The last time you put something along with your hands, whether it was buttoning your shirt or rebuilding your clutch, you used your sense of touch a lot more than you may think. Advanced measurement tools including gauge blocks, verniers and even coordinate-measuring machines (CMMs) exist to detect minute variations in dimension, but we instinctively use our fingertips to ascertain if two surfaces are flush. In reality, a 2013 study found that the human sense of touch can even detect Nano-scale wrinkles on an otherwise smooth surface.
Here’s another example from the machining world: the surface comparator. It’s a visual tool for analyzing the finish of any surface, however, it’s natural to touch and feel the surface of your own part when checking the finish. Our brains are wired to use the information from not just our eyes but in addition from the finely calibrated Compression Load Cell.
While there are numerous mechanisms through which forces are changed into electrical signal, the main elements of a force and torque sensor are the same. Two outer frames, typically manufactured from aluminum or steel, carry the mounting points, typically threaded holes. All axes of measured force can be measured as one frame working on another. The frames enclose the sensor mechanisms as well as any onboard logic for signal encoding.
The most common mechanism in six-axis sensors is the strain gauge. Strain gauges contain a thin conductor, typically metal foil, arranged in a specific pattern on a flexible substrate. Because of the properties of electrical resistance, applied mechanical stress deforms the conductor, making it longer and thinner. The resulting change in electrical resistance could be measured. These delicate mechanisms can easily be damaged by overloading, as the deformation in the conductor can exceed the elasticity from the material and make it break or become permanently deformed, destroying the calibration.
However, this risk is normally protected through the design in the sensor device. As the ductility of metal foils once made them the typical material for strain gauges, p-doped silicon has seen to show a much higher signal-to-noise ratio. For that reason, semiconductor strain gauges are gaining popularity. For instance, most of ATI Industrial Automation’s six-axis sensors use silicon strain gauge technology.
Strain gauges measure force in one direction-the force oriented parallel to the paths within the gauge. These long paths are created to amplify the deformation and so the alteration in electrical resistance. Strain gauges usually are not sensitive to lateral deformation. For this reason, six-axis sensor designs typically include several gauges, including multiple per axis.
There are some alternatives to the strain gauge for sensor manufacturers. For example, Robotiq developed a patented capacitive mechanism in the core of their six-axis sensors. The goal of creating a new form of Rotary Torque Sensor was to create a method to look at the data digitally, as opposed to as an analog signal, and lower noise.
“Our sensor is fully digital with no strain gauge technology,” said JP Jobin, Robotiq v . p . of research and development. “The reason we developed this capacitance mechanism is because the strain gauge will not be safe from external noise. Comparatively, capacitance tech is fully digital. Our sensor has almost no hysteresis.”
“In our capacitance sensor, there are two frames: one fixed and one movable frame,” Jobin said. “The frames are attached to a deformable component, which we will represent being a spring. When you use a force towards the movable tool, the spring will deform. The capacitance sensor measures those displacements. Understanding the properties in the material, you are able to translate that into force and torque measurement.”
Given the need for our human sense of touch to our own motor and analytical skills, the immense potential for advanced touch and force sensing on industrial robots is obvious. Force and torque sensing already is at use in the area of collaborative robotics. Collaborative robots detect collision and may pause or slow their programmed path of motion accordingly. As a result them able to doing work in contact with humans. However, a lot of this sort of sensing is performed through the feedback current from the motor. If you have a physical force opposing the rotation from the motor, the feedback current increases. This modification can be detected. However, the applied force wbtbtc be measured accurately by using this method. For additional detailed tasks, 3 Axis Load Cell is required.
Ultimately, industrial robotics is all about efficiency. At trade shows as well as in vendor showrooms, we percieve plenty of high-tech special features made to make robots smarter and more capable, but on the bottom line, savvy customers only buy the maximum amount of robