finely divided portion and a lower coarsely divided portion. The finely divided scale is observed in the telescope directly and the coarse portion or part of it via the box like path provided by the mirrors. The mirrors are set initially out of parallel in the plane of rotation so as to bring the reflected image of the uppermost or zero line of the coarsely divided scale portion to the zero line of the directly observed image of the finely divided scale portion. This also removes the reflected image of the finely divided scale portion from the field of view of the telescope. Increasing torque changes the angle between the associated mirrors, since they are connected to opposite ends of the shaft 1 and the zero line of the coarsely divided scale portion appears to move upwards over the finely divided scale portion the latter remaining stationary in the field of view, Fig. 2a shows the field of view of the telescope with the 300-400 section of the coarse scale superimposed over the fine. scale. In a modification shown in Fig. 3 the torque carrying and torque free members are reversed the latter being arranged inside the former. A hollow elastic shaft 1<SP>1</SP> carries a flange 2<SP>1</SP> rigidly bolted to an internal flange 3<SP>1</SP> integral with the shaft 1<SP>1</SP>. A bracket 41 is supported in anti-friction bushes 5<SP>1</SP> co-axial with the shaft 11 and is connected to the remote end of the shaft by means of a tube 6<SP>1</SP> and flange 7<SP>1</SP> integral with the shaft 1<SP>1</SP>. The body 2<SP>1</SP> carries a mirror 8<SP>1</SP> mounted in a holder 9<SP>1</SP> and held in place by a plug 9<SP>11</SP>, while the member 4<SP>1</SP> carries a mirror 10<SP>1</SP> mounted in a holder 11<SP>1</SP>. The centres of the mirrors 8<SP>1</SP>, 10<SP>1</SP> face each other substantially parallel to each other and are displaced about half their diameter apart. Ports 20<SP>1</SP>, 21<SP>1</SP> in the shaft 1<SP>1</SP> and in the body 2<SP>1</SP> allow light from the collinator 13<SP>1</SP> to reach the mirror 8<SP>1</SP> at an angle of 45 degrees and after reflection by the mirror 10<SP>1</SP> to emerge on the other side of the shaft 1<SP>1</SP> through the opposite ports 20<SP>1</SP>, 21<SP>1</SP> of the body 2<SP>1</SP> and enter a telescope 18<SP>1</SP> together with a direct beam of light passing directly through the ports 21<SP>1</SP> in the shaft 1<SP>1</SP> just beyond the end of the body 2<SP>1</SP> to form a direct image of the illuminated scale as in the previous example. If the collimator and telescope are mounted on a rotatable bracket so that they may be rotated together around the shaft, and the light source is illuminated only once per revolution by a pair of cam operated contacts a stroboscopic effect is produced enabling the operator to compare torsional deflections for particular angular positions to certain cyclic torque variations. In a further modification the collimator and telescope may be combined in one housing by means of a partially reflecting imrror 112, Fig. 7, at 45 degrees and a light source at right angles to the viewing axis. In a still further modification illustrated in Fig. 8 a photoelectric cell 124 may be arranged to give a reading on a meter 125 which varies with the torque. In this case two rectangular marks 117, 123, are arranged in the beam as shown so that with no torsional deflection maximum transmission of light is realized. As torsion takes place the deflection of the beam causes partial cut off of the mask 123 as shown in dotted outline in Fig. 8 causing a variation in reading of the meter 125.