US 4,789,874 AGranted

Single channel encoder system

AssigneeHewlett-Packard Company

InventorsMark W. Majette, William J. Walsh, John A. Wickeraad

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Abstract

A control system providing a control of position, velocity, and direction of movement of a member in an axis of freedom which employs a scale having scale divisions thereon and bands or zones defining limits of constant velocity control, acceleration and deceleration zone limits, and a rest or parking position. The scale spans and parallels the axis of freedom. A single channel transducer or encoder mounted on and moving with the member produces time varying output signals in response to the sensing of scale divisions along the scale and signals of different characteristic in response to encoder sensing of the limit bands. The time varying output signals are employed as scale division count signals for position determination and as scale division count signals per unit of time, for velocity feedback. The signals of different characteristic produced upon entering and during crossing of the limit bands, are utilized in a system of logic for computing control system signals to compensate control uncertainties in differing functional modes of the control system.

In a device having work element means movable along a path in an axis for performing a work function within predetermined limits of movement in said axis, motor means for driving said work element means and a control system for operating said motor means in response to work commands, the improvement comprising:

a stationary scale paralleling said axis;
equally spaced marks on said scale defining equal scale divisions along said scale;
a pair of work limit bands on said scale spaced from each other on said scale, each having a dimension along said scale greater than that of each of said marks;
a scale detector connected to and movable with said work element means adjacent said scale for detecting said marks and said work limit bands;
said detector producing a time varying voltage in traversing each mark and the space adjacent thereto along said scale;
said detector producing a work limit voltage different from said time varying voltage upon detection of a work limit band, said work limit voltage existing while said detector remains in said work limit band;
means connecting said scale detector to said control system to supply said time varying voltage and said work limit voltage thereto;
means in said control system responsive to said work commands for operating said motor means to move said work element means in said axis and said detector along said scale;
means in said control system responsive to a first work limit voltage of said detector while crossing a first of said work limit bands, to initiate a work function of said work element means upon the occurrence thereafter of a time varying voltage of said detector, and for terminating said work function of said work element means upon a second occurrence of said work limit voltage off said detector when said detector detects the other of said work limit bands;
a pair of sweep limit bands on said scale, each sweep limit band being disposed between a work limit band and the adjacent end of said scale and each having a dimension along said scale greater than that of each of said marks;
equally spaced marks on said scale between each work limit band and each sweep limit band, defining equal scale divisions therebetween;
said detector producing a sweep limit voltage different from said time varying voltage upon entering a sweep limit band;
and
means in said control system responsive to said second occurrence of said work limit voltage for operating said motor means to decelerate said work element means and to stop said work element means in said sweep limit band in response to the occurrence and existence of said sweep limit voltage when said detector detects said sweep limit band.

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Abstract

Claims17