TRIWG Review June 1998 - Computer Action Team

TRIWG Review June 1998 - Computer Action Team

IR sensitive - sense heat differences and construct images, night vision application Infra Red sensors emitter/receiver pairs Active Sensors Used in Lynxmotion, Robix and Lego robots

Modulation Modulation // Demodulation Demodulation of of Light Light and and Infra-Red Infra-Red Sensors Sensors Modulation and Demodulation of Light

Ambient light is a problem because it interferes with the emitted light from a light sensor. One way to get around this problem is to emit modulated light. The modulated light rapidly turns the emitter on and off. Modulated signa much easier and more reliably detected by a demodulator Demodulator is tuned to the particular frequency of the modulated light. Modulation and Demodulation of Light Not surprisingly, a detector needs to sense several on-flashes in a row in order to detect a signal.

It means, to detect signal frequency. This is important when you write the demodulator code. The idea of modulated IR light is commonly used; in household remote controls. Modulated light sensors are generally more reliable than basic light sensors. They can be used for the same purposes: detecting the presence of an object measuring the distance to a nearby object (clever

electronics required, see Martins textbook) Infra Red (IR) Sensors Infra red sensors are a type of light sensors They function in the infra red part of the frequency spectrum. IR sensors are active sensors They consist of: an emitter a receiver. IR sensors are used in the same ways as the visible light sensors are: as break-beams, as reflectance sensors.

Infra Red (IR) Sensors IR is preferable to visible light in robotics (and other) applications. This is because it suffers a bit less from ambient interference, because it can be easily modulated, because it is not visible. Sharp Infra Red Detector Sharp IR Detector The Sharp GP1U52X sensor detects infrared light that is modulated (i.e., blinking on and off)

at 40,000 Hz. It has an active low digital output: meaning that when it detects the infrared light, its output is zero volts. The metal case of the sensor must be wired to circuit ground, as indicated in the diagram. This makes the metal case act as a Faraday cage, protecting the sensor from electromagnetic noise. Sharp IR Detector It is a digital sensor because it detects infrared light modulated at 40kHz.

Not analog! Inside the tin can, there is a IR detector, amplifier, and a demodulator. The sensor returns a HIGH when there is no 40kHz light, and is LOW when it sees the 40kHz light. Sharp IR sensor assembly Sharp IR Detector You can use the IC command ir counts(port) to count the number of successive detected periods of the modulated frequency. A count larger than 10 indicates a detection. You may need to play around with what values of the counts are needed

for detection. These sensors can only be used in digital ports 4-7. Elimination of the effect of the stray IR light There is a lot of infrared light that is ambient in the air. Some components of this light are at 40kHz, and straight output from the sensor would look very glitchy. The sun produces a lot of IR light, and in the sun, the sensor output bounces all over the place. To eliminate the effect of the stray IR light, the IR emitters are modulated at 100 or 125 Hz and the output of the IR Detectors is demodulated to look for these frequencies.

(see section A.7 for more information on the IR transmission) The 40kHz frequency is known as the carrier frequency, and the other frequency is the modulated frequency. IR Photo Transistor The bundle-of-wires" phototransistors are much more predictable.

Phototransistor body and connector They should be wired with a resistor of 100k to 300k (we recommend 220k). They barely respond at all to visible frequencies of light. They respond particularly

well to the LEDs with which they are bundled, as well as to the grey IR LEDs. Both LEDs are highly directional, and you should be able to get good breakbeam results up to 5 or 6 cm apart (2 inches). This might prove especially useful in ball-ring mechanisms, for example. Note that both LEDs and phototransistors are just the right size to fit in LEGO axle-holes!

Reflective Optosensors If we use a light bulb in combination with a photocell, we can make a break-beam sensor. This idea is the underlying principle in reflective optosensors: the sensor consists of an emitter and a detector. Reflective Optosensors Depending of the arrangement of those two relative to each other, we can get two types of sensors: reflectance sensors the emitter and the detector are next to each

other, separated by a barrier; objects are detected when the light is reflected off them and back into the detector break-beam sensors the emitter and the detector face each other; objects are detected if they interrupt the beam of light between the emitter and the detector IR Reflective Optosensors Transmitter LED: only infrared light by filtering out visible light Light detector (receiver) (photodiode

or phototransistor) Light from emitter LED bounces off of an external object and is reflected into the detector Quantity of light is reported by the sensor Depending on the reflectivity of the surface, more or less of the transmitted light is reflected into the detector This is an analog sensor - connects to board analog ports Sensors Light-emitting component aimed at a light-detecting component When opaque object comes

between emitter and detector, the beam of light is occluded, and the output of the detector changes Discrete infrared LED Any pair of compatible emitterdetector devices may be used: 1. Incandescent flashlight bulbs and photocells 2. Red LEDs and visible-light-sensitive phototransistors 3. Infrared emitters and detectors phototransistor various commercial

break-beam optosensors Reflective Optosensors The emitter is usually made out of a lightemitting diode (an LED). The detector is usually a photodiode/phototransistor. Note that these are not the same technology as resistive photocells. Resistive photocells are nice and simple, but their resistive properties make them slow. Photodiodes and photo-transistors are much faster and therefore the preferred type of technology. Light Reflectivity. What can you do with this simple idea of

light reflectivity? Quite a lot of useful things: object presence detection In Lego object distance detection surface feature detection (finding/following markers/tape) wall/boundary tracking rotational shaft encoding (using encoder wheels w/ ridges or black & white color) bar code decoding Light Reflectivity. Light reflectivity depends on the color (and other properties) of a surface. A light surface will reflect light better than a

dark one, and a black surface may not reflect it at all, thus appearing invisible to a light sensor. Darker objects harder (less reliable) to detect . In the case of object distance, lighter objects that are farther away will seem closer than darker objects that are not as far away. Light Reflectivity. This gives you an idea of how the physical world is partiallyobservable; even though we have useful sensors, we do not have complete and completely accurate information.

