robotics ch 7

what is the typical sequence for photoelectric switch operation?

1. An oscillator module turns the transmitter, usually an infrared LED, on and off at high speeds 2. The light either travels in a straight line to the receiver or is reflected by some surface 3. the receiver, when the correct light strikes it, transmit signals to the internal components of the switch 4. if a threshold is met, the switch changes the state of contacts or passes along information into another process. This threshold value is adjustable in many sensors, and the adjustment is crucial for small, fast moving parts. 5. if the wrong frequency or type of light enters the receiver or if not enough of the transmitted light makes it to the receiver, the switch does not change conditions or passes on other partial information

What are the three main things to verify when making a sensor connection to the robot?

1. Make sure it is the right type of voltage, AC or DC. 2. make sure it is the right level of voltage, as too much can cause damage and too little will likely not trigger the input or run the output. 3. make sure it is the right type, digital (on and off) or analog (a range). When the signal is analog, make sure it is the right type of signal for the card it is tide two and the device it works with.

What are the six main criteria for selecting a sensor?

1. What are you measuring 2. operating environments 3. fail safe requirements 4. accuracy 5. type of output 6. cost versus performance

What is the sensing range for inductive proximity switches from low power to high power?

A common range for DC prox switches is 10-30 volts; a common range for AC prox switches is 20-264 volts. Some prox switches can work on either AC or DC voltage, in which case this common range is 24-240 volts.

what can we use light level photoelectric prox switchs to detect?

A light level detection prox could differentiate between a rough, raw part and a smooth, finished part as it passes by based on the differences in the light returned to the switch. we can use this type of procs to make sure labels are in place, monitor empty spots on the conveyor, or detect any other condition where there is a clear and consistent difference in light return to the prox between the two states monitored.

How does an absolute encoder work?

Absolute optical encoders add enough admit errors and receivers, usually four or more in total, to give each position of the encoder its own unique binary address

How can we determine the direction of rotation with incremental encoders?

By adding a second row of reflectors or light windows, offset from the pulse count, and another admitter and receiver, we can determine the direction of rotation by comparing the signals from the two rings.

Describe the operation of a capacitive prox switch

Capacitive proximity switches generate an electrostatic field and work on the same principle as regular capacitors. the switch provides the electromagnetic field, air is the insulating material or the dielectric, and the object being sensed provides the conductor that finishes the capacitive circuit.

What are the parts of the optical encoder? How does this device work?

Consists of a disc that has either holes for the light to pass through or special reflectors to return light, and it matter, a receiver, and some solid state device for signal interpretation and transmission. the principle of operation is simple: 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 to the controller.

how does a hall effect sensor work?

Hall-effect sensors respond to magnetic fields and can produce either a digital on/off type signal or varying analog signal, depending on the sensor and application.

Describe the operation of an inductive prox switch?

Inductive proximity switch uses an oscillating magnetic field to detect ferrous metal items. An oscillating Field goes on and off, in this case, and it creates a wave that looks just like the sine wave of AC voltage.

What are some of the disadvantages of solid-state devices?

Most solid-state devices never fully stopped the flow of electrons, although often only a very small amount leaks through. They are also vulnerable to electromagnetic pulses and other strong magnetic fields

What is the difference between an open loop control system and a closed loop control system?

Open loop systems work on the assumption that the control pulse--whatever it may be--activates the motion system and the robot performs as expected. closed loop systems send out the control pulse--whatever it may be--to initiate movement; they can receive a signal back that confirms movement and sometimes identifies the direction and distance of that movement.

What is the difference between a plunger and a Bourdon tube pressure gauge?

Plunger pressure gauges use a plunger that is exposed to system pressure, a bias spring, a pointer, and a calibrated scale to measure pressure. Bourdon tube gauges uses a thin walled, slightly elliptical, cross-section tube bent in a C shape, which is tied directly to the system, to read pressure

If you have a limit switch in the field that has the actuator in the wrong position and a removable head unit, how would you correct this situation?

