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Sensors and Robotics

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Nicole Drevlow

on 12 October 2013

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Transcript of Sensors and Robotics

Sensors and Robotics
What is a sensor?
A sensor is a device that takes some type of information from the physical environment and turns it into an electronic signal.
This information is the input of the sensor and the output is the electronic signal.
The electronic signal is usually either visible in a human language or a signal that an electronic instrument can read.
Pictured here are two thermocouple sensors. They are used to measure extremely high temperatures.
You can see where the electronic wires are on the sensors. This is where the data about the temperature is transferred to another device, such as something used to display the temperature on a screen.
Sensors can measure a variety of things. Temperatures, pressure, audio, distance, light, infrared, and moisture are all things that sensors can measure.
What do sensors measure?
Sometimes sensors are called transducers; however, transducer is a term that refers to any device that converts one form of energy to another form.
Sensors must not have impact their environment; if they did, this would affect the reading of the sensor.
A sensor must be:
Affected only by what it is measuring
Unaffected by other factors in the environment. Example: a heat sensor should not be affected by pressure.
Not capable of affecting what they are measuring.
Types of Sensors
You can classify sensors in a few different ways, but they can usually be divided into the categories of:
Temperature
Pressure
Flow
Biosensors

Image
Chemical
Acceleration
Level sensors

Temperature
Some sensors that deal with temperature are thermistors, thermocouples, RTDs (Resistance thermometer), and IC (Integrated circuit) sensors.
A thermistor is a resistor; it is made so that the amount of resistance changes with temperature. To the right is the icon for a thermistor.
Thermistors are used to stop fuses from blowing, limiting current, temperature sensors, and heat elements that regulate themselves.
Resistance thermometers are similar to thermistors, but resistance thermometers use different materials.
Resistance thermometers are made of pure metal; thermistors are made of polymer or ceramic materials.
Thermocouples are sensors that read temperature by using two pieces of metal that are connected on one end. When the two pieces connect, this creates a voltage that it uses to find the temperature.
Pressure
Pressure sensors include manometers, vacuum gauges, and LVDTs (Linear Variable Differential Transformer).
There are also different ways to measure pressure. Absolute pressure is referenced with a "perfect vacuum." This is the gauge pressure added to atmospheric pressure.
Gauge pressure, mentioned above, is referenced to air pressure, so it is equal to the atmospheric pressure.
Lastly, Differential Pressure is the difference between two pressure points.
Manometers are pressure sensors that use a column of liquid to obtain their reading. They are also called Elastic Liquid Based Manometers.
LVDT sensors themselves do not work with pressure; they measure displacement. However, they are capable of working in high pressure environments without affecting readings.
Flow
Sensors that measure flow can be under different categories, such as electromagnetic sensors, differential sensors, and thermal mass sensors.
Thermocouples don't measure absolute temperature; they measure the difference between two points.
A thermistor is located in the white section above; its purpose is to measure the input temperature.
This regulates the temperature between the large pads pictured in the temperature gauge above.
Sensors can be analog or digital. Digital sensors are simply able to transmit data over a digital medium.
Some analog sensors are still used, but the majority of sensors today are digital. There are analog-to-digital converters that you can use.
These converters will usually work in units of voltage (from the analog input) and convert to a digital measurement, such as numbers that represent the voltage.
Pictured to the left is an analog-to-digital converter used in a stereo. Its location is on the sound card.
Flow in this case refers to the rate at which fluid moves through an area. Sensors that measure flow have to be very precise.
Differential pressure sensors, in short, measure the difference in pressure of the moving water. It will display the rate of flow calculated by the difference in pressure.
Electromagnetic sensors are used to measure flow by using magnetic fields. This creates a difference that is directly related to the force of the flow.
You can use this type of sensor when you have a fluid that can hold ions and a pipe that is conductive, such as a metal pipe lined with rubber.
Biosensors
Biosensors are used to sense things that combine chemistry and biology.
An example of a biological sensor being used in a device is in a blood glucose meter. This meter takes a blood sample and reduces it to a concentration of Glucose. From there, it is able to display how much glucose is in the blood.
Different biosensors can be used for different things.
Surface Plasmon Resonance (SPR) sensors are used in laboratories to observe how reations occur in liquids. It does so by shining a beam of light through the liquid and bounces off of a gold plate.
Image
Image sensors are used to convert light into a type of electrical signal. They are commonly used in cameras and video cameras. Old analog image sensors were made from video camera tubes.
