Digital position measuring devices

Claim 1

A digital position measuring device for measuring the displacement of a member movable relative to a fixed member along an axis having a series of zero positions thereon successively and equally displaced one from the other therealong to form a series of steps corresponding to said zero positions, comprising: first digital counter means for digitally registering the relative position of said movable member within one of said steps, said first counter means having a maximum count of a value equal to a value corresponding to the displacement along said axis between an adjoining pair of said zero positions, converter means for converting the digital content of said first digital counter into a corresponding analog signal, second digital counter means for counting concurrently with said first digital counter means, said second counter means having a maximum count of a value at least equal to the value corresponding to the displacement between three adjoining ones of said zero positions, visual display means connected to said second counter means for displaying the digital contents of the second counter means, a source of counting pulses, position detecter means responsive to said analog signal from said converter means to supply a corresponding error signal, control means operative in response to said error signal for controlling the transmission of counting pulses to said first digital counter and concurrently to said second digital counter, and zero reset means for maintaining the digital contents of said first and second digital counters at a zero value for the duration of a transient period which occurs when said digital position measuring device is switched on for subsequently starting the counting operation thereof to provide a representation on the visual digital display device of the relative position of the movable member within the limits of one of said steps.