Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Sensors and Vision Limit Switches • Provide information about the state or position of objects that concern the robot. • A device activated by contact with an object that changes the state of its contacts when the object exerts a certain amount of force. • The limit switch consists of a body, which houses and protects the electrical contacts, and some type of actuator, which moves with physical contact. • Actuators can use pressure or rotational motion to change the contacts of the switch. • When selecting a limit switch, you will need to know how much amperage the contacts must handle, how fast the switch needs to respond, and how much force the object contacting the limit switch can generate. • Each switch takes a certain amount of time to make (activate) or break (deactivate), so make sure that the switch can respond fast enough for the conditions under which you will use it. • Limit switches are used to prevent the robot from traveling too far, monitor the doors on safety cages, confirm raw parts ready for loading, verify that the machine the robot works with is in position, and to answer yes/no type questions. Proximity Switches • A solid-state device that uses light, magnetic fields, or electrostatic fields to detect various items without the need for physical contact. • A solid-state device is a unit made up of a solid piece of material that manipulates the flow of electrons without any moving parts so it doesn’t wear out. • Downsides to solid-state devices: – They never fully stop the flow of electrons. – They are vulnerable to electromagnetic pulses and other strong magnetic fields. • Main reasons that prox switches fail: – Physical damage to the switch. – Voltage that is greater than the prox’s voltage rating. Inductive Proximity Switch • Uses an oscillating magnetic field to detect ferrous metal items. • When a metal part enters the magnetic field of the inductive prox, it generates eddy currents in the part, which takes energy away from the magnetic field created by the oscillator in the prox. Capacitive Proximity Switches • A switch that generates an electrostatic field; working on the same principle as capacitors, it uses the item sensed to complete the capacitive circuit as well as sense materials at various distances. • The capacitive prox will interact with materials that are both magnetic and nonmagnetic. • The capacitive prox works just the opposite of the inductive prox in that the oscillation of the circuit begins when the item sensed enters the electrostatic field, and it dies off when no object is present. • The field on the inductive prox does not change, due to the construction of the switch, while the capacitive prox has an adjustment on the switch that allows the user to vary the electrostatic field and change the distance from which it interacts with objects. • It is possible to set the switch to detect items inside cartons, boxes, or other packaging materials. Photoelectric Proximity Switch • Detects levels of light, senses objects via reflected or blocked beams, and detects colors via an emitter that sends out a specific wavelength of light and a receiver that looks for that wavelength to return after it has interacted with the surrounding environment. • With the light level detection photoelectric switch, we can tune out or ignore the background, differentiate between parts on a background, and even detect transparent objects. • With proper calibration, this switch could monitor the empty spaces between parts on a conveyor line. • The color detection photoelectric prox switch analyzes the light coming into the receiver to determine color or color difference in parts. • Roboticists have used this sensor to tell the difference between blue and red balls, follow colored lines, and carry out other such tasks involving color recognition. • Drawbacks: – Changes in the ambient light will change the light returning to the switch and the reading, thus requiring recalibration – It has a set operating range that is dependent on the strength of the emitter and the wavelength of the light sent out. Tactile and Impact • Tactile – the ability to sense pressure and impact • Tactile sensing is about determining how much force is being applied, what the shape of the part is, how it is gripped, if the part is hot or cold • Impact – a robot’s contact with an object in the intended movement path • Impact sensing is concerned with detection of collisions, determining if forward movement is impeded or stopped, and shutting down or modifying the motion of the system to prevent damage to whatever is hit and the robot. • Complex tactile sensors use arrays or organized groups of sensing elements to gather information about contact with objects. • Simple systems consist of elements that have a digital type of output, either on or off, 1 or 0. • With this type of sensor, the system knows if it is gripping the part or not and how many elements are involved in that grip, denoting the surface over which the force is applied, but it has no data on the amount of force the system is using to grip the part. • High-end complex tactile sensors not only give information about contact with the part, but also how much force the system applies to the part. • Some even measure the temperature of the part it contacts. • The common factor in voltage, resistance, capacitance, and magnetic flux is that change in the shape of the element causes a change in the output of that element. • Calibration is