These days drones seem flying above all. As we are getting dependent directly or indirectly of the tremendous potential of these flying robots— detailed studying and intelligent approach to them will be fundamental. Our main purpose in this article will be discussing the drones sensors in a more detailed manner.
Sensing and actuation systems contain sensors to observe the environment and actuators to influence it. Over all if we see sensors in a broader sense. We need to know more about them not only for they are the main components of drones and other land surveying equipment, but also for they are a crucial component of any intelligent control system in the now a days smart things like smart cities,Smart Environment,Smart Water,Smart Metering,Security & Emergencies,Smart Agriculture,Smart Animal Farming… which means living in a modern society sensors getting to controlling all our daily live situations directly or indirectly—We ordained to know about sensors also even just as being one of a smart city dwellers.
Sensors are devices that detect physical properties in nature and convert them to quantitative values for actuators and control systems. These physical properties can be specific inputs like light, heat, motion, moisture, pressure, or any one of a great number of other environmental phenomena. The output is generally a signal that is converted to human-readable display at the sensor location or transmitted electronically over a network for reading or further processing.
Involvement of Drones in Remote Sensing
Drones are used as platforms to put the different remote sensing sensor systems. Knowing remotesensing is a science which really is fastly growing specially at its last decade of age. The introduction of Drones to remote sensing as a platform is so aggressively invading most areas of the remote sensing. Surprisingly with this simple but relatively cheapest platformed there comes some clear improvements in some aspects as well. For example: Few years a go having orthophoto data maps with as big scale as in today’s drones remote sensing systems providing was almost a dream. Even if it was possible it would not be as cheapest and as easy as we are doing using drones today. This trend forecasts already what it will be liked the future’s relationship between all the geo professionals and the drones—Which is our only driving factor to focus mainly in to get to know more about this flying machines.
Drone sensors by we mean here is sensors in drone’s body—the sensor systems that make up the drone itself. Drone sensors can generally classified as proprioceptive, exteroceptive, exproprioseptive sensors. Sensors classifications of drone— that will be an article coming soon. But first,
Sensors in the Drone’s Body
In today’s fast growing drone market, sensor technologies are often the overlooked secret sauce inside. Some people may think it is quite technical to discuss about these bodies. However since we believe that even a little knowledge about drone’s sensors helps us to approach, communicate and to use our drones accordingly we prefer to take up the issue here as follows.
fig 1 the main internal body components as shown schematically (taken from Wikipedia)
The above schematic figure shows us the main components of a UAV and their connection. As we can see from the schematic figure the Sensors showed as one of the main internal body part of a drone. We see modern drones incorporating many sensors every year to in-power them to more and more autonomous. However We believe that we gonna discuss about the main drone’s Sensors like Accelerometer, Gyroscopes, Inertial Measurement Units (IMU), Compass/Magnetometer, Pressure/Barometer, GPS and distance sensors in a more detailed manner.
Accelerometers are used to determine position and orientation of the drone in flight. These small usually silicon-based sensors play a key role in maintaining flight control. While it’s most common applications are: in tilt sensors in static application, in Vibration analysis, and to fulfil the INS system.
Accelerometers measure(returns signal proportional to… ) acceleration forces. These forces may be as static as the constant force of gravity pulling any object downward, or they could be dynamic – caused by moving or vibrating the accelerometer.
There are many types of accelerometers developed and reported in the literature. The vast majority is based on piezoelectric crystals, but because of they are not so compacted and too big People attempted to develop something smaller, that could increase applicability and started searching in the field of microelectronics. In this endeavor MEMS (micro electromechanical systems) accelerometers are developed. [Researches indicate that MEMS can be manufactured in Silicon, in polymer, in glass, in quartz or even in metals].
illustrating the concept
Accelerometer can measure(returns signal proportional to… ) acceleration indirectly from measuring change in capacitance. It has a mass attached to a spring which is confined to move along one direction and a fixed outer plates. When an acceleration in a particular direction will be applied, the mass will move and the capacitance between the plates and the mass will change. And then this change in capacitance will be measured processed and it will corresponded to a particular acceleration.
