Control system for automatic guided vehicles

• US 4,811,229 A
• Filed: 01/05/1987
• Issued: 03/07/1989
• Est. Priority Date: 01/05/1987
• Status: Expired due to Fees

• Current Assignee: Hewlett-Packard Company (HP Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Wilson, Richard A.
• Primary Examiner(s): Chin, Gary
• Application Number:
  US07/000,500
• Time in Patent Office: 792 Days
• Field of Search: 364/424, 180/167-169, 901/1, 250/202
• US Class Current: 701/25
• CPC Class Codes: G05D 1/0242 using non-visible light signals, e.g. IR or UV signals
• CPC Class Codes: G05D 1/0244 using reflecting strips

Abstract

A control system for guiding a vehicle over a floor. The system includes a narrow length of retroflective tape applied to the floor to define a path, an array of LED-phototransistor sensors to generate light toward the tape and generate sensor output signals proportional to the portion of the sensor fields of view occupied by the retroreflective tape. The output signal of each of the sensors is compared to a stair-step reference signal during a 10 millisecond cyclic time period and a binary output signal for each sensor is generated indicating whether the amplitude of the sensor output signal is above or below the changing threshold reference signal. The binary value of each of the sensor output signals is sampled once each millisecond during the time period and the binary values are combined to generate a byte for each sampling occasion. Each of the bytes corresponds to a location in a lookup table which includes interim vehicle lateral directional and displacement commands. The commands corresponding to each of the table location values generated during the 10 millisecond period are mathematically summed to generate a final vehicle command. Two lookup tables are provided for selectively following the left or right edge of the tape.

Claims

1. A control system for guiding a vehicle over a floor along a long, narrow stripe of reflective material applied to the floor to define a desired path for the vehicle to travel, comprising:

means for generating light and directing said light toward the reflective material;

a generally linear array of light sensors mountable on the vehicle generally transverse to the stripe of reflective material, each sensor having a field of view and generating an output signal generally proportional to the portion of the sensor'"'"'s field of view occupied by the reflective material;

reference signal means for generating a reference signal with an amplitude generally unidirectionally and progressively changing over a preselected time period;

means for comparing each of said sensor output signals to said reference signal during said preselected time period, and generating a binary output signal having binary states for each of said sensors, said binary output signal in one binary state indicating if the amplitude of said sensor output signal is above said reference signal and in the other binary state indicating if the amplitude of said sensor output signal is below said reference signal;

means for sampling the value of each of said sensor binary output signals on a plurality of sampling occasions during said preselected time period and combining said sampled values of said sensor binary output signals for each sampling occasion in a predetermined order to generate a byte;

value determining means for providing for each said byte a corresponding position indicating value indicative of the lateral position of said sensor array relative to the reflective material at the time of said sampling occasion based upon the changing threshold provided by said reference signal; and

summing means for mathematically summing all said position indicating values for said one preselected time period and generating a vehicle command comprising a vehicle lateral directional command to control the direction of lateral movement of the vehicle as it travels along the path and a vehicle lateral displacement command to control the amount of lateral movement of the vehicle as it travels along the path.

2. The control system of claim 1 wherein each of said bytes generated during said preselected time period comprises a corresponding table location value, and said value determining means includes:

a look-up table storing a plurality of said position indicating values, each position indicating value being stored at a table location corresponding to one of said table location values, each said position indicating value comprising a vehicle lateral directional command component indicative of the amount of lateral movement of the vehicle required to travel along the path, and a vehicle lateral displacement command component indicative of the amount of lateral movement of the vehicle required to travel along the path, said vehicle directional and displacement command components being based upon the lateral position of said sensor array relative to said reflective material at the time of said sampling occasion corresponding to each of said bytes as measured using the changing threshold provided by said reference signal; and

look-up means for looking up ones of said position indicating values stored in said look-up table at said table locations corresponding to said table location values.

3. The control system of claim 2 wherein said look-up table includes a first table storing a first plurality of said position indicating values, each comprising one of said vehicle directional and displacement command components directing the vehicle to follow the left edge of the reflective material, and a second table storing a second plurality of said position indicating values, each comprising one of each of said vehicle directional and displacement command components directing the vehicle to follow the right edge of the reflective material.

4. The control system of claim 3, further including:

selection means for selecting whether the vehicle is to follow the left or right edge of the reflective material in response to instruction to the control system; and

means responsive to said selection means for causing said look-up means to look up said position indicating value at said table location in the one of said first or second tables corresponding to the left or right edge selected by said selecting means for the vehicle to follow.

5. The control system of claim 3 wherein said reference signal means includes a generally ramped signal.

6. A control system for guiding a vehicle over a floor along a long, narrow stripe of reflective material applied to the floor to define a desired path for the vehicle to travel, comprising:

means for generating light and directing said light toward the reflective material;

a generally linear array of light sensors mountable on the vehicle generally transverse to the strip of reflective material, each sensor having a field of view and generating an output signal generally proportional to the portion of the sensor'"'"'s field of view occupied by the reflective material;

reference signal means for generating a reference signal with an amplitude generally unidirectionally and progressively changing over a preselected time period;

means for comparing each of said sensor output signals to said reference signal on a plurality of sampling occasions during said preselected time period, and on each sampling occasion generating a binary output having binary states for each of said sensors, said binary output in one binary state indicating if the amplitude of said sensor output signal is above said reference signal and in the other binary state indicating if the amplitude of said sensor output signal is below said reference signal;

position value means for combining said sensor binary outputs generated for each sampling occasion and deriving a position indicating value therefrom indicative of the lateral position of said sensor array relative to the reflective material at the time of said sampling occasion based upon the changing threshold provided by said reference signal; and

means for combining all said position indicating values for said one preselected time period and generating a vehicle command therefrom comprising a vehicle lateral directional command to control the direction of lateral movement of the vehicle as it travels along the path.

7. The control system of claim 6 wherein said position value means combines said sensor binary outputs generated for each sampling occasion in a predetermined order to generate a byte, with each said byte comprising one of said corresponding position indicating values.

8. The control system of claim 6 wherein said vehicle command for said one preselected time period further comprises a vehicle lateral displacement command to control the amount of lateral movement of the vehicle as it travels along the path.

9. The control system of claim 8 wherein said position value means includes:

means for converting said binary outputs for each sampling occasion generated during said one preselected time period into a corresponding table location value;

a look-up table storing a plurality of said position indicating values, each position indicating value being stored at a table location corresponding to one of said table location values, each said position indicating value comprising a vehicle lateral directional command component indicative of the direction of lateral movement of the vehicle required to travel along the path and a vehicle lateral displacement command component indicative of the amount of lateral movement of the vehicle required to travel along the path, said vehicle direction and displacement command components being based upon the lateral position of said sensor array relative to said reflective material at the time of said sampling occasion corresponding to said table location value as measured using the changing threshold provided by said reference signal; and

look-up means for looking up ones of said position indicating values stored in said look-up table at said table locations corresponding to said table location values.

10. The control system of claim 9 wherein said look-up table includes a first table storing a first plurality of said position indicating values, each comprising one of said vehicle directional and displacement command components directing the vehicle to follow the left edge of the reflective material, and a second table storing a second plurality of said position indicating values, each comprising one of each of said vehicle directional and displacement command components directing the vehicle to follow the right edge of the reflective material.

11. The control system of claim 10, further including:

means for selecting whether the vehicle is to follow the left or right edge of the reflective material in response to instruction to the control system; and

means for causing said look-up means to look up in the one of said first or second tables corresponding to the left or right edge selected by said selecting means for the vehicle to follow, each of said first and second tables including corresponding ones of said first or second plurality of said position indicating values stored at said table locations corresponding to said table location values.

12. The control system of claim 6 wherein said reference signal means includes a generally ramped signal.

13. The control system of claim 6 wherein said reference signal is a stair-step signal, and said reference signal means includes clock means for generating a clock signal, counter means for counting said clock signals up to a predetermined number during said preselected time period and generating count indicating signals, and summing means for summing said count indicating signals and therefrom generating said stair-step signal.

