Browse Prior Art Database

Distance Measuring

IP.com Disclosure Number: IPCOM000075921D
Original Publication Date: 1971-Dec-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 3 page(s) / 38K

Publishing Venue

IBM

Related People

Vermeulen, JC: AUTHOR

Abstract

In precision measuring systems with two-phase tachometers, it is desirable to have simplified electronic circuitry for precisely detecting direction and amount of travel. Such circuit is usable in either a rotary or linear system.

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Distance Measuring

In precision measuring systems with two-phase tachometers, it is desirable to have simplified electronic circuitry for precisely detecting direction and amount of travel. Such circuit is usable in either a rotary or linear system.

Two-phase tachometer supplies A and B pulses to resynchronizing delay 10. Resynchronizing delay 10 is important, in that the effectively random transitions of signals A and B are synchronized to the operation of logic circuits by clock 12. Direction and transition detection circuit 13 responds to the output signals of resynchronizing delay 10. Clock signals 01 and 02 time circuit 13 to actuate count steering latch LCS 14, to indicate direction of travel and to count the amount traveled in distance counter (DK) 15. LCS 14 determines direction of counting in up-down counter DK 15. The clock cycle from 00 through 03 is shorter than the duration of any one-half cycle of either pulses A or B.

First, the tachometer transitions are captured and stored in delay 10. At 00, latches LA1 and LB1 are actuated to capture and hold the signal conditions of A and B, respectively. LA1 and LB1 are so-called "phase-hold" latches of well- known design. The signal state of these latches represents the current signal status of signals A and B. At time 03, signal conditions of LA1 and LB1 are transferred to phase-hold latches LA2 and LB2, respectively. These two latches represent the signal state of signals A and B during the immediately preceding clock cycle. Differences in signal states between LA1 and LA2 or LB1 and LB2 indicate a transition.

Processing circuit 13 compares the previous signal conditions and the present signal conditions to detect direction of motion and to count distance. Processing circuit 13 counts all transitions in signal A when the illustrated switches are in position 1; counts all transitions in both signals A and B when the illustrated switches are in position 2; or counts only the negative transitions in signal A when the switches are in position 3. By providing further electrical interconnections within processing circuit 13, any selected set of transitions of signals A and B can be counted.

Exclusive-0R (gamma) circuits 1 and 2 compare the polarities of signals A and B for determining which transitions have occurred. Gamma 1 also determines the direction of motion and sets LCS 14, in accordance with the detected direction of motion. AND circuits A1 and A2 gate the output signals of Exclusive-OR circuits for counting and changing direction of the counting. A1 is responsive to the Exclusive-OR determinations to actuate phase-hold latch LCS 14 to accept the output signal of gamma 3. A2 is responsive at time 02 to increment or decrement DK 15 in accordance with the signal state of LCS 14.

For counting every transition in A, the direction of motion is first detected at
01. In this case, A1 is equal to the output of gamma 3 at time 01. Gamma 3 equals the Exclusive-OR function of LA2 wi...