Active Light Sensing The agent illuminates what is being sensed and uses the reflected light Can be used for a number of tasks collision avoidance/proximity detection following (mail delivery) We will discuss line following Line Detecting and Following Circuit Passive Light Sensing Light is received from the environment

directly Used to, locate, move towards, or avoid We will discuss a single cell eye The Cyclops Circuit Cross connected single eyes Single Photo-resistor per side Controls a differentially steered vehicle e.g. The Solenodon IV Partial Circuit

What are the applications of Reflective Optosensors? 1. Object detection. Reflectance sensors may be used to measure the presence of an object in the sensors field of view. In addition to simply detecting the presence of the object, the data from a reflectance sensor may be used to indicate the objects distance from the sensor. Disadvantage: These reading are dependent on the reflectivity of the object, among other thingsa highly reflective object that is farther away may yield a signal as strong as a less reflective object that is closer. 2. Surface feature detection. Reflective optosensors are great for detecting features painted, taped, or otherwise marked onto the floor. Line-following using a reflective sensor is a typical robot activity.

What are the applications of Reflective Optosensors? 3. Wall tracking. Related the object detection category, this application treats the wall as a continuous obstacle and uses the reflective sensor to indicate distance from the wall. 4. Rotational shaft encoding. Using a pie-shaped encoder wheel, the reflectance sensor can measure the rotation of a shaft (angular position and velocity). 5. Barcode decoding. Reflectance sensors can be used to decode information from barcode markers placed in the robots environment.

Interfacing Reflective Optosensors Two components of the sensor, the emitter and detector, have logically separate circuits, though they are wired to the same connector plug Detector Q1, shown as a phototransistor, is wired between ground and the sensor signal linejust like a photocell The emitter LED (LED1), is wired to the Handy Boards +5v power supply through R1, the current-limiting resistor R1s value can vary 220-47, depending on how much brightness is desired

from the emitter LED Reflectance Sensor Interface Diagram How do you choose, Photocells or Phototransistors? Properties of Photocells: easy to use - electrically they are resistors, their response time is slow compared to the photodiode or phototransistors semiconductor junction. photocells are suitable for: detecting levels of ambient light, or acting as break-beam sensors in low frequency applications (e.g., detecting when an object is between two fingers of a robot gripper). Properties of Photodiodes and Phototransistors: where we need a rapid response time:

shaft encoding, more sensitive to small levels of light, which allows the illumination source to be a simple LED element. Interfacing Phototransistors Current creates a voltage drop in the 47K pullup resistor on HB Light-sensitive current source: the more light reaching the phototransistor, the more current passes through it This voltage drop is reflected in a smaller voltage on the Vsens sensor signal line, which has a level that is equal to 5 volts minus the 47K resistors voltage drop Smaller values than 47K may be required to obtain good performance from the circuit

If transistor can typically generate currents >= 0.1 mA, then voltage drop across the pull-up resistor will be so high as to reduce Vsens to zero Solution is to wire a smaller pull-up resistor with the sensor itself The current, i, flowing through the Q1 phototransistor is indicated by the dashed line. Quality Technologies QRD1114 IR Optosensor LED emitter and detector phototransistor or photodiode are matched.

Emitter LED connects through 330K resistor to +5v supply (constantly on) This means that peak sensitivity of the detector is at same wavelength of emissions of the emitter You should use infrared detector card to test IR light output Wiring Detector transistor pulled high with HB internal 47K resistor May have trouble figuring out which element is transistor and which is detector Length of leads: longer +, shorter -

Detector connects to sensor signal line BreakBeam Sensors 5.5.9 Breakbeam Sensors Figure 5.9: Reflectance Sensor Break-beam Sensors We already talked about the idea of breakbeam sensors. In general, any pair of compatible emitterdetector devices can be used to produce such a sensors: 1. an incandescent flashlight bulb and a photocell

2. red LEDs and visible-light-sensitive photo-transistors 3. infra-red IR emitters and detectors Figure 5.10: Breakbeam Sensor using discrete components . Breakbeam sensors Breakbeam sensors are another form of light sensors. Instead of looking for reflected light, the photosensor

looks for direct light as shown in Figure 5.10. The sensor is useful in detecting opaque objects that prevent the light beam from passing through. This can be useful in detecting block between gripper, or when block passes through a passageway. The sensor does not need to detect the block very quickly so the phototransistor can be plugged into the analog port. Figure 5.11: Breakbeam Assembly Figure 5.12: Shaft encoding using a LEGO pulley Wheel Breakbeam sensors

The breakbeam sensors can also be used for counting holes or slots in a disk as it rotates (see Figure 5.12), allowing distance traveled to be measured. Since this requires a very fast sampling, the sampling needs to be done at the assembly language level. We have implemented shaft-encoder routines to do the fast sampling. But in order to use these routines the sensors should be plugged into the lower two digital ports if the rate at which the holes or slots go by is very high. Before you use the analog sensors in the digital switch you must make sure that there is a full swing in the analog reading from when the light goes through to when the light is blocked. Motorola MOC70V1

Infrared Break-Beam Optosensor For sensing objects between larger gaps, use discrete emitters and detectors Interface to HB the same as for the reflective optosensors Emitter LED powered from HB +5v supply through dropping resistor Detector phototransistor connected between sensor signal line and ground Polarity is not indicated by length of device leads; look for + marking Consider many robotic applications for

break-beam sensing e.g., detecting something between fingers of a robotic gripper Ambient light. Another source of noise in light sensors is ambient light. The best thing to do is subtract the ambient light level out of the sensor reading, in order to detect the actual change in the reflected light, not the ambient light. How is that done? By taking two (or more, for higher accuracy) readings of the detector, one with the emitter on, and one with it off, and subtracting the two values from each other. The result is the ambient light level, which can then be subtracted from future readings.

