Sensors Sensors Sensors changes a robot from dumb

Sensors

Sensors • Sensors changes a robot from dumb to intelligent. – The ability to adapt to particular surroundings is one definition of intelligence.

Classes of Sensors • Sensors for robots can be divided into three classes: – internal sensors, – external sensors, – interlocks • Most sensors are some type of transducer. – E. g. The ear converts sound energy into electrical signals.

Internal Sensors • • • Limit switches Haptic perception Governor Lead screws Shaft-encoder Direct-readout encoders or absolute-readout encoders

External Sensors • Microswitch or pressure sensor • Photoelectric device

Interlocks • Interlocks are devices that do not allow an operation to be performed until certain conditions exists. • Can be internal or external.

Sensor Areas for Robots • • Vision Touch Range and proximity detection Navigation Speech output Speech input Smell

Vision • Present-day industrial robots use vision to locate and orient parts.

Limits of Robot Vision • The robot grasps a part or parts from the bin. • The robot places the parts on a table that has an artificial skin surface. • The skin locates the orientation of the parts. • The robot is instructed in how to grasp the part with proper orientation for the rest of task. Week No 10 9

Touch • Tactile sensing, the sense of touch for robots, is needed if a robot is to perform delicate assembly operations. • When a robot touches something, force is reflected back through each joint. • In screwing nut and bolt, touch is more imp then vision.

Types of Touch Detection • Single-point detection • Simple edge detection • A multiple-point shape detector

Range and Proximity Detectors • Range Detector detects objects situated at some distance from the robot. – Non-contact devices • Laser, radar, sonar, vision and infrared devices. • A proximity detector detects objects in the immediate vicinity of the robots. – can be contact or non-contact devices. • E. g. A magnetic detector

Speech Output • Speech output is not handled by sensor. • It allows the robot to communicate with us through additional sensor of our hearing. • Voice output is often used in conjunction with voice input to confirm that the robot understands a voice commands. Week No 10 13

Speech Output (Contd. . . ) • A robot using voice output may not even be heard. • Voice output is a valuable safety feature when robots are used in offices or hospitals. • The use of robots by disabled people is easier if a robots has a voice. Week No 10 14

Speech Output (Contd. . . ) • Voice output is also useful in medical robots for the disabled people who cannot speak. • Voice output, voice synthesis or speech synthesis for a robot can be accomplished by three different methods. Week No 10 15

Speech Output (Contd. . . ) • The oldest method is to have a human record the desired words, phrases, or sentences on individual pieces of magnetic tape. • A computer or robot then plays back the appropriate piece of tape to produce the desired message. • Because this method plays back the real human speech, the individual words sound very natural. Week No 10 16

Speech Output (Contd. . . ) • The second method of voice output involves having a human speak the words into a microphone. • A computer stores each word digitally, and this digital information is then converted back into analog speech one word at a time, as the computer or robot speaks. • This method tend to sound very much like a human speaker. Week No 10 17

Speech Output (Contd. . . ) • The third method of voice output constructs speech from stored phonemes for the English language. • This method tends to sound very mechanical. • There is no emotion or inflection in the speech. • The frequency of the speech can be changed as though it were being said by man, or woman. Week No 10 18

Speech Output (Contd. . . ) • Adding an inflection or emotion content circuit to the speech synthesizer would make it much more acceptable to human. . Week No 10 19

Speech Input • Voice input commands is not practical in noisy factory. • Voice input has become highly desirable. • The area of sensory input interpretation is one that will benefit with the advances greatly in artificial intelligence. Week No 10 20

Speech Input (Contd. . . ) • Robots can use speech input by the use of microphone. • This speech information can be converted into digital forma nd stored in robot’s memory. • Most speech recognition systems now in use recognize a very small vocabulary. Week No 10 21

Smell • Industrial robots of today do not have the sense of smell. • Sensors already exist that can detect nitrates and explosives. • Smoke detectors can react to the particles in the air. • Exhaust gas analyzers are available for checking car exhaust emissions. • The military has sniffers, for detecting unauthorized people. Week No 10 22

Smell • Domestic robots could use synthetic noses for detecting natural gas leakage from a water heater or owen or a freon leak from a refrigerator or air conditioner. Week No 10 23

Noise Issues • Real sensors are noisy • Origins: natural phenomena + less-than-ideal engineering • Consequences: limited accuracy and precision of measurements • Filtering: – software: averaging, signal processing algorithm – hardware tricky: capacitor

Electrical Noise and Sensor Information • Generally robot works with a high level of noise. • This noise is created by the machinery around the robot and by robot itself Week No 10 25

Electrical Noise and Sensor Information (Contd. . . ) • The memory and control circuits in a robot’s controller respond to a signal which is millionth of a second. • A burst of electrical noise lasts long enough to change the controller’s memory and mislead what is supposed to be doing. Week No 10 26

Electrical Noise and Sensor Information (Contd. . . ) • What can we do to eliminate this electrical noise? Week No 10 27

Electrical Noise and Sensor Information (Contd. . . ) • The power supply of the motors should be separate from power supply of controller and sensor. • The wiring for the motors should be separate from and round separately from the wiring for controller and sensor. • We can use shielded cable or wires for all wiring of the controller, signals and the sensors. Week No 10 28

Electrical Noise and Sensor Information (Contd. . . ) • If controller and manipulator are not contained in the same area connecting wires must be run between the two devices. • The farther apart the two devices are physically, the better antenna the wiring makes for picking up electrical noise from the robot and from surrounding machinery. Week No 10 29

Electrical Noise and Sensor Information (Contd. . . ) • The noise problem will be greatest, if point to point wiring is used. • Point to point wiring uses individual wires from one point on the circuit to the other point on the circuit. Week No 10 30

Electrical Noise and Sensor Information (Contd. . . ) • The noise is decreased by using twisted pairs of wires, wires run on pairs from one point to another in a circuit with one of the two wires in each pair grounded. Week No 10 31

Electrical Noise and Sensor Information (Contd. . . ) • The noise is lowest if shielded wires are used. • Each wire have a grounded shield surrounding the wire. Week No 10 32

Electrical Noise and Sensor Information (Contd. . . ) • Signals transmitted at low level of voltages. • The lower the voltage level the greater will be the noise effect. Week No 10 33

Electrical Noise and Sensor Information (Contd. . . ) • A signal can be send over a distance by using differential signal. • This uses differential drivers and receiver circuits. • The signal is sent over two wires. • Voltage level is not what it sensed on either wires, but the difference in the voltages between the two wires. Week No 10 34

Electrical Noise and Sensor Information (Contd. . . ) • This type of transmission also tends to cancel the electrical noise, because such noise is picked up equally in both wires. • Another form of signal transmission that is unaffected by electrical noise is fiber optics. • The signals are light beams sent along an optical fiber. Week No 10 35

Electrical Noise and Sensor Information (Contd. . . ) • Noise in a signal can cause serious safety problems, some type of signal error detection should be used. • This may mean adding extra information to a signal to determine weather it has been changed. Week No 10 36

Electrical Noise and Sensor Information (Contd. . . ) • We can check the signal, by sending it more than once. • A human being reduces the probability of information errors by sending information over more than one path. Week No 10 37

Electrical Noise and Sensor Information (Contd. . . ) • It is easier to obtain sensor information, than to interpret it. Why? Week No 10 38

Electrical Noise and Sensor Information (Contd. . . ) • Most sensor interpretation is currently done through the software of an electronic computer. • The robot’s controller is not yet powerful enough to do its own interpreting. • Especially for vision system. Week No 10 39