14. A control system for guiding a vehicle over a floor, comprising:

a long, narrow stripe of retroreflective material adhesively applied to the floor to define a desired path for the vehicle to travel along;

means for generating light and directing said light toward said retroreflective material;

a generally linear array of a plurality of light sensors mountable on the vehicle generally transverse to said stripe of retroreflective material, each sensor having a field of view and generating an output signal generally proportional to the portion of the sensors'"'"'s field of view occupied by said retroreflective material;

means for repetitively generating a reference signal with an amplitude changing over a preselected time period;

means for comparing each of said sensor output signals to said reference signal during said preselected time period, and generating a binary output signal having binary states for each of said sensors, said binary output signal in one binary state indicating if the amplitude of said sensor output signal is above said reference signal and in the other binary state indicating if the amplitude of said sensor output signal is below said reference signal;

means for sampling the value of each of said sensor binary output signals on a plurality of sampling occasions during said preselected time period and combining said sampled values of said sampled sensor binary output signals for each sampling occasion in a predetermined order to generate a byte, with each byte indicative of the lateral position of said sensor array relative to said retroreflective material at the time of said sampling occasion based upon the changing threshold provided by said reference signal; and

converting means for converting said bytes generated for said sampling occasions during said preselected time period into a vehicle lateral directional command therefrom to control the direction of lateral movement of the vehicle as it travels along said path.

15. The control system of claim 14 wherein said converting means comprises:

means for deriving a vehicle position indicating value corresponding to each of said bytes generated during said preselected time period; and

means for mathematically summing the values of said position indicating values derived from said bytes for said sampling occasions during said one preselected time period and generating a summed value for said one preselected time period, said summed value for said one preselected time period comprising said vehicle lateral directional command, whereby said vehicle lateral directional command is based upon the composite lateral directional position of said sensor array relative to said retroreflective material determined at each of said sampling occasions during said one preselected time period as measured using the changing threshold provided by said reference signal, and whereby the control system increases its resolution by effectively interpolating the position of the retroreflective material between pairs of said sensors.

16. The control system of claim 15 wherein said summed value for said one preselected time period further comprises a vehicle lateral displacement command to control the amount of lateral movement of the vehicle as it travels along said path, whereby said vehicle lateral displacement command is based upon the composite lateral displacement of said sensor array relative to said retroreflective material determined at each of said sampling occasions during said open preselected time period as measured using the changing threshold provided by said reference signal.

17. The control system of claim 15 wherein each of said bytes generated during said one preselected time period corresponds to a table location value, and said means for deriving said vehicle position indicating values further includes:

a look-up table storing a plurality of said position indicating values, each position indicating value being stored at a table location corresponding to one of said table location values, each said position indicating value comprising a vehicle lateral directional command component indicative of the direction of lateral movement of the vehicle required to travel along the path and a vehicle lateral displacement command component indicative of the amount of lateral movement of the vehicle required to travel along the path, said vehicle directional and displacement command components being based upon the lateral position of said sensor array relative to said retroreflective material at the time of said sampling occasion corresponding to each of said bytes as measuring using the changing threshold provided by said reference signal; and

look-up means for looking up ones of said position indicating values stored in said look-up table at said table locations corresponding to said table location values.

18. The control system of claim 17 wherein said look-up table includes a first table storing a first plurality of said position indicating values, each comprising one of said vehicle directional and displacement command components directing the vehicle to follow the left edge of the reflective material, and a second table storing a second plurality of said position indicating values, each comprising one of each of said vehicle directional and displacement command components directing the vehicle to follow the right edge of the reflective material.

19. A method for guiding a vehicle along a long, narrow strip of reflective material defining a desired path for the vehicle to travel, comprising:

generating light and directing the light toward the reflective material;

providing a generally linear array of light sensors mountable on the vehicle generally transverse to the stripe of reflective material, with each sensor having a field of view;

generating an output signal generally proportional to the portion of the sensor'"'"'s field of view occupied by the reflective material;

generating a reference signal with an amplitude generally unidirectionally and progressively changing over a preselected time period;

comparing each of said sensor output signals to said reference signal during said preselected time period;

generating a binary output signal having binary states for each of said sensors, with said binary output signal in one binary state being indicative of whether the amplitude of said sensor output signal is above said reference signals and in the other binary state being indicative of whether the amplitude of said sensor output signal is below said reference signal;