This process is called sensor calibration. Of course, remember that ambient light levels can change, so the sensors may need to be calibrated repeatedly. What kind of Processing we need for Infrared Sensors? 1. Correct for ambient light 2. Calibrate light levels for dark and light surfaces 3. Process the data to avoid spurious readings 4. Process the data

adapting to changing conditions 1. Correcting Reflective Optosensors for Ambient Light Question: How can a robot tell the difference between: a stronger reflection an increase in light in the robots environment? Answer: switch a reflectance sensors emitter light source on and off under software control Take two light level readings, one with the emitter on, and one with the emitter off, then subtract away the ambient light levels

Wiring an LED to bit 2 of Port D (Serial Peripheral Interface) Pin int active_read(int port) { int dark, light; /* local variables */ dark= analog(port); /* reading with light off */ bit_set(0x1009, 0b00000100); /* turn light on */ light= analog(port); /* reading with light on */ bit_clear(0x1009, 0b00000100); /* turn light off */ return dark - light; Subtract }

ambient light from each IR reading Correcting for Ambient Light Need to differentiate between transmitted light and normal ambient light Can do so by using photosensor to read ambient light levels with transmitter off Can either use external photosensor Or use packaged photosensor if wired correctly Subtract ambient light from each IR reading Alternating ambient and IR readings

Info about HB digital electronics: Typical LED draws 5-20 mA Typical processor digital output can supply 20-25 mA So, a 68HC11 pin can drive 1-5 LEDs 2. Sensor Calibration for dark and light surfaces Robot is physically positioned over the line and floor and a threshold setpoint is captured Declare and use calibration routine setpoint variables

are persistent int LINE_SETPOINT= 100; int FLOOR_SETPOINT= 100; void calibrate() { int new; while (!start_button()) { new= line_sensor(); printf("Line: old=%d new=%d\n", LINE_SETPOINT, new); msleep(50L); } LINE_SETPOINT= new; /* accept new value */ beep(); while (start_button()); /* debounce button press */

while (!start_button()) { new= line_sensor(); printf("Floor: old=%d new=%d\n", FLOOR_SETPOINT, new); msleep(50L); } FLOOR_SETPOINT= new; /* accept new value */ beep(); while (start_button()); Huge*/improvement /* debounce button press } over fixed and hard- NOTE DEBOUNCING BUTTON PRESSES

coded calibration methods Proximity Sensing with Infrared Pair Proximity sensing: reflect IR off nearby object detect returned light emitter and detector point in same direction Modulated light By rapidly turning on and off, the source of light can be easily picked up from varying background illumination

Proximity Sensing with Infrared Pair Modulated light By rapidly turning on and off, the source of light can be easily picked up from varying background illumination Proximity Sensing with Infrared With modulated light detector, object is either present or absent Modulated light is less susceptible to environment variables but non-modulated light magnitude sensing/thresholding works also

Could try to determine objects distance as well but, Re-Visiting IR Calibration IR is very sensitive to ambient lighting, different color obstacles, varying distances, differing lighting conditions Combining Light and IR to Infer Distance IR = f(color, reflectance, ambient light, distance) Dont have a sensor that measures color Distance is what we want So what we do? 1. We condition based on ambient light 2. We hope that all the obstacles are the same color/

reflectance Closed-loop Control Obstacle avoidance and tracking Drive parallel to wall Using a Proximity Sensor to Measure Distance to a Wall Feedback from proximity sensors (e.g. bump, IR, sonar) Feedback loop, continuous monitoring and correction of motors -- adjusting distance

to wall to maintain goal distance Separate Sensor State Processing from Control Functions might each make use of other sensors and functions need to decide how to implement each Use Proximity Sensor to Select One of Three States Sensor used to select one of three states Obstacle Avoidance and

Tracking Using IR Have continuously running task update IR state: Left, right, both, neither If one obstacle detected then use closed-loop control to keep it away from robot If two obstacles detected then Either assume you cant pass and treat like bump Or try to pass in-between with

closed-loop control Depends on how you mounted/shielded your sensors, how you set your thresholds, and any ability to differentiate distances Use of Infrared Ground Sensor Concluding on Local Proximity Sensing using IR Infrared LEDs cheap, active sensing usually low resolution - normally used for presence/absence of obstacles rather than

ranging operate over small range Shaft Encoding Our Wheel Encoders Optical encoder to measure wheel rotation of each drive wheel Slotted disk attached to wheel or motor shaft Break-beam IR counts number of slots that pass in given time (ports 7,8 )

Enable_encode, disable_encoder, read_encoder (number of on/offs since last reset), reset_encoder Max 32,767 counts (16 bit) Encoder library must be loaded Basics of Shaft Encoders A shaft encoder is a device that measures the position of a shaft. There are two types of shaft encoders. One is incremental shaft encoder which produces a pulse train of a certain frequency depending on the rotational speed of its shaft. The other one is the absolute shaft

encoder which measures the absolute position of its shaft. Incremental shaft encoders. A Shaft 64 Segments Photo Interrupter Pulse Train Shaft Encoding Use Break-Beam Sensors Shaft encoder measures the

angular rotation of an axle, reporting position and/or velocity information Example: speedometer, which reports how fast the wheels are turning; odometer, which keeps track of the number of total rotations Single-Disk Shaft Encoder A perforated disk is mounted on the shaft and placed between the emitterdetector pair. As the shaft rotates, the holes in the disk chop the light beam. Hardware and software connected to the detector keeps track of these light pulses, thereby

monitoring the rotation of the shaft. Shaft Encoding Shaft encoders measure the angular rotation of an axle providing position and/or velocity info. A speedometer measures how fast the wheels of a vehicle are turning, An odometer measures the number of rotations of the wheels. In order to detect a complete or partial rotation, we have to somehow mark the turning element. This is usually done by attaching a round disk to the shaft, and cutting notches into it.

Shaft Encoding A light emitter and detector are placed on each side of the disk, so that: as the notch passes between them, the light passes, and is detected; where there is no notch in the disk, no light passes. If there is only one notch in the disk, then a rotation is detected as it happens. This is not a very good idea, since it allows only a low level of resolution for measuring speed: the smallest unit that can be measured is a full rotation. Shaft Encoding Besides, some rotations might be missed due to noise.

Usually, many notches are cut into the disk, and the light hits impacting the detector are counted. (You can see that it is important to have a fast sensor here, if the shaft turns very quickly.) An alternative to cutting notches in the disk is to: paint the disk with black (absorbing, non-reflecting) and white (highly reflecting) wedges, and measure the reflectance. In this case, the emitter and the detector are on the same side of the disk. Shaft Encoding In either case, the output of the sensor is going

to be a wave function of the light intensity. This can then be processed to produce the speed, by counting the peaks of the waves. Note that shaft encoding measures both position and rotational velocity, by subtracting the difference in the position readings after each time interval. Velocity, on the other hand, tells us how fast a robot is moving, or if it is moving at all. Shaft Encoding There are multiple ways to use velocity: measure the speed of a driven (active) wheel use a passive wheel that is dragged by the robot (measure forward progress)

We can combine the position and velocity information to do more sophisticated things: move in a straight line rotate by an exact amount Note, however, that doing such things is quite difficult, because: wheels tend to slip (effector noise/error) and slide and there is usually some slop and backlash in the gearing mechanism. Shaft encoders can provide feedback to correct the

errors, but having some error is unavoidable. Quadrature Shaft Encoding So far, we've talked about detecting position and velocity, but did not talk about direction of rotation. Suppose the wheel suddenly changes the direction of rotation; it would be useful for the robot to detect that. An example of a common system that needs to measure position, velocity, and direction is a computer mouse. Without a measure of direction, a mouse is pretty useless. How is direction of rotation measured?

Quadrature Shaft Encoding Quadrature shaft encoding is an elaboration of the basic break-beam idea; instead of using only one sensor, two sensors are needed. The encoders are aligned so that their two data streams coming from the detector are one quarter cycle (90degrees) out of phase, thus the name "quadrature". By comparing the output of the two encoders at each time step with the output of the previous time step, we can tell if there is a direction change. When the two are sampled at each time step, only one of them will change its state (i.e., go from on to off) at a time, because they are out of phase.

Quadrature Shaft Encoding Which one does, it determines which direction the shaft is rotating. Whenever a shaft is moving in one direction, a counter is incremented, and when it turns in the opposite direction, the counter is decremented, thus keeping track of the overall position. Other uses of quadrature shaft encoding are in: robot arms with complex joints (such as rotary/ball joints; think of your knee or shoulder), Cartesian robots (and large printers) where an arm/rack moves back and forth along an axis/gear. Shaft Encoding

Data from shaft encoder built from MOV70V1 breakbeam sensor and pulley wheel: The sensor data graph is a nearly ideal square wave. Using the standard HB analog input, which reports a sensor reading between 0 and 255, the sensors output varies from a low of about 9 (about 0.18 volts) to a high of about 250 (4.9 volts) with a sharp edge between the transitions. Other break-beam sensors yield a time graph that looks more like a sine wave. This assembly uses the Motorola breakbeam sensor with the medium pulley wheel as a photo-interrupter. After determining a position of the breakbeam sensor that yielded good break and make transitions, the sensor was hotglued into position along the LEGO beam.

Shaft Encoding Counting Encoder Clicks To make sense of data from a shaft encoder, install a routine that repeatedly checks the sensor value. If the encoder wheel turns faster than the routine checks the sensor state, it will start missing transitions and lose track of the shafts rotation Solution: check midrange point Variables for algorithm: encoder_state - Keeps track of last encoder reading:1 if high (above 128), 0 if low (below 128) encoder_counter - Keeps running total of encoder clicks

Shaft Encoding Driver Software Machine language routine loaded into ICs underlying layer of direct 68HC11 code, with user interface - IC binary (ICB) files installed in interrupt structure of 68HC11 Monitors shaft encoder values and calculates encoder steps and velocity needs quickly and at regular intervals HBs software libraries include set of routines for supporting shaft encoders for both positioncounting and velocity measurement. For each analog input on HB, a pair of shaft encoder routines is provided. For each pair, there is a high-speed version and a low-speed version. High speed version checks for transitions on the encoder sensor 1000 Hz Low speed version checks encoder at 250 Hz (less of a processing load on the system) Both versions calculate the velocity (position difference) measurement at about 16 Hz Once loaded into IC, the encoder routines are automatically active; no additional commands are needed to turn them on. Each encoder0_counts variable (running total of transitions on encoder sensor) will automatically increment every time it senses a transition on its corresponding encoder sensor

The encoder0_velocity value (velocity measurement) is continuously updated Library Drivers to do the Counting Machine language routine loaded into ICs underlying layer of direct 68HC11 code, with user interface - IC binary (ICB) files installed in interrupt structure of 68HC11 Monitors shaft encoder values and calculates encoder steps and velocity needs quickly and at regular intervals HBs software libraries include set of routines for supporting shaft encoders for both positioncounting and velocity measurement. For each analog input on HB, a pair of shaft encoder routines is provided. Once loaded into IC, the encoder routines are automatically active; no additional commands are needed to turn them on. Each encoder0_counts variable (running total of transitions on encoder sensor) will automatically increment every time it senses a transition on its corresponding encoder sensor The encoder0_velocity value (velocity measurement) is continuously updated (copyright Prentice Hall 2001)

