LOCAL CONTROLLER FOR TRAFFIC CONTROL SYSTEM

• US 3,641,486 A
• Filed: 06/23/1969
• Issued: 02/08/1972
• Est. Priority Date: 06/23/1969
• Status: Expired due to Term

• Current Assignee: Mark IV Industries Corporation
• Original Assignee: Ludwig R. Pallat, Peter C. Brockett
• Inventors: Brockett, Peter C., Pallat, Ludwig R.
• Primary Examiner(s): Claffy, Kathleen H.
• Assistant Examiner(s): Myers, Randall P.
• Application Number:
  US04/835,343
• Time in Patent Office: 960 Days
• Field of Search: 340/35,37,40,41
• US Class Current: 340/913
• CPC Class Codes: G08G 1/082 Controlling the time between beginning of the same phase of a cycle at adjacent intersections

Abstract

A local controller for use in a traffic control system is provided with all solid-state means for displacing the local traffic cycle relative to a master traffic cycle and for effecting the smooth transition between alternate displacements. The traffic cycle length is determined by measuring the period between the phase coincidence of two signals having a slight difference in frequency.

Claims

1. In a local controller for use in a traffic control system of the type wherein the traffic cycle is defined by the time lapse between the phase coincidences of two signals having a slight difference in frequency, one of which, referred to as a cycle length signal, gradually shifts in phase with respect to the other referred to as a reference signal, the improvement comprising:

means responsive to the said reference signal adapted to trigger a ramp generator;

a ramp generator adapted to provide a sawtooth-shaped output, the frequency of which is identical to that of said reference signal;

means for converting said cycle length signal to a train of pulses corresponding in frequency to the frequency of said cycle length signal;

means for comparing the voltage level of the output of said ramp generator to the output of a variable voltage source and for generating an offset signal pulse each time the voltage of said ramp generator output reaches the level of the output of said variable voltage source;

a variable voltage source; and

means for determining the pulse coincidence of said offset signal pulses with said cycle length signal pulses whereby coincidence of said pulses defines the point within each traffic cycle bearing the same proportion to the total traffic cycle length that the output of the variable voltage source bears to the maximum DC level of the output of said ramp generator.

2. The invention in accordance with claim 1 wherein said reference signal and said cycle length signal comprise sinusoidal waves, said means for converting said cycle length signal to a pulse train comprises a sine wave to pulse converter, and said means responsive to said reference signal adapted to trigger said ramp generator comprises a second sine wave to pulse converter.

3. The invention in accordance with claim 1 wherein said variable voltage source comprises an operational amplifier and said local controller further comprises circuit means for gradually driving the output of said operational amplifier from its present offset voltage level toward a selected offset voltage level.

4. The invention in accordance with claim 3 wherein said driving means includes a positive input to said amplifier, a negative input to said amplifier, a switch shunted to ground across said positive input, a capacitor shunted across said amplifier, and means for closing said switch when said selected offset voltage level is higher than said present offset voltage level and for opening said switch when said present offset voltage level is higher than said selected offset voltage level whereby to gradually drive the output of said amplifier from said present offset voltage level to said selected offset voltage level.

5. The invention in accordance with claim 4 wherein said means for closing and opening said switch includes an offset selection circuit adapted to receive a selected one of a plurality of offset voltage levels lower than the maximum voltage of the ramp generator output, means for comparing the selected offset voltage level to the output of said ramp generator and to produce a signal when the output voltage of said generator builds to the DC level of sAid selected offset voltage level, and further means for comparing the output of said last-recited means with said offset signal pulse and for closing said switch if said signal leads said offset pulse and for opening said switch if said signal lags said offset signal pulse.

6. The invention in accordance with claim 5 wherein said further comparing means includes a delay multivibrator the duration of the output pulses of which are one-half the period of said reference wave energy, means for triggering said delay multivibrator when the output of said generator reaches the DC level of the output of said selection circuit, means for inverting the output of said delay multivibrator, flip-flop means having a '"'"''"'"''"'"''"'"'0'"'"''"'"''"'"''"'"' output adapted to close said switch and a '"'"''"'"''"'"''"'"'1'"'"''"'"''"'"''"'"' output adapted to open said switch, first gate means adapted to switch said flip-flop to a '"'"''"'"''"'"''"'"'1'"'"''"'"''"'"''"'"' state when the output of said delay multivibrator and offset signal pulse coincide and second gate means adapted to switch said flip-flop to a '"'"''"'"''"'"''"'"'0'"'"''"'"''"'"''"'"' state when the inverted output of said delay multivibrator and said offset signal pulse coincide.

7. The invention in accordance with claim 6 further comprising means for driving the output of said operational amplifier to zero from a maximum voltage value and means for driving the output of said operational amplifier to a maximum value from zero.

8. The invention in accordance with claim 7 wherein said means for driving the output of said operational amplifier to zero from a maximum voltage level comprises a switch shunted across said capacitor and gate means for closing said capacitor switch when said flip-flop is in the '"'"''"'"''"'"''"'"'0'"'"''"'"''"'"''"'"' state and said offset signal pulse and said reference signal sine wave to pulse converter output pulse coincide.

9. The invention in accordance with claim 7 wherein said means for driving the output of said operational amplifier to a maximum voltage value from zero comprises a negative voltage input to said amplifier and means for feeding said negative voltage input to said amplifier when said flip-flop is in the '"'"''"'"''"'"''"'"'1'"'"''"'"''"'"''"'"' state and said offset signal pulse and said reference signal sine wave to pulse converter output pulse coincide.