1. SENSORY DEVICES
Why do we need sensory device for robot? Robot must gather extensive information about their environment in order to function properly. Not only about environment but also about itself (e.g. the status of links and joints of the manipulator)

2. SENSORY DEVICES
The end-effector and sensors work in coordination with the robot controller.

3. SENSORY DEVICES Major functions of sensors in robot: Status sensors
Environment Sensors
Quality Control sensors
Safety sensors
Workcell control sensors (industrial robot)

4. SENSORY DEVICES STATUS SENSORS
Sense position, velocity, acceleration, and/or torque/force at each joint of the manipulator.
Also called as Internal Sensor.
Degree of accuracy depend on the accuracy and resolution of internal sensors.
Must be cost effective because internal sensors are required for each axis of the manipulator.

5. SENSORY DEVICES ENVIRONMENT SENSORS
Extract features of the objects in the surrounding environment of the robot.
Also called as external sensors because they are generally placed external to the manipulator (some exception, writs force-torque sensor).
Real-time processing.

6. SENSORY DEVICES QUALITY CONTROL SENSORS
Sensors can be used to determine a variety of part quality characteristics.
The external sensors used for environmental feedback could also be used for detecting faults and failures in the finished product.

7. SENSORY DEVICES SAFETY SENSORS
Important function of this sensor is for safety and hazard monitoring.
Applying brakes to robot when there is an electricity failure so that robot structure will not fall to zero gravity position and injure nearby human.

8. SENSORY DEVICES INTERLOCK IN WORKCELL
A situation that requires sequencing of tasks such that completion of a task must be ensured before proceeding to the next task.
Part must arrive on conveyor before the gripper of the manipulator can pick it.

9. SENSORY DEVICES
What are the problem in robot sensing? Even a simple sensing task is quite complex when applied to robot. Limited by sensor capabilities. Properly choosing sensor is essential part in robotics.

10. SENSORY DEVICES
5 important characteristics of any sensing devices: Range Minimum and maximum change in input signal to which the sensor can respond. The sensor could possess a wide operating range. Response The sensor should be capable of responding to changes in the sensed variable in minimum time. Ideally, the response should be instantaneous.

11. SENSORY DEVICES
5 important characteristics of any sensing devices: Accuracy How close the output of the sensor is to the expected value. As high as possible. The output should properly reflect the input quantity being measured or sensed. Sensibility It refers to the change in the output exhibited by the sensor for a unit change in input.

12. SENSORY DEVICES
5 important characteristics of any sensing devices: Linearity Exhibit the same sensitivity over its entire operating range. Others The device should not disturb or have any effect upon the quantity it senses or measures. The device should be suitable for the environment in which it is to be employed. The device should include isolation from receiving excess signals or electrical noise that could give rise to the possibility of mis-operation or damage of the sensor , circuit or system.

13. SENSORY DEVICES
Other important characteristics of any sensing devices: Reliability How many time it operates properly divided by how many times it is tried. Repeatibility The output of the sensor may be different each time it is measured. Respond Time A time required to observe the change in output as a result of the change in input.

14. SENSORY DEVICES
Other important characteristics of any sensing devices: Interfacing The interfacing between sensor and other devices become an important issues if they do not match or if other add on circuit become necessary. Type of output (digital or analog) The output of the sensor may be different each time it is measured. Weight, Size Cost

15. CLASSIFICATION OF ROBOTIC SENSORS
Status Sensor
(Detect position, velocity, acceleration, torque ,force)
Environment Sensor
(Detect presence, motion,force,torque, Touch/tactile, etc)
Potentiometer, Tachometer, Optical Encoder, Microswitch, etc.
Contact Sensor
Noncontact Sensor
Pressure, force, slip, torque,surface finish, temperature, pH, etc.
Vision, optical, acoustic, infrared, proximity, range, temperature, chemical, etc.

16. KINDS OF SENSORS IN ROBOTICS
Acoustic Sensors
Acoustic distance sensors work by transmitting an acoustic signal (sound) and "listening" for the reflected signal. The delay associated with reception of the reflected signal can be correlated to the distance of the reflecting object. Acoustic sensors generate a signal by moving a diaphragm quickly back and forth displacing the air around the diaphragm, creating an acoustic wave.
Acoustic distance sensors usually operate at ultrasonic frequencies ( kHz). Ultrasonic sensors are very good at detecting objects, that are relatively large compared to ultrasonic wavelengths (~1cm). Ultrasonic signals propagate in air, so acoustic sensors may not be reliable in situations where the air is moving at a high speed unless the air speed can be measured and compensated for. Acoustic sensors also have difficulty making a reliable measurement in acoustically noisy environments.
Operate at ultrasonic frequencies (40-250kHz)
Good at detectin g Object large compare to ultrasonic wavelength (~1 cm)

17. KINDS OF SENSORS IN ROBOTICS
Proximity Sensors
"Proximity Sensor" includes all sensors that perform non-contact detection .
Proximity Sensors are available in models using high-frequency oscillation to detect ferrous and non-ferrous metal objects and in capacitive models to detect non-metal objects.

18. FORCE SENSING IN MEDICAL ROBOTICS
Minimally Invasive Direct Coronary Artery Bypass (MIDCAB)
Robotic MIDCAB

19. FORCE SENSING IN MEDICAL ROBOTICS
Disadvantage of conventional Minimally Invasive Surgery (MIS)
Reduced dexterity of the surgical tools.
Reversal of directions in vivo due to fulcrum effect created by the constraint of the small insertion hole.
Inability to directly visualize the operative site.

20. FORCE SENSING IN MEDICAL ROBOTICS
Without force sensors,
Sensing the tool-tissue interaction remotely (outside the body) & manually is impaired by the tool friction insertion port, inertia of the tool shaft, reaction forces between tool shaft and insertion point.
Surgeon losses ability to perform an organ palpation (examine or explore by touching, common practice during open surgery) for the detection of abnormalities including tumors, nerves, vessel, or tissue stiffness variation.
Factors impairing force sensing manually – friction, inertia, reaction forces.
Remotely detect abnormalities inside body without force sensor is difficult.

21. FORCE SENSING IN MEDICAL ROBOTICS
Applied force of medical robot with motor actuated joint, could be determined by measuring the current of the motor. The current of the motor is proportionate to the armature current of the motor. Also called as electrical based sensing method.
Some researchers have established this force sensing technique for medical robots, however, the friction of joints, inertia of all linkages, backlash, nonlinear effects including the change of motor brush conductivity & winding resistance, good accuracy of force sensing was not achievable.
Electrical based – easy but many problems.

22. FORCE SENSING IN MEDICAL ROBOTICS
For tool driven by pneumatics actuators, pressure based sensing method was used to estimate force at end effector which provide high accuracies and sensitivities.
Another way of sensing the force is using the strain gauge and it is known as resistive based sensing approached. The stiffness of the structure where the strain gauge was placed affects the sensitivity of the strain gauge sensing. The stiffer the structure of the tools is, the lower the sensitivity of the force measurement.
Strain gauge – advantages unknown, problem – stiffness.

23. FORCE SENSING IN MEDICAL ROBOTICS
If better sensitivity is essential, capacitive based sensing is much more sensitive than the resistive based sensing. Moreover, small size and high resolutions in detecting force signals, and its adequate distribution over all cells of the array, this sensor is attractive for the integration with MIS device including the miniature surgical manipulators and catheters.
Capacitive strain gauge – smaller size, high resolution in detecting force signal.

24. FORCE SENSING IN MEDICAL ROBOTICS
Optical based approach of force sensing
LED emit light, receive by the Photodetector.
Aircushion was provided by airflow enables the sphere to be rolled on the soft tissue.
When the sphere is force to roll on the soft tissue, the reaction forces from the soft tissue will push the sphere upwards. This will interrupt the light emitted from LED to the Photodetector. The intensitiy of the light signal is then modulated in proportion to the tissue interaction forces. The force applied to the tissue can be adjusted by altering the flow rate of air passing through the shaft.
Optical based – minituarization, can be used with MRI.

25. FORCE SENSING IN MEDICAL ROBOTICS
Optical based approach of force sensing
Miniaturerization in MIS, optical based sensor used optical fibre to transmit light over large distance. In this case, the optic signal is modulated by a reflector which was attached to a flexible structure. When force applied caused the flexible structure to deform, there reflector position is changed and the magnitude of force is modulated.

26. FORCE SENSING IN MEDICAL ROBOTICS
Optical based approach of force sensing
Miniaturerization in MIS, optical based sensor used optical fibre to transmit light over large distance. In this case, the optic signal is modulated by a reflector which was attached to a flexible structure. When force applied caused the flexible structure to deform, there reflector position is changed and the magnitude of force is modulated.

27. FORCE SENSING IN MEDICAL ROBOTICS
Optical based approach of force sensing
The benefit of optical based sensor is that they can be used with MRI. MRI use magnetic and radiofrequency fields, sensor operate with electrical signal cannot be used in MR environment. MRI guided robotics system use optical based sensor.

28. CHOOSING THE RIGHT SENSOR
Guidelines:
Analyze the nature of the information needed.
Find what kind of information will be provided by the sensor.
Determine how the sensor signals will be used.
For the variable to be sensed, determine
Nominal value , range of values, accuracy required, required reliability, speed of measurement and etc.
5. Estimate the environmental variations under which the sensing is to be done.
6. Examine the nature of task dependent on the sensed signals, for example, critical tasks require reliable sensing.
7. Also consider other factors:
Sensitivity, linearity, within desired range, maintainability, life, power consumption, ruggedness, availability and cost.
More than one way to sense, the optimum sensor should be deployed

29. CHOOSING THE RIGHT SENSOR:MEDICAL ROBOT
Additionally,
Size limit.
Sterilizability.