There is a feature on this type of limit switch and it has the ability to rotate the head unit of the switch by removing the appropriate screws and then turning the actuator as needed, thereby adapting the switch to the various situations in the field without needing a separate switch to handle each mounting situation

what are the differences between thermocouples, RDT's, and thermostats?

Thermocouples are temperature sensors that work off the principle of a small DC milli voltage generated when the junction of two dissimilar Metals is heated. resistance temperature detectors are based on the principle of a linear increase in resistance that occurs when a metal is exposed to heat. thermostats are resistors that experience a consistent change and resistance with a change in temperature

What is the benefit of disengaging the axes as opposed to the e-stop method of stopping the robot when impact is detected?

This method reduces the force the robot has to stop, the energy of the impact, and the stress on the robot's internal systems

Briefly describe how through beam, reflective, and diffuse photoelectron switches operate.

Through-beam photoelectric sensors separate the transmitter and the receiver into different units, placed opposite each other. Retro reflective photoelectric sensors place the transmitter and the receiver in one assembly, and often use something like a bicycle reflector to return the emitted light to the receiver. diffuse photoelectric sensors also house both transmitter and receiver in one unit, but in this case only a small amount of return light is needed to activate the sensor.

How do we commonly monitor impact today?

Today we typically either monitor the amperage the motor uses or insert sensing devices designed to detect impact

what are the differences between turbine, target, add magnetic flowmeters?

Turbine flowmeters use a propeller or turbine-type assembly placed inside the fluid to generate a signal via a magnetic pickup sensor positioned nearby, but outside of the fluid. target flowmeters place a disk or similar shape in the fluid and use the force of the fluid flow to deflect the target and generate a signal. magnetic flowmeters also known as induction flowmeters, measure the change in voltage induced in the passing fluid.

How do ultrasonic sensors work? How do we determine the distance from the sensor to the object detected?

Ultrasonic sensors are similar to the photo eyes or photoelectric proc switch, except that they admit and receive sound instead of light. An ultrasonic sensor consists of a transceiver, a comparator, it detector, and an output device. The transceiver sends and receives the ultrasonic signal. Because it is both a sender and receiver, it has a dead zone located within a few millimeters of the transducer. signals are sent out in precisely measured pulses at precisely measured intervals, and if a signal should happen to return to the sensor while it is transmitting, the receiver will not detect it. The distance that the dead zone extends from the front of the receiver is determined by the frequency of the signal and the width of the transmitted pulse.

Which information can we gain from a tactile array that senses one or zero?

With this type of sensor, the system knows if it is gripping the part and how many elements are involved with that grip, which is enough to find edges and determine whether the part is moving in the gripper during travel by monitoring for a change in element.

Describe the typical operation of three-probe capacitive level sensor.

With three or more probes are used in capacitive level sensor and, one probe is longer than the rest, and serve as the main electrostatic source. The next longest probe is the low level probe, as soon as the liquid makes contact with this probe, current flows in the sensor. If this is the only probe active in the sensor or if none of the probes is active, then the system knows the fluid is low.. The third probe the shortest of the three, is the high level probe when current flows through this probe, the system knows the fluid has reached the high level and it is time to stop the flow.

What do you need to know 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 is generated by the contacting object.

What is the difference between a sourcing signal and a sinking signal?

a source signal input provides the position connection or DC voltage to the input module. A sinking signal input provides the negative connection or ground to the input module.

Which kinds of information can a high end, complex tactile sensor provide to a robot?

can provide information about the shape of the object, the amount or pressure applied, temperature, finish, and other analog type sensing data that is difficult, if not impossible, to convey with digital signals

Which type of information are we looking for with tactile sensors?

determine how much force is being applied, what the shape of the part is, how it is gripped, and whether the part is hot or cold.

What is optical isolation?

elliptical isolation works by creating a dead zone where the only connection between the internal electronics and the outside connectors is light