OPEN-LOOP POSITIONING SYSTEM FOR ALPHANUMERIC DISPLAYS

摘要

A destination sign for buses is disclosed with an automatic positioning system for a plurality of sign modules. The sign is made up of plural modules, each of which is capable of displaying any one of a set of alphanumeric characters. The display of a module is changed from one character to another by displacement through successive equal angular increments. The positioning system comprises a reversible drive motor and a common shaft with a separate positioning clutch for coupling each display module to the shaft. The positioning clutch for each module is controlled by a command signal produced by a punch card reader and a shaft position encoder. Various words to be displayed by the sign are encoded on respective punch cards and insertion of a selected punch card into the card reader causes the positioning system to execute a reset cycle and a positioning cycle to display the selected name. Motor control means are connected with the encoder for energizing the motor in reverse direction to drive each module in the reset cycle to a home position and for energizing the motor in forward direction in the positioning cycle when the home position is reached. The encoder is connected with selector means including the reader to cause it to produce said command signal when the signal from the encoder bears a predetermined relation to the signal from the selector. Clutch control means are connected with the clutches and the selector and are responsive to the command signals for selectively engaging each of the clutches to couple the respective modules to the shaft during shaft displacement corresponding to the rotational distance between the home position and the position desired for the respective module as represented by the selector.