Programming Encoders /* Normal encoders, on ports 7 and 8. Must load encoders.lis to use this, more info in the HB manual. */ void main(void) { enable_encoder(0); /* Turn on encoder on port 7 */ motor(0, 20); while (read_encoder(0) < 130) ; reset_encoder(0); motor(0, -20); while (read_encoder(0) < 130)

; ao(); } /* Using encoders on analog ports 0 through 5 Must load the relevant file, sendr0.icb in this case. Consult the readme in the libs directory for info. */ void main(void) { motor(0, 20); while (encoder0_counts < 130) ; encoder0_counts = 0; motor(0, -20);

while (encoder0_counts < 130) ; ao(); /* Note that these analog functions also provide velocity information */ } Shaft Encoding Measuring Velocity Driver routines measure rotational velocity as well as position Subtract difference in the position readings after an interval of time has elapsed Velocity readings can be useful for a variety of purposes Robot that has an un-powered trailer wheel with a shaft encoder can easily tell whether it is moving or not by looking at encoder activity on the trailer wheel. If the robot is moving, the trailer wheel will be dragged along and will have a non-zero velocity. If the robot is stuck, whether or not its main drive wheels are turning, the trailer wheel will be

still. Velocity information can be combined with position information to perform tasks like causing a robot to drive in the straight line, or rotate a certain number of degrees. These tasks are inherently unreliable because of mechanical factors like slippage of robot wheels on the floor and backlash in geartrains, but to a limited extent they can be performed with appropriate feedback from shaft encoders. Shaft Encoding Reflective Optosensors as Shaft Encoders Its possible to build shaft encoders by using a reflective optosensor to detect black and white markings on an encoder wheel Wheels can be used with any of the reflective optosensor devices,

as long as the beam of light they generate is small enough to fit within the black and white pieshaped markings Shaft Encoding Opto-Electronic Computer Mice Common desktop mouse uses shaft encoder technology to figure out how the mouse ball is turned Two slotted encoder wheels are mounted on shafts that are turned by the balls movement On either side of each encoder wheel are the infrared emitter and detector pair Mice use quadrature shaft encoding, a technique that provides information about which way the shaft is turned (in addition to the

total encoder clicks) IR detector on each shaft actually has two elements, aligned so that as one element is being covered up by the leaf between the slots, the other is being exposed angular resolution of the shaft encoder 64 segment means 64 pulses per one complete revolution of the shaft. 1 revolution = 360o 1 revolution = 64 pulses 1 pulse = 5.625o (angular resolution) Increasing the number of segments, called the pulses per revolution (ppr) increases the angular resolution of the shaft encoder.

An Example Datasheet Connection to Handyboard Two shaft encoders can be connected to handyboard!!! Signal 5V Ground 1 0 Interactive C Functions Load encoders.lis first. void enable_encoder(int encoder)

enables the encoder(0 or 1) void disable_encoder(int encoder) disables the encoder(0 or 1) void reset_encoder(int encoder) resets the counter of encoder(0 or 1) to zero Interactive C Functions void read_encoder(int encoder) returns the number of pulses counted by the given encoder(0 or 1) since last reset or enable. Maximum number of counts is 32767, after that -32768, -327670 will come.

Some Important Remarks Use an encoder which has a Vin = 5V and Vsignal = 5V. Use incremental shaft encoder. To use more than 2 encoders(upto 6), you can use analog ports instead of digital ports. But you have to use a different encoder library available on the Handyboard web site. Kheper a Robot Anatomy of the

Khepera Microprocessor IR-Sensors Wheels & DC-Motors Insights of Khepera Microprocessor IR-Sensors Wheels & DC-Motors Simplified Braitenberg Algorithm

Obstacle on Left side? No Yes Obstacle on Right side? No Move Forward Yes Turn Right

Turn Left No Obstacle on Back? Yes End n 1002

353 331 287 265 243 221 199 177

155 925 No filter in Light 309 n 848 771 694

617 540 463 386 133 111 89 67

45 23 1 0 309 1200 1000 800 600 400 200

0 232 155 78 1 IR -va lu e s I R -v a l u e s No filter in Darkness

1200 1000 800 600 400 200 n 199 221

243 265 221 2 43 2 65 155 133 111 89 67

45 23 1 1 99 Averaging in Light 177 n 1 77

1 55 133 11 1 89 1200 1000 800 600 400 200 0

67 45 23 1 IR va lu e s IR v a lu e s 1200 1000 800 600

400 200 0 IIR filter in Light Results On darkness Slow filter response when approaching obstacle Even slower when moving away from obstacle On light Acceptable filter response time when approaching obstacle Acceptable filter response time when moving away from obstacle

Noisy readings greatly reduced Results (cont.) Satisfactory performance of Braitenberg algorithm without filtered readings on darkness Problems using filters with Braitenberg algorithm Robot slow to react to filtered sensory readings Conclusions Fluorescent light noise cause serious effects on Kheperas performance Digital filters proved to be useful in reducing noise in sensory readings

