Browse Prior Art Database

Bidirectional Position Encoder

IP.com Disclosure Number: IPCOM000075419D
Original Publication Date: 1971-Sep-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 3 page(s) / 51K

Publishing Venue

IBM

Related People

Elliott, JE: AUTHOR

Abstract

Positional encoders are used to detect angular position of a shaft or linear position of a moving member. This particular encoder utilizes two tracks for monitoring movement. The tracks may be optically or magnetically read. Signals transduced from the tracks are shown in Fig. 1. Track A is the incremental track and would be monitored by two separately positioned transducers. The separate positioning of the transducers provides a phase difference between the transducers so that the direction of motion, in addition to the distance, may be detected.

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Bidirectional Position Encoder

Positional encoders are used to detect angular position of a shaft or linear position of a moving member. This particular encoder utilizes two tracks for monitoring movement. The tracks may be optically or magnetically read. Signals transduced from the tracks are shown in Fig. 1. Track A is the incremental track and would be monitored by two separately positioned transducers. The separate positioning of the transducers provides a phase difference between the transducers so that the direction of motion, in addition to the distance, may be detected.

Track B is a reference track containing absolute reference position in a serial code. The code in the reference track is bidirectional so that the reference position may be detected as the moving member moves in either direction.

The bidirectional code is made up of a 1-bit indicating the start of code followed by the position data, followed by a 1-bit indicating center of code, followed by position data, and terminated with another 1-bit. The two sections of position data are mirror image in the binary order of bits but not in the numeric information they represent. As to numeric information, the second half is always one numerical value lower than the first half of the bidirectional code.

For example, the first half of the bidirectional code might represent the decimal value 6, while the second half of the bidirectional position data might represent the decimal value 5. The 6 may be read in the conventional left to right manner, whereas the 5 must be read in a reverse right to left manner. Obviously, the positional data when moving from left to right is 6, and the positional data when moving from right to left is 5. These values, in each case, represent the position that is about to be entered. The position data sensed is gated out during the incremental sample pulse 10, which occurs during the center 1-bit of the bidirectional code.

In Fig. 2, apparatus for interpreting the bidirectional code is shown. Incremental pulse signals arrive at the control logic 11 over lines 12 and 14. Position data from the reference track arrives over line 16. For each incremental pulse, a shift pulse from the control logic is derived and applied to the assembly register 18 via AND gate 20. This shift pulse is gated by AND gate 20 so that it is applied to the register 18 until the assembly register is filled with position data. When the position data in a reference track is encountered, it is loaded into register 18 from line 16 via AND gate 22 serially by the shift pulses.

To detect that position data has been completely loaded into the assembly register, the last stage of the register 18 is monitored for a binary 1. If the mode of operation is verify off, then the centermost 1 in the reference track position data will enable AND gate 22 at the same time that the first 1-bit, now in the last stage of register 18, conditions AND gate 24 to generate a signal indicating assemb...