The majority of microelectromechanical system (MEMS) devices must be combined with integrated circuits (ICs) for operation in larger electronic systems. While MEMS transducers sense or control physical, optical or chemical quantities, ICs typically provide functionalities related to the signals of these transducers, such as analog-to-digital conversion of the capacitance in the accelerometers.
MEMS Accelerometers (Accelerometer ICs)
Fig.2 shows the microscopic wafer structure of MEMS
The term used to define micro electro-mechanical systems (MEMS) varies in different parts of the world. In the United States they are predominantly called MEMS, while in some other parts of the world they are called “Microsystems Technology” or “micromachined devices”. There critical physical dimensions can vary from well below one micron on the lower end of the dimensional spectrum, all the way to several millimeters. Where as there types can vary from relatively simple structures having no moving elements, to extremely complex electromechanical systems with multiple moving elements under the control of integrated microelectronics.
MEMS became practical once they could be fabricated using modified semiconductor device fabrication technologies, normally used to make electronics. These include molding and plating, wet etching (KOH, TMAH) and dry etching (RIE and DRIE), electro discharge machining (EDM), and other technologies capable of manufacturing small devices.
Simply MEMS is a state of the art technology currently micro things like microsensors, microactuators, Microelectronics…can be manufactured. Microsensors and microactuators are appropriately categorized as “transducers”, which are defined as devices that convert energy from one form to another. Microsensors helps typically to converts a measured mechanical signal into an electrical signal.
While proof of mass, Suspension mechanism, and Sensing element are the main elements of an accelerometer there are also others like: plate, hinge, restrictor, pyramid, pad, flexure, capacitance fingers and several components that interact with the surroundings such as microsensors. Inside each accelerometer devices there are microscopic mechanical elements that move along with the external forces caused by movement or rotation. These forces spread out further more into numerous components.
Fig. 3 showing the capacitance mimic motion of MEMS one direction Sensor tech.
In MEMS accelerometers or Accelerometer ICs under the influence of external accelerations the proof mass deflects from its neutral position. This deflection is measured in an analog or digital manner. Most commonly, the capacitance between a set of fixed beams and a set of beams attached to the proof mass is measured. An integrated electronic evaluates the capacity changes and allows conclusions to the occurring accelerations. This method is simple, reliable, and inexpensive.
Integrating piezoresistors in the springs to detect spring deformation, and thus deflection, is a good alternative, although a few more process steps are needed during the fabrication sequence. In piezoelectric accelerometers— MEMS accelerometer apply mainly as tilt and orientation sensor. Here, the electric signal generated from the Piezoresistive patch and the bulk device due to vibration is proportional to the acceleration of the vibrating object.
A compromise between sensitivity and the maximum acceleration that can be measured are the challenges in the designing and manufacturing process of MEMS.
MEMS Gyroscopes (gyroscopes manufactured with MEMS technology)
In normal situation a gyroscope measures(returns signal proportional to… ) changes in tilt, orientation, and rotation based on angular momentum. These are inertial sensors on your drone which can measure the rotation rate of an object around one linear axis of (X-Y-Z). For each axis we have one gyroscope or even one gyroscope for two axes even there can be a gyroscope for the three axes depends on the design. That’s telling you how fast is the drone rotating along the axis—if you are not rotating zero rotating (a position of stability).
tHE MEMS Gyro’s PURPOSE AND MEANING:
To make the flight control modules of drones small, lightweight, and inexpensive, Micro-Electro-Mechanical Systems (MEMS) gyroscopes are used. It is thus a core sensor for flight attitude control and position balancing. The gyros we are talking about here are a rate Gyro types—They cannot determine the angular velocity unlike the normal Gyros do. Remember that in our [The drones computing body] section we also discussed MEMS gyroscopes doesn’t know what your pitch is but it knows your rate of pitch. When you put the drone on the ground and plug it in— it takes that position-value as a zero value… The main purpose of gyroscopes here is in measuring angular motion as a form of angular acceleration about one or several axis as an input to control a system. This measurement value is used as an input in the drones computing body to compute the drones instability compensations.
understanding mems GYROS:
To understand the role of gyro stabilization, it’s important to realize that every drone is constantly being subjected to a number of forces coming from different directions. These forces, such as wind, affect drone’s yaw, pitch, and roll, thus, potentially, making the drone very hard to control.