a specified process that ensures that a precision system performs properly and provides for any adjustments needed. • Impact detection play a crucial role in minimizing or preventing damage to the robot as well as equipment and people around the robot. • Today, we typically monitor the amperage the motor uses or insert sensing devices designed to detect impacts. • Anything that causes the motor to use excessive amounts of current, such as a too-heavy load, bad bearings, friction, caked dirt in the joints, or something else requiring more force, can cause an impact alarm. • No matter how we detect the impact, the robot has to do something to prevent or limit the damage caused. • One of the tactics is to E-stop the robot and lock it in place. • Robots now disengage the motor from the joints until the system can come to a full stop to reduce the force the robot has to stop, reduce the energy of the impact, and reduce the stress on the robot’s internal systems. Position • Open-loop system – a system that assumes that everything is working correctly because there is only limited information on a few positions or no feedback at all to confirm everything is working as directed. • Closed-loop system – a system that sends out the control pulse to initiate movement and then receives a return signal that confirms movement, often including the direction, speed, and distance moved. Motor Encoders • Devices that directly monitor the rotation of a motor shaft and turn that information into a meaningful signal. • The robot controller uses this signal to determine what the motor is doing as well as when it has reached the desired point. • Hall effect sensor - a sensor that uses a magnetic field to cause voltage flow in a semiconductor used to track rotation. Incremental Optical Encoders • Consist of a disk that has either holes for light to pass through or special reflectors to return light, an emitter, a receiver, and some solid-state devices for signal interpretation and transmission. • The transmitter sends out light, and the light either passes through the holes or reflects back to the receiver, triggering the electronics of the encoder to send a signal back to the controller. • By adding a second row of reflectors or light windows, offset from the pulse count, and the appropriate emitter and receiver, we can now determine the direction of rotation by comparing the signals from the two rings. Absolute Optical Encoder • Adds enough emitters and receivers, usually four or more, to give each position of the encoder its own unique binary address. • When using these encoders, the robot knows where the motor is at any given point. • These encoders cost more, have more internal parts, and require more of the controller’s processing power. • The biggest enemies of encoders are oil, metal chips, shavings, or any other containment that gets inside the unit and either clouds the disk that interacts with the light or damages it. Global Positioning System (GPS) • A system that determines geographical position based on the time it takes to receive signals from three or four separate satellites in orbit around Earth. • Mobile robotic vehicles can use GPS to navigate various terrains or roadways. • Drones use GPS to make sure that they are on target and to give their users information about where they are physically located. Sound • For sound detection, a robotic system needs a microphone, the proper hardware, and the necessary programming so that the robot can turn the signal from the microphone into something useful. • Patterns of sound can be recorded and used as triggers for robot actions. Ultrasonic Sensors • Robots can use ultrasonic sensors to detect or “see” objects via the high-frequency sound that they reflect back. • An ultrasonic sensor is similar to the photo eyes or photoelectric prox switches except that they are emitting and receiving sound instead of light. • The emitter sends out a high-frequency sound pulse, above the human range of hearing, which strikes objects and then returns to the ultrasonic sensor. • The receiver measures the amount of time that it takes the sound wave to return and uses this to calculate the distance. • To determine the distance, take the speed of the sound wave, multiply it by the time it took for the wave to return, and then divide by 2. • Another use for ultrasonic sensors is the detection of air leaks. • Small air leaks emit a high-frequency sound that we cannot hear, but that the ultrasonic detector can pick up with ease. Vision Systems • Allow robots to see the world around them, using cameras and software that processes the images taken by the camera. • Dr. Robert Shillman truly started the odyssey of robotic vision with the DataMan system in 1982. • The modern vision system consists of a specialized light source, a camera mounted on the robot or at a specific point, and specialized software from either the robot or the vision system manufacturer. • The other key point of a modern vision system is determining where the part is by the image. • The basic process is to place a calibration image in a location where the robot can reach, take a picture, and then use the system software to translate that image into point data. • The next step is to take an image of what the parts should look like and use this as a reference image. • During operation, the robot will take a picture of the designated area, compare this to the reference picture, and use the positional data that it was given at calibration to offset motions.