Filters performance are greatly affected by levels of ambient light Future Works Braitenberg algorithm modified to allows detection of ambient light Activate filters on high levels of ambient light Disable filters on low-light conditions Develop user-friendly program for testing algorithms and filters Shaft Encoder Exercises 1. Build a shaft encoder using a break-beam optosensor and a perforated disk or LEGO pulley wheel. Verify the raw sensor performancewhat values represent the light beam being broken vs. not broken? 2. Choose a suitable midpoint value for determining encoder transitions. Write a program in IC to implement

the simple encoder counting algorithm presented in the flowchart. Use IC multi-tasking capability to display the encoder counter variable while the counting routine is running, and experiment with the encoder. Can you determine the performance limit of the algorithm in your implementation, in terms of counts per second? What is a fundamental problem with this implementation method? 3. Load a library shaft encoder routine and experiment with its performance. Capture raw data from the encoder. Based on the graph of raw encoder performance, choose suitable high and low threshold values. Explain your choices. 4. One limitation of current encoder routines, both the IC and library versions, is that they cannot determine which direction the shaft is rotating. Can you think of a different approach for determining the direction of rotation? 5. Implement the trailer wheel idea discussed in the text on your HandyBug. Write a program to make HandyBug drive around and stop, back up, and turn when the trailer wheels velocity is 0. Can you think of other applications for knowing the robots velocity, other than as a non-zero/zero (i.e., moving/not moving) quantity? 6. Instrument one of HandyBugs drive wheels with an encoder, and write a program at attempts to maintain constant velocity on the drive wheel by varying the power level delivery to the motor. Experiment with the

system by holding HandyBug in the air and applying pressure to the drive wheel. Is the system able to maintain the velocity? What happens if you suddenly remove the pressure? Sources A. Ferworn Sal J. Vega Daisy A. Ortiz Advisor: Ral E. Torres, Ph.D., P.E. Maja Mataric Ali Emre Turgut Dr. Linda Bushnell, EE1 M234, [email protected] Web Site: Robotic Explorations: A Hands-on Introduction to Engineering, Fred Martin, Prentice Hall, 2001.

Creative Uses: IR Sensors Sharp IR sensors are very accurate and operate well over a large range of distances proportional to the size of a Lego robot. However, they have almost no spread. This can cause a robot to miss an obstacle because of a narrow gap. One solution is to make the sensor pan. One could also use a light sensor to detect obstacles indoors. Inside, there tend to be lights at many angles and locations. Thus, around the edges of most obstacles, a slight shadow will be cast. A light sensor could detect this shadow and thus the associated object. Warning: this could be a very fickle design. Touch sensors can have their spread increased with large bumpers, and can be used for wall following to implement bug2.

They are also dirt cheap. IR Sensors 750 nm to 1,000,000 nm Transmitters (LEDs or thermal) Detectors (photo diodes, photo transistors) IR: Three common strategies IR Rangefinders What sorts of techniques can we use? Time of Flight (TOF) Signal Strength Triangulation

Creative Uses: IR Sensors Example of sharp IR mounte sweep for a wider field of vi Shadow cast indicates obstacle: one way to navigate with photo resistors. Intensity Based Infrared voltage Increase in ambient light raises DC bias time

voltage Easy to implement (few components) Works very well in controlled environments Sensitive to ambient light time Modulated Infrared amplifier bandpass filter integrator limiter demodulator comparator

Input Output 600us 600us Insensitive to ambient light Built in modulation decoder (typically 38-40kHz) Used in most IR remote control units ( good for communications) Mounted in a metal faraday cage Cannot detect long on-pulses Requires modulated IR signal

Digital Infrared Ranging Modulated IR beam Optical lenses +5v output input 1k 1k gnd position sensitive device (array of photodiodes) Optics to covert horizontal distance to vertical distance

Insensitive to ambient light and surface type Minimum range ~ 10cm Beam width ~ 5deg Designed to run on 3v -> need to protect input Uses Shift register to exchange data (clk in = data out) Moderately reliable for ranging Polaroid Ultrasonic Sensor Mobile Robot Electric Measuring Tape

Focus for Camera Theory of Operation Digital Init Chirp 16 high to low -200 to 200 V Internal Blanking Chirp reaches object 343.2 m/s Temp, pressure Echoes Shape Material Returns to Xducer

Measure the time Problems Azimuth Uncertainty Specular Reflections Multipass Highly sensitive to temperature and pressure changes Minimum Range Beam Pattern Not Gaussian!! (Nave) Sensor Model Problem with Nave Model

Reducing Azimuth Uncertainty Pixel-Based Methods (Most Popular) Region of Constant Depth Arc Transversal Method Focusing Multiple Sensor Certainty Grid Approach Combine info with Bayes Rule (Morevac and Elfes) Arc Transversal Method

Uniform Distribution on Arc Consider Transversal Intersections Take the Median Mapping Example Vendors Micromint Wirz Gleason Research (Handyboard) Polaroid-oem

Metal Detector Oscillator signal coupled via transformer When T2 is turned off, T3 is turned on 112kHz LC Oscillator LED will drop about 2volts Diode converts AC signal to DC ripple and applies as bias to T3 9v Signal to 5v logic

+9V +5V Rpullup 9v signal + - PIC LM311 comparator A comparator can be used to convert a two-state signal to digital logic

When the + voltage is above the voltage on the - pin, the output is high When the + voltage is below the - voltage, the output is low The LM311 has an open collector (you need to provide pullup resistor) This allows conversion from 9volt logic to 5volt logic MASLab Sensors January 2002 Christopher Batten Agenda Quadrature phase sensors Sensors, in general The specific kinds of sensors in 6.186 Quadrature Phase

Encoders We have a precise method of measuring how much our wheels rotate How can we use this for navigation? Pitfalls? Slippage Inaccurate characterization Odometry Use odometry to find out how far each wheel has moved in some (short) time interval. Assume that robot was turning at a constant rate during this interval. y (xk,yk)

k x Odometry the model y About how far did the robot actually go? k+1 (xk+1,yk+1) Dk=(dL+dR)/2 The angle of the sector?

dR k k=(dR-dL)/B dL xk+1=xk+Dkcos(k+ k/2) yk+1=yk+Dksin(k+ k/2) (xk,yk) k x k+1= k+ k

Try this at home! B is the baseline- the distance between the two wheels. Odometry- Coping with Error Odometry, by itself, will get worse and worse Try to reconcile/confirm results with other navigation methods: Range to objects Angles to objects, targets, waypoints, beacons Any other ideas? 6.186 - Sensors What is a sensor?

