The Secretary of State for Industry in Her Britannic Majesty's

Andrew George Hay

Peter R Mason

Position detecting apparatus having a target comprising radiation emitting eans for emitting radiation to define four points in non-planar relationship such that a first set of three of the points lies in a first target plane while a second set of three of the points lies in a second target plane which may for example be substantially normal to the first target plane; a camera having a focal plane on which images of objects presented to the camera are formed, the camera being arranged for viewing said target, and being provided at said focal plane with a two-dimensional array of photo sensitive elements which can receive radiation from the radiation emitting means of the said target; and a computer arranged to scan said two dimensional array to generate signals indicative of the position of images of the radiation emitting means on the array, whereby the position of the target, and hence of an object to which it is attached, may be determined in relation to a selected reference plane.

Position detecting apparatus

The invention provides a hydraulically-driven reciprocatory tool comprising piston with a shoulder reciprocable in a cylinder, and a shuttle valve for controlling supply of fluid to a first face of the piston, the fluid producing a force on the first face which is alternately greater than and less than a constant bias force applied to a second face of the piston, wherein the position of the shuttle valve is determined by the pressure of fluid in a fluid connection between the shuttle valve and first and second ports in the wall of the cylinder, the fluid connection including a first non-return valve for preventing flow of fluid from one of the ports to the shuttle valve and a second non-return valve for preventing flow of fluid from the shuttle valve to the other of the ports. Preferably, each non-return valve has associated with it a variable throttle in the fluid connection and further means are provided for controllable flow of fluid along a branch of the fluid connection.

Switching mechanism

The disclosure concerns a hydraulically driven impactor in which the operng cycle of a reciprocating piston is determined by the retraction velocity and displacement of the piston itself. Energy is conserved and heat dissipation minimised by the utilization of hydraulic spring accumulators to decelerate the piston. The drive to the piston is switched into a forward direction at such a point in each displacement cycle that the rebound energy of the piston is always re-absorbed into the drive fluid. The impactor operates at optimum acceleration and frequency at all times, whether or not impact occurs, and this feature combined with high energy conservation makes the impactor particularly suitable for use in a full-face tunnelling machine where high power density is required and individual impactors are often constrained to operate without impacting the rock face for considerable periods.

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Hamilton, United Kingdom

Andrew George Hay