Magnetostrictive force sensors make use of this property to sense the amount of deflection that has occurred in the force sensor as a result of the applied load.
The deflection can then be translated into a value representing the weight of the object or the magnitude of the applied force. Strain gage load cells are ones that make use of a strain gage as the sensing element. The following section explains what strain gages are and how they function. Strain gages also spelled as strain gauges are a type of sensor element whose electrical resistance varies as a result of an applied force. Stress is the term used to describe the internal resistance force that an object will exhibit to the external application of force, while a strain is the measure of the amount of deformation and displacement that the object will experience as a result of the applied external force.
The typical strain gage consists of an insulating substrate onto which a conductive metallic foil pattern has been deposited in a zig-zag pattern. When the strain gage is subjected to a force, the device will either compress or elongate depending on the direction of the applied force.
The elongation or compression of the strain gage distorts the metallic foil pattern on the substrate, which changes its electrical resistance. The change in electrical resistance can be used to measure the applied force to the strain gage. An electrical bridge network known as a Wheatstone bridge circuit is typically used to convert the change in resistance of the strain gage to a voltage measurement.
Force Sensing Resistors FSRs , also known as printed force sensors or force-sensitive resistors, are a type of piezoresistive sensing technology that consists of a semi-conductive material or ink which is sandwiched between two substrates that are separated by a spacer. When a force is applied to the device, a conductive film is deformed and presses against a conductive ink printed on the substrate. As more of the conductive film comes in contact with the printed conductive layer, the resistance of the device decreases.
With zero force applied, the sensor exhibits a very high resistance on the order of Meg-ohms. The resistance drops inversely proportional to the applied force. Since conductance is the inverse of resistance, the FSRs exhibit a linear increase in conductance with increased force. FSRs can be configured for point source detection or used in an array design for detecting force distribution applied over an area pressure.
Two additional force sensor types are optical force sensors and ultrasonic force sensors. Optical force sensors typically employ a fiber optic cable into which has been inscribed a Fiber Bragg Grating FBG at specific intervals along the length of the cable.
When the cable is subjected to stress or strain, the separation distance of the grating changes. By monitoring the reflections from light as it is passed through the cable, the degree of deformation elongation or compression can be established and used to determine the force applied. This same concept is not only used to measure force , but also to measure liquid pressure, flow and is even used in the touch screens on a mobile phone.
Because capacitive sensors use an alternating signal, it means that they are inherently digital. This is a real bonus for robot force sensing because it increases the resistance to noise significantly. Also, it means that we don't have to use an Analog-to-Digital converter, which reduces the required electronics. Just like with the strain gauge Force-Torque Sensors, the two ends of the sensor are attached through a compliant metal element. However, this time it is not in the form of a "metal cartwheel.
This structure is attached to two metal plates one at each end. These plates hold a specially positioned set of capacitive sensors to measure the displacement between them. There are several advantages to using capacitive sensors in FT Sensors over the traditional strain gauges, in addition to their immunity to noise. Capacitive sensors generally produce a stronger output so less signal conditioning is needed, which ultimately means better accuracy.
Also, capacitive sensors don't rely on the adhesive bond between the metal and the strain gauge, meaning that they can withstand millions more force readings without affecting their accuracy. The integrated electronics of a Force-Torque Sensor allow you to easily access the data. Most of the Force-Torque Sensors we use in robotics have integrated electronics, which thankfully means you don't have to do the signal processing yourself.
They also have a variety of different communication options which allow you to easily get the data from the sensor. The integrated electronics convert the multiple sensor readings into six easy to understand signals: Fx, Fy and Fz the forces and Mx, My and Mz the Torques or Moments.
Mathematically, this conversion is often carried out by multiplying the sensor readings with a pre-defined matrix. The matrix is defined by the sensor's manufacturer and are dependent on the material properties of the compliant metal structure. These properties will never change, unless you plastically deform the metal by applying too much force to the sensor.
As you can imagine, it's important to make sure you never apply too much force to the sensor, as the whole of its operation is based around the fact that the metal should never deform plastically.
That's why you should pay attention to the Maximum Overload Capacity when choosing a Force-Torque Sensor for research. However, Maximum Overload Capacity is not the only important specification when choosing a force sensor for your robotics research. There are a whole load of specifications which affect which choice is the best for your application. Once you've decided these specifications, you've got to decide how to apply the sensor to your research and what are the best ways to integrate it into your existing system.
Wouldn't it be great if you had one place you could find all this information? We've developed a free eBook and email series to give you a crash course in using force sensors for robotics research. In it, we cover more detail about how they work, guides to integrating force sensors into your research application, how to use ROS with a force sensor and much more.
Download the eBook by clicking the big button below! Did we mention, it's free! How do you, or how would you like to, use force sensors in your research? Have you downloaded the free eBook? Do you have any questions about force sensors? Tell us in the comments below or join the discussion on LinkedIn , Twitter or Facebook. You have decided to include force sensing in your robot application.
Perhaps your task requires tactile feedback, flexibility, Do you need a force sensor for your chosen robot application? The flexibility of this technology, combined with their operating capabilities, and their ability to function on simple circuitry, make them a great option for embedding into smart devices with limited space and power constraints. FlexiForce sensors are also highly customizable. This article covers several performances differences between shunt and thru mode sensor technologies, including how they compare on linearity, drift, precision, and other key factors.
While new uses for force sensing resistor technology are being discovered every day, most applications tend to fall under four different use categories:. This short video provides more visual context around these different use cases for force sensing resistors — specifically FlexiForce force sensing resistors:. At Tekscan, we offer a range of standard FlexiForce force sensing resistors in low-cost, low-quantity packs, from our online store.
We also offer force measurement systems and OEM proof-of-concept and integration kits to assist you in your diverse force measuring needs. For any other questions on force sensing resistor technology, contact a Tekscan engineer today!
Dental Digital Occlusal Analysis. How are Force Sensing Resistors Made? How are Force Sensing Resistors Used? Post Categories:. To print this web page, please use our "share" tools.
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