A video camera tube
Modern image sensors use CMOS technology: CMOS stands for Complementary Metal-Oxide Semiconductor.
CMOS sensors are constructed similar to how microprocessors are made. This makes CMOS chips low power consumers, easy to manufacture, have a low cost, and more sensitive to light.
Chemical
Sensors can be used to detect chemicals and chemical balances in different solutions. Some sensors that do this include Semiconductors and Conductivity sensors.
An example of a Semiconductor that measures chemicals is an electrolyte insulator semiconductor. It measures chemical changes between electrolytes.
Conductivity sensors can be used to measure chemical balances, monitoring water levels, and keeping water the purest that it can be. In water it can measure mineral levels, salts, and impurities.
A conductivity sensor is used in this electric conductivity meter.
These meters are used in watching water levels in hydroponic systems, freshwater habitats (such as if you were raising fish), and for plant growing.
Acceleration
Acceleration sensors measure just that: acceleration. Two common sensors of this type are accelerometers and gyroscopes.
Accelerometers measure the forces of acceleration that are exerted on an object. Being able to sense acceleration can help sense other things such as tilt, gravity, collision, and vibration.
Accelerometers measure acceleration in "g"s, referring to g-forces exerted on objects.
Gyroscopes are sensors used to sense the orientation of an object (which includes tilt, which accelerometers can help with).
Here is a gyroscope rendered in three dimensions.
Level Sensors
Level sensors, or fluid level sensors, measure the amount of fluid (the level) in a system.
Level sensors are used in a lot of different ways, such as with gasoline indicators in vehicles, coolant levels in nuclear plants, water levels in fridges, and much more.
Some types of sensors that are used for this task include differential pressure sensors, radar, thermal displacement sensors, capacitors, and magnetoresistance sensors.
The sensors above are capacitors. They use radio technology to sense liquids and gunpowder levels.
This is a magnetoresistance sensor. It uses a magnetic field and angle measurements to find levels.
Tactile Sensors
Tactile sensors are used to sense pressure, forces, and touch. They are used when an object comes in contact with things in the environment.
Touch sensors can be mechanically based or resistance based. Mechanically based sensors operate by essentially toggling a binary switch.
Resistance based sensors operate by measuring the resistance between two points; the surface is temporarily "dented" and the resistance is measured from that dent.
Pressure sensors are basically arrays made of tactels. The world tactel is a shorted form of "tactile element." These tactile elements detect pressure.
Tactels are very effective because of their high number; each tactel on a pressure sensor can be compared to a pixel in an image.
Therefore, tactels produce an image of the pressure exerted on the sensor.
These types of sensors are extremely useful in robotics. They allow you to get more precise results when using robots that require this level of specificity.
A recent development in robotics that included tactile sensors was made by Boston Dynamics. Their newest project, the WildCat, uses a variety of tactile sensors.
The WildCat is able to gallop and bound at 16 miles an hour. It's run by gas engine and is able to respond to what surface it's on by using tactile sensors. It can also navigate rough terrain.
Boston Dynamics has posted a video of "WildCat's best performance so far," according to them.
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Infrared Sensors
To understand Infrared sensors, you need to understand what infrared light is.
Infrared light is light that has a wavelength that is longer than red light.
Infrared sensors are able to read this wavelength and interpret as electric current.
IR sensors can be used in robotics for a few different things. They can be used to sense distance, which you can use to follow lines, avoid obstacles in the robot's path, and for "building" the environment for the robot to reference.
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There are also two kinds of IR sensors: active and passive. They are similar, but serve different purposes.
Active IR sensors emit the source of infrared light and read the reflected light. Passive IR sensors are only able to read infrared light.
Since passive sensors only detect IR, they are useful in sensing the temperature of people and animals. Because passive IR sensors can track this heat, they are able to track motion.
To the left you can see an image of a person rendered using IR sensor data.
Passive IR sensors are also used in home security; they sense movement, so they are able to sense intruders and set off an alarm.
Active IR Sensors
Due to their ability to emit their own light, active IR sensors can be used in night vision applications. This would greatly help a robot that needed to operate in all hours of the day.
To the left is night vision technology powered by an active IR sensor.
Other applications for IR sensors include: hyperspectral imaging, tracking, and communications.
Hyperspectral imaging involves using IR sensors to map out the environment using the electromagnetic spectrum.
This image was rendered using hyperspectral imaging.
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