HOW MEMS GYROS WORK
MEMS gyroscopes can almost instantly detect changes in the position of a drone and the flight controller calculates the compensate for it in such a way that it basically seems unaffected as this procedure done hundreds of time every second or can hover calmly in place. Modern gyroscopes are manufactured with components between 1 to 100 micrometers in size and often include sensors for multiple axes in a single package.
These are packaged similarly to other integrated circuits and may provide either analog or digital outputs. Although a good accelerometer can do a reasonable job of this unless it’s in free fall as well. They usually shown up alongside accelerometers to improve input speed and accuracy.
More About Accelerometers
In many cases, a single part includes gyroscopic sensors for multiple axes. Some parts incorporate multiple gyroscopes and accelerometers (or multiple-axis gyroscopes and accelerometers), to achieve output that has six full degrees of freedom. These units are called inertial measurement units, or IMUs.
Mems accelerometers Their nature of design
Most MEMS accelerometers operate in-plane, that is, they are designed to be sensitive only to a direction in the plane of the die. By integrating two devices perpendicularly on a single die a two-axis accelerometer can be made. By adding another out-of-plane device three axes can be measured. Such a combination may have much lower misalignment error than three discrete models combined after packaging.
Thermal MEMS Sensors For VideoFilming
By controlling up and down movement, as well as removing jitter and vibration, filmmakers are able to capture extremely smooth looking video. Additionally, because these sensors are more immune to vibrations than other technologies, thermal MEMS sensors are perfect in drone applications to minimize problems from the increased vibration generated by the movement of rotating propulsion fans and propellers.
Inertial Measurement Units
Inertial measurement units combined with GPS gives us (INS—Inertial Navigation Systems) are critical for maintaining direction and flight paths. As drones become more autonomous, these are essential to maintain adherence to flight rules and air traffic control. Please read our [INS—Inertial Navigation Systems page] for a simpler conceptual understanding.
Inertial measurement units also utilize multi-axis magnetometers that are in essence small, accurate compasses. These sense changes in direction and feed data into a central processor, which ultimately indicates direction, orientation, and speed.
In drones, power consumption and use are important for autopilot to receive a clean power supply. Current sensors can be used to convert the battery voltage from your drone battery down to a as low voltage as your drone can can use, monitor and optimize power drain, safe charging of internal batteries, and detect fault conditions with motors or other areas of the system.
Current sensors work by measuring electrical current (bi-directional) and ideally provide electrical isolation to reduce power loss and eliminate the opportunity for electrical shock or damage to the user or systems. Sensors with fast response time and high accuracy optimize battery life and performance of drones.
Quad-Constellations—GPS, GALILEO, BeiDou, GLONASS,…
This one is is a mechanism for determining the location of an object in space. Technologies for this task exist ranging from worldwide coverage with meter accuracy to workspace coverage with sub-millimetre accuracy. it provides aircrafts geographical position, as well as speed and absolute altitude (ASL). It is required for almost any autonomous flight mode like mission, return to home, as well as position hold. There is enough in the internet on the topic, so to keep thing short:
Magnetometers are sensors that you sometimes see in a UAV stabilization systems. We may frequently see them in the high end units rather than in the lower end units.
Magnetometer measures the angles with reference to magnetic north. An electronic magnetic compass is able to measure the earth’s magnetic field and used it to determine the drone‘s compass direction (with respect to magnetic north). This sensor is almost always present if the system has GPS input and is available in one to three axes. Therefore it is a good unit to correct some direction drifts that may happen due to some systematic errors. There cones part is that they easily affected by any magnetic fields or steel materials on the way. Which can introduce a potential error for the system even though there is a way of calibration to minimize error introduced due to these cases.