Common types: Infra-Red (IR) Ultrasound Physical contact Other types: Magnetic field detectors (Reed switches) Be creative! Infrared Beacons Custom hardware specifically designed for MASLab IR Beacon Transmitters broadcast data packets containing a unique ID number (waypoints, targets, navigation beacons)

IR Beacon Receivers are directional and look for ID broadcasts to identify the direction of a specific beacon (one per team) Infrared Beacons Transmitters Which IDs correspond to waypoints, targets, and navigation beacons is predetermined and will not change The location of any beacon (in relative or absolute coordinates) is not known ahead of time Transmitters broadcast their ID in eight different directions IR Beacons will be either 10 or 8 and the walls will all be

9 Infrared Beacons - Receivers Receivers can receive packets in two opposite directions combined with 180 servos this provides 360 listening Beacons do not (directly) provide any information concerning the distance to the beacon (use triangulation or range sensors) Range is approximately 15-20 feet and should be Receiver able to receive approximately 5 packets perw/ Baffle Receiver w/o Baffle second.

Each team is responsible for making their own baffles. Infrared Range Detectors Sharp GP2D12 IR range detectors Two per team (more upon request) Sensor includes: Infrared light emitting diode (IR LED) Position sensing device (PSD) To detect an object: IR pulse is emitted by the IR LED Pulse hopefully reflects off object and returns to the PSD

PSD measures the angle at which the pulse returns Position Sensing Device Uses small lens to focus reflected pulse onto a linear CCD array LE D PS D LE D

PS D Infrared Range Detectors 3 Analog Output Voltage (V) 2.5 2 1.5 1 0.5 0

Distance to reflected object (in) Theoretical Range: 4in (10cm) to 31in (80cm) Actual Range: ~4in (10cm) to ~ 18in (45cm) Infrared Range Detectors Detecting Targets Placed target in various positions in front of a standard MASLab wall Relatively narrow field-of-view Noise Output voltage follows normal-like distribution with constant std dev User-level averaging may be

useful Sampling Sensor refreshes approx. every 32ms Can reasonably acquire 20 samples per second 0.45 0.45 0.45 0.44

0.45 0.45 2.40 1.05 0.69 0.44 0.45 0.45

0.45 0.45 0.45 0.5 ft Infrared Range Detectors Uses Short range obstacle mapping - Mount sensor on servo and collect range data for various angles Bump sensors - Threshold output voltage, Use multiple sensors at appropriate angles to cover more area Target detection - Arrange multiple sensors to

detect shape of waypoints and targets Final practical concerns Place a 10-20uF capacitor between Vcc & GND Position IR sensors to avoid dealing with < 4in readings Autonomous robotics based on simple sensor inputs. Stuart Dodds Abstract A robot is explained as a device that performs functions normally ascribed to humans Webster.

Autonomous means that the robot can work totally independently of itself, once it has been programmed, and it should be able to function without interaction from any human influence. Many robots are used nowadays to work in conditions where it is inaccessible for humans to work and therefore need to be autonomous. The aim of this project is to program a robot (shown left) using PIC (peripheral interface controller) chips, so that it will utilise its infra red sensors and run its stepper motors to follow a boundary wall within an enclosed environment. Infra-Red Sensors Environment Sensor Range Boundary

This diagram is a depiction of an environment that has been built to test the robot with a selection of acute, obtuse and reflex angles. There are 13 Infra Red (or IR) sensors attached to the front half of OFF OFF the Robot that are used to detect the OFF environment boundary. These Sensors ON sensors are light sensitive and ON output a signal when they become

active. The sensor range is approximately 15mm which gives the robot enough time to read the information, decide on what to do and stop before it hits the boundary. Stepper Controller Stepper Motors IR Sensor Controller PIC 16f84 Pulse Direction Pulse Direction

Further Work PIC 16f84 Communication lines B0 A0 B1 B3 B2 B4 Starting Point

B2 B5 A0 A1 A2 A3 Data Selector S0 Sensors S1

S2 S3 Multiplexer As shown the robot follows the same sequence as it travels round the environment. When it reaches a wall the robot will stop then start to rotate until non of the sensors are active. Then it will move forward for a designated amount of time and rotate right and move forward again to look for the wall. B0

Any Sensor Active B1 Sensor Data 13 The devices that run all the computations of the robot are two PIC chips. One chip receives information from the IR sensors then executes an algorithm on this data. It then sends instructions to the other chip which controls the stepper motors. Now that the robot works properly and has been thoroughly tested using the IR sensors, the next stage of development is to implement a set of line

following and ultra sonic sensors. This involves adding two more PIC chips to the circuit board, then to program them so they can read and process the information from these completely different sensor types. Once all of these have been fully implemented and tested I shall run a comparison between all three of them. Infra-Red Sensors There are 13 Infra Red (or IR) sensors attached to the front half of the Robot that are used to detect the environment boundary. These sensors are light

sensitive and output a signal when they become active. Sensor Range Boundary OFF OFF OFF ON

Sensors ON The sensor range is approximately 15mm which gives the robot enough time to read the information, decide on what to do and stop before it hits the boundary. Environment This diagram is a depiction of an environment that has been built to test the robot with a selection of acute, obtuse and reflex angles. As shown the robot follows the same sequence as it travels round the environment. When it reaches a wall the robot will stop then start to rotate until non of the sensors are active. Then it will move forward for a designated amount of time and rotate right and move forward again to look for the wall.

