robotic sensors

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• What is a robotic sensor?

Agenda

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• What is a robotic sensor?• How do they work?

Agenda

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• What is a robotic sensor?• How do they work?• What can they be used for?

Agenda

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• What is a robotic sensor?• How do they work?• What can they be used for?• Practical examples, including code &

demonstration

Agenda

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• Detects information about the physical world

What is a Robotic Sensor?

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• Detects information about the physical world?

• Converts this information into an electrical signal suitable for the robot’s computer controller


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Simple Switch for sensing physical contact:

Function: Consists of two electrical contacts – they make or break a connection when the switch is activated

Examples of Robotic Sensors

(click for image)

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Simple Switch for sensing physical contact:

Function: Consists of two electrical contacts – they make or break a connection when the switch is activated

Where Used: • joystick trigger• limit switch on robot arm• bumper switch on robot• detect presence of a ball in a hopper…


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How to Connect: • connect Common (COM) lead on switch to GND pin on Robot

Controller digital input• connect normally open (NO) lead on switch to SIG pin on Robot

Controller digital input

Simple Switch

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How to Program:

• Define the desired digital I/O pin as input, if this is not already done in the default code:

– e.g.: digital_io_02 = INPUT;

• Use the switch input as follows:

If (rc_dig_in02 = 0){

pwm01 = 127 /* stops motor if switch pushed*/}

Simple Switch

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Optical Sensor for physical presence: interrupted & reflected type are available

Function: Consists of light source (LED) and light detector (photocell), can sense by interruption or reflection of beam


(click for image)

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Where Used: • Interruption – detects presence of object inside optical gap,

could be a flange on a robotic arm, a tooth on a sprocket…


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Where Used: • Interruption – detects presence of object inside optical gap,

could be a flange on a robotic arm, a tooth on a sprocket…• Reflective – could count light and dark stripes on robot’s

drive wheel to measure distance traveled


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Optical Sensor

• How to Program:

• Define the desired digital I/O pin as input, if this is not already done in the default code:– e.g.: digital_io_02 = INPUT;

• Read the sensor input as follows:– If (rc_dig_in02 = 0)

{/* increment wheel count if sensor goes from 1 to

0*/}

•

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Rotary or shaft encoder for measuring shaft angle

Function: Consists of magnetic reed switches, or light source (LED) and light detector (photocell) with an encoder wheel


(click for image)

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Function: Consists of magnetic reed switches, or light source (LED) and light detector (photocell) with an encoder wheel

Where Used: • On a drive axle to measure speed and distance• On an arm to measure position• On a turret to measure angle


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How to Program: Usually consists of multiple digital outputs – connect these to

digital inputs on Robot Controller, and read these to determine when they change.

• Read the sensor input as follows:– If (rc_dig_in02 = 1 && rc_dig_in03 = 1 && rc_dig_in04 = 1)

{/* shaft is at 220º to 270 º angle*/

}


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Ultrasonic transducer for measuring distance

Function: Consists of an ultrasonic transmitter and receiver. Circuitry

Where Used: • On the front or side of a robot to measure distance to a

wall


(click for image)

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• Examples of sensors include:– Simple Switch for physical contact: joystick trigger, limit switch– Light beam for physical presence: interrupted & reflected– Rotary or Shaft Encoder for measuring rotary angle– Ultrasonic for measuring distance– Infra-red for measuring distance


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• Examples of sensors include:– Simple Switch for physical contact: joystick trigger, limit switch– Light beam for physical presence: interrupted & reflected– Rotary or Shaft Encoder for measuring rotary angle– Ultrasonic for measuring distance– Infra-red for measuring distance– Microphone for listening


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• Examples of sensors include:– Simple Switch for physical contact: joystick trigger, limit switch– Light beam for physical presence: interrupted & reflected– Rotary or Shaft Encoder for measuring rotary angle– Ultrasonic for measuring distance– Infra-red for measuring distance– Microphone for listening– Camera for seeing


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• Examples of sensors include:– Simple Switch for physical contact: joystick trigger, limit switch– Light beam for physical presence: interrupted & reflected– Rotary or Shaft Encoder for measuring rotary angle– Ultrasonic for measuring distance– Infra-red for measuring distance– Microphone for listening– Camera for seeing– Accelerometer for measuring acceleration & position– …….


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• Measuring Distance using Sharp GP2Y0A02YK – Measures distance from 20 cm to

150 cm

Specific Example – IR rangefinder

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150 cm– Provides analog output: 0 to 5 V


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150 cm– Provides analog output: 0 to 5 V– Can be connected directly to

Robot Controller’s analog input


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Robot Controller’s analog input– Has a spot beam, for accurate

aiming


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aiming– Is immune to color or reflectivity

of the environment


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aiming– Is immune to color or reflectivity

of the environment– Costs ~ $12.00


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• Available from acroname, digikey, sparkfun and others• Connect as follows:

Sharp GP2Y0A02YK rangefinder

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• Read voltage using analog input command on Robot Controller:

ir_sensor = Get_Analog_Value(rc_ana_in16);

• This value will range between ~ 10 (at 150 cm) and ~ 580 (~ 20 cm)

Programming for the Sharp GP2Y0A02YK

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if (ir_sensor > lower_limit && ir_sensor < upper_limit )

{

pwm01 = 127; /* set servo to middle position */

}

Sample code: sets a servo to a different position depending on sensor distance

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{


}

Else /* not in middle range */

{ if (ir_sensor < lower_limit) /* check sensor for far away*/

{

pwm01 = 0; /* set servo to far position */

}


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{


}

Else /* not in middle range */

{ if (ir_sensor < lower_limit) /* check sensor for far away*/

{

pwm01 = 0; /* set servo to far position */

}

Else

{

pwm01 = 253; /* set servo to near position */

}

}


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• You can use the sensor output to control the speed of the left & right drive wheels so your robot will keep a specified distance from a wall.

IR Rangefinder

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• Use a second IR rangefinder to stop the robot or turn it when it approaches a wall in front of it.

IR Rangefinder

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• Use a second IR rangefinder to stop the robot or turn it when it approaches a wall in front of it.

• The IR rangefinder is a very useful and easy-to-use sensor, and is just one of many sensors you can use on your robot.

IR Rangefinder

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Thank you.

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END

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SwitchClick anywhere to return

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Click anywhere to return

Optical Interrupter Optical Reflector

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Rotary Encoder Encoder Disc, read by optical sensors inside decoder


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Ultrasonic Rangefinder


robotic sensors

Education

switch input

examples of sensors

physical presence

robotic arm

sensor input

limit switch light beam

optical sensor

physical contact