sampling the value of each of said sensor binary output signals on a plurality of sampling occasions during said preselected time period;

combining said sampled values of said sensor binary output signals for each sampling occasion in a predetermined order to generate a byte, with each said byte being indicative of a lateral position of said sensor array relative to the reflective material at the time of said sampling occasion based upon the changing threshold provided by said reference signal and with each said byte corresponding to a table location value;

providing a look-up table storing a plurality of position indicating values, each position indicating value being stored at a table location corresponding to one of said table location values, with each said position indicating value comprising a vehicle lateral directional command component indicative of the direction of lateral movement of the vehicle and a vehicle lateral displacement command component indicative of the amount of lateral movement of the vehicle required to travel along the path;

looking up ones of said position indicating values stored in said look-up table at said table locations corresponding to said table location values corresponding to said bytes generated for said one preselected time period; and

mathematically summing all of said position indicating values for said one preselected time period and generating a summed vehicle command comprising a vehicle lateral directional command and a vehicle lateral displacement command to control the direction of lateral movement and the amount of lateral movement of the vehicle as the vehicle moves along the path.

20. The method of claim 19, further including a first table storing a first plurality of said position indicating values, each comprising one of said vehicle directional and displacement command components directing the vehicle to follow the left edge of the reflective material, and a second table storing a second plurality of said position indicating values, each comprising one of each of said vehicle directional and displacement command components directing the vehicle to follow the right edge of the reflective material;

and

providing means for selecting whether the vehicle is to travel the left or right edge of the reflective material in response to instruction to the control system.

21. A control system for guiding a vehicle along a long, narrow stripe of reflective material defining a desired path for the vehicle to travel, comprising:

a light source generating light and directing the light toward the reflective material;

a generally linear array of light sensors mountable on the vehicle generally transverse to the strip of reflective material, each sensor having a field of view and generating an output signal generally proportional to the portion of the sensor'"'"'s field of view occupied by the reflective material;

a reference signal generator generating a reference signal with an amplitude generally unidirectionally and progressively changing over a preselected time period;

a comparator comparing each of said sensor output signals to said reference signal on a plurality of sampling occasions during said preselected time period, and on each sampling occasion generating a binary output signal having binary states for each of said sensors, said binary output signal in one binary state indicating if the amplitude of said sensor output signal is above said reference signal and in the other binary state indicating if the amplitude of said sensor output signal is below said reference signal;

a byte generator sampling the value of each of said sensor binary output signals on a plurality of sampling occasions during said preselected time period and combining said sampled values of said sensor binary output signals for each sampling occasion in a predetermined order to generate a byte, with each said byte being indicative of the lateral position of said sensor array relative to the reflective material at the time of said sampling occasion based upon the changing threshold provided by said reference signal and with each said byte corresponding to a table location values;

a look-up table storing a plurality of position indicating values, each position indicating value being stored at a table location corresponding to one of said table location values, with each said position indicating value comprising a vehicle lateral directional command component indicative of the direction of lateral movement of the vehicle required to travel along the path and a vehicle lateral displacement command component indicative of the amount of lateral movement of the vehicle required to travel along the path, said vehicle directional and displacement command components being based upon the lateral position of said sensor array relative to said reflective material at the time of said sampling occasion corresponding to each of said bytes as measured using the changing threshold provided by said reference signal;

a look-up device which looks up ones of said position indicating values stored in said look-up table at said table locations corresponding to said table location values corresponding to said bytes generated for said one preselected time period; and

a summer mathematically summing all said position indicating values for said one preselected time period and generating a final vehicle command comprising a vehicle lateral directional command and a vehicle lateral displacement command to control the direction and amount of lateral movement of the vehicle as the it travels along the path.

22. The control system of claim 21 wherein said look-up table includes a first table storing a first plurality of said position indicating values, each comprising one of said vehicle directional and displacement command components directing the vehicle to follow the left edge of the reflective material, and a second table storing a second plurality of said position indicating values, each comprising one of each of said vehicle directional and displacement command components directing the vehicle to follow the right edge of the reflective material.