Starting Point Stepper Controller IR Sensor Controller PIC 16f84 Stepper Motors PIC 16f84 Communication lines Pulse

Direction Pulse Direction B1 B0 B2 A0 B5 B3

Any Sensor Active B2 B4 A0 B0 A1 A2 B1 A3

Data Selector Multiplexer S0 Sensors S1 S2 Sensor Data

S3 13 The devices that run all the computations of the robot are two PIC chips. One chip receives information from the IR sensors then executes an algorithm on this data. It then sends instructions to the other chip which controls the stepper motors. The Robot - Khepera To make gas sensor move freely indoor. Khepera basic module and its General I/O extension module will be used in our experiment. It features: - a diameter size of 5cm

- 2 independent DC motors with encoders - 8 infra-red sensors - An onboard 68331 microcontroller - An onboard battery - A modular design with extension modules Khepera Basic module General I/O extension module The general I/O is a turret that can be plugged on the basic configuration making simple custom electronic extensions possible. It features: - Digital inputs and outputs - Power outputs - Analog inputs with adjustable gain - Pass-through K-bus to other turrets

General I/O Turret SENSOR The Sharp GP2D02 IR Distance Measuring Sensor Quick Overview Sensors are utilized for many types of detection schemes. Such as: light intensity, temperature, etc For our purpose: Distance Examples

Tactile Bumpers (simple sensor) designed to form a contact closure when pressure is applied to the bumper other actuators can be used to trigger control or decisions concerning course of action. Optical Proximity Sensors (photoelectric sensors) Three groups Opposed: electric eye; emitter/detector beam interruption Retro-reflective: uses an object to reflect from emitter to the detector Diffuse: uses the target object to return the energy from the emitter to the detector

GP2D02 SENSOR Measures distance in range from 20 to 80cm. Designed to interface to small micro-controllers. Its relatively insensitive to the color and texture of the object at which it is pointed. Low current consumption at stand-by mode (Approximately 3 A). Actual Sensor Size Distance Measurement by

Triangulation IR LED Transmits a bundled beam to the object plane. Reflected beam is receive by the photo detector(PSD). The angle of the received beam depends on distance of the object plane. Two Different Object Planes Structure of Photo Diode N-conductive

substrate layer is an isolation layer P-conductive layer is embedded in isolation layer from IR irradiated Contact of the player is made on left and right side Structure of a position sensitive photo diode(PSD) How PSD Measures Distance? Spot irradiation in the center of the player, both currents I1, I2 will have same value. Spot irradiation goes to the right, the I1

will decrease and I2 will increase by the same amount. The difference between the I1 and I2 will give the location of a spot irradiation on PSD. PSD Continued Diodes in the Op-Amps feedback give a logarithmic behavior to the I-to-V conversion circuit. Collector current, Ic, in each Op-amp is identical to the I1 and I2. Third Op-Amp processes

the difference of the two output voltages from previous Op-Amps. Vo =VT. ln(I1/I2) Circuit for position sensitive Current-to-voltage conversion Distance Chart Distancevs. irRangeValue 300 250 150 100 50

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

irRangeValue(int) 200 Distance(inches) Timing When interfacing with any type of hardware, timing is an issue. Vin and Vout are control measurements. Vin drops to low for minimum 70ms. IR LED transmits 16 pulses

towards the object. Mean value of 16 measurements reduces possible errors. Timing Diagram for Measurement and data handling Configuration Sensor has four pins for electrical contact. Pin 2 (IN) from the sensor connects to IR OUT.

Pin 4 (Signal) from the sensor connects to IR IN. Pin 1 and 3 are connected to ground and +5V, respectively. SW1 and SW2 refer to bumper switches. Handy Board Connection Example of Control Program int distance = 1; /* Init and set the variable distance to 1 */ void range() {

while(1) { sleep(.30); /* Wait .3 seconds, without updating irRange */ pulse(1); /* Update irRange to new detected distance */ distance = irRange; /* set variable distance equal to irRange */ } } Continue void escape() { while(TRUE) { if(distance >= 150)

{ /*If IR sensor detects object within a close proximity take evasive action*/ escape_output_flag = TRUE; printf("STATUS = IR SENSE \n"); sleep(2.0); printf("\n"); escape_output= -30; escape_output1= -30; sleep(6.0); escape_output= -60; escape_output1= 115; sleep(10.0); escape_output= 30; escape_output1= 30;

sleep(2.0); escape_output= 30; } escape_output_flag = FALSE; } } BREAK TIME Any Questions So far? OK! LETS MOVE ON TO THE LAB! Lab Exercise

Lab Objective: Load pulse.icb , which is a compiled assembly object file. Pulse.icb enables 2 interactive C functions pulse() and irRange Every time you want the IR sensor to obtain a position, call the pulse subroutine, the position integer is updated in the variable irRange. Continue Exercise: Write a behavioral program, using your bumper switches and the new IR sensor to avoid obstructions. Upon pushing the START button, the robot moves forward and stops after 3 minutes or the STOP button is pushed.

After IR detector detects an obstruction: Backup a quarter of the length of your robot using the IC time commands, storing any constants set as persistent global variables for use in later programming (see page 12 of the Handy Board manual). Turn 45 degrees in either direction and continue forward. IR Communication Modulated infra red can be used as a serial line for transmitting messages. This is is fact how IR modems work. Two basic methods exist: bit frames (sampled in the middle of each bit; assumes all bits take the same amount of time to transmit) bit intervals (more common in commercial use; sampled at the falling edge, duration of interval between sampling determines whether it's a 0 or

1) Notes: you are strongly encouraged to pay careful attention to the exercises and problems given in your assigned readings. Projects, exams, homeworks and reports will use some of those, so it is in your interest to think about the answers to their questions, and work some of them out as practice. Also the additional recitations (Fridays) problems may appear on the exams.

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