Patent GB-875964-A (GB)
Title: An instrument for subtense surveying
Inventor: HAGLUND MATS
IPC: C08F2/00
Filed: 1957-10-18
Abstract: 875,964. Surveying instruments. TRAFIKAKTIEBOLAGET - GRANGESBERG - OXELOSUND, and LUOSSAVAARA - KURUNAVAARA A. B. Oct. 18, 1957. No. 32558/57. Class 97(2) The surveying instrument comprises a base having mounted thereon a levelling device and a telescope tiltable about a horizontal axis, there also being provided a slide which is movable parallel to the optical axis of the telescope through a distance depending on the degree of rotation of the telescope when the latter is moved through the angle subtended at the instrument by a staff normal to the line of sight so as to bring a part of a two dimensional scale into the field of view of a microscope in accordance with the displacement of the slide and so that the reduced distance between the instrument and the staff and the he:ght of the staff above the instrument can be read off. As shown, in Fig. 2, the instrument comprises a telescope 28a which is mounted in trunnions 28 in pedestals on a base 39, attachable to a tripod and provided with a spirit level. Over the base is placed a piece of paper 1 and in use a pin 56, Fig. 3, on a rider 41 is moved into the azimuth axis and caused to prick the paper by pressing in a button 56a. The instrument is sighted on the top of a staff normal to the line of sight by operating a knob 15, Figs. 2 and 3, engaging an arm 12 extending from a ring 10 which can be clamped to an inner ring 11 in which the trunnion 28 is journalled. Thereafter, a knob 16 is turned so as to rotate anti-clockwise a lever 18, Figs. 3 and 9, linked thereto by a rod 17a and a rack and pinion. Such movement of the lever 18 causes the telescope to be tilted downwards by a spring 20 disposed between an extension 90 on the side of the trunnion 28 and a bar 19 which is pivoted at 19a to the trunnion 28 and engages between an abutment 24 and a spring 23, both carried by an arm 25 on the ring 11. In order to bring the collimation axis accurately on to the bottom of the staff, a knob 26 is turned so that a screw 27 moves on a slide 21 so that an arm 22 thereon co-operates with the bar 19 so as to tilt the telescope upwards. A finer adjustment is provided by nut 29 which operates a screw 29a engaging a spring-loaded wedge 30 which moves the screw 27 bodily to the left or the right according to the direction of displacement of the wedge 30. The displacement of the slide 21 necessary to correctly sight the telescope is used to provide scale readings of the reduced and unreduced distances to the staff at the second surveying station. The unreduced distance is given by a scale 37, Fig. 5, carried by the slide 21 and illuminated from a lamp 57 via prisms 58, 59, the reading on this scale being projected via prisms 60-64 and a mirror 66 into a microscope 38; the angular displacement of the mirror 66 is halved by a gear train 67-71 so that the scale image remains in a fixed position during tilting of the telescope. A pin 35 on the slide 21 has a plate 33a journalled thereon and prevented from swivelling by a parallelogram linkage 34, Figs. 2 and 5, this plate carrying a scale 33 which gives the reduced distance to the staff. Scale 33 is illuminated by the lamp 57 via prisms 63a-63c and the light reflected from the scale 33 returns along the same path and thence through a parallel plate micrometer 72 into the microscope 38. The sheet of paper 1 is held down on the base 39 by springs 6, Fig. 3, acting on a ring 5, which can be lifted by turning a knob 2 actuating a worm 2a. This worm engages a ring 3 having pins 4 projecting through helical slots in the ring 5, rotation of which is prevented by pins projecting into the rim of the base. A ring 52 also serves to lift the ring 5, the ring 52 being mounted in a ring 55 having slots in which are carried three vertically movable straps with pins which project into helical slots in the ring 52. The rider 41 carrying the paper-pricking pin 56 is mounted for travel along a lead screw 40, Fig. 3 and is provided with a scale 79 which can be read in the microscope 38. This scale is joined to a rack 78 meshing with the smaller pinion 76 of a pair of pinions 75, 76 rigidly connected to a pin 74 on the rider 41, the pinion 75 meshing with a rack 77. The reduced distance read off the scale 33 is set on the scale 79 by operating a knob 44 on the lead screw 40 so that the pin 56 will prick the paper 1 at the right point. The rider 41 is also provided with pins 47, Fig. 5, which can be raised or lowered to engage or disengage the paper 1 by turning a knob 49a or 45a, these knobs being provided on coaxial screws 49, 45. The screw 49 engages a worm and a worm wheel 50 which is slidable on a splined shaft 51 bearing a pinion at one end meshing with teeth on the ring 52, this arrangement allowing the ring 5 to be raised by turning the knob 49a.