However currently there are some magnetometer technology sensors out there, which have superior accuracy and response time characteristics while consuming significantly less power, which are well-suited to drone applications. These prov
ide drone manufacturers with quality data sensing in a very rugged and compact package.
A tilt sensor can measure the tilting in often two axes of a reference plane. In contrast, a full motion would use at least three axes and often additional sensors. One way to measure tilt angle with reference to the earths ground plane, is to use an accelerometer.
Tilt sensors, combined with gyros and accelerometers, provide input to the flight-control system in order to maintain level flight. This is extremely important to do tasks with drones where stability is preeminent, like orthofoto production.
These types of sensors usually combine accelerometers with gyroscopes to allowing the detection of even small variations in movement. Because the gyroscope compensates the drift these tilt sensors to be used in moving applications like motor vehicles or drones.
Mass Flow Sensors
A mass (air) flow sensor (MAF) is used to find out the mass flowrate of air entering a fuel-injected internal combustion engine used to power some drone varieties. These help the engine control unit (ECU) determine the proper fuel-to-air ratio at a specified engine speed, which results in improved power and efficiency, and reduced emissions.
Many gas engine mass-flow sensors employ a calorimetric principal utilizing a heated element and at least one temperature sensor to quantify mass flow. MEMS thermal mass air flow sensors also utilize the calorimetric principal, but in a micro scale, making it highly suitable for applications where reduced weight is critical.
What are Pressure Sensors?
Barometer measures air pressure. A pressure sensor is a device that senses pressure and converts it into an electric signal where the amount depends upon the pressure applied.
The principle here is atmospheric pressure changes the farther away you are from sea level, then a pressure sensor is employed to give you a pretty accurate reading for the UAV’s height. Most flight controllers take input from both the pressure sensor and GPS altitude to calculate a more accurate height above sea level. Note that it is preferable to have the barometer covered with a piece of foam to diminish the effects of wind over the chip.
Pressure sensors can be classified in terms of pressure ranges they measure, temperature ranges of operation, and most importantly the type of pressure they measure. Pressure sensors are variously named according to their purpose, but the same technology may be used under different names. Evidently the main applications of pressure sensors in Aircraft’s body of all sorts can be :
- Pressure sensing : While some drones have been developed and sold with ultrasonic sensors, pressure sensors improve the hovering mode of the most basic drones.
- Altitude sensing: Since pressure drops with altitude, Pressure sensors can be used to measure altitude as well.
Usually these types of sensors are able to determine the pressure applied to gas or liquids. Some of the types of pressure sensors in use include gauge pressure sensors and vacuum pressure sensors. Aircraft of all sorts have different applications for pressure sensing. Drones in particular employ altimeters and barometers similar to even the most and least sophisticated aircraft.
The figure above shows Barometer as shown at the bottom of a flight controller
These are sensors being used more and more on drones since GPS coordinates and pressure sensors alone cannot tell you how far away from the ground (thick hill, mountain or any object) you are or if you will hit an object. Their task is measuring the distance between an unmanned aerial vehicle and an object, without physical contact of the object. A downward-facing distance sensor might be based on ultrasonic, laser or LiDar technology (infrared has issues in sunlight). Very few flight controllers include distance sensors as part of the standard package.
These are all the main sensors that we frequently hear about or we use in the drones world and we thought have to be covered in this literature. Honestly, we are not aerospace engineers we know about this challenging areas through reading and learning from some scientific papers and articles on different websites and other types of paper written resources but mainly we take Wikipedia as our main resource to make the this and other article remember that even-though we did all our possible efforts to avoid the conceptual errors there might be some errors possibly. where we believe that this article can give the beginners having at least a mind picture reference, which can strike interest and encouragements to dig more about the area. Please help us to improve ourselves by leaving your comments about the article just below the article inside the comment box. Let us know if you have any questions or want any clarification on any of these Sensors types or anyone else of drones sensors out there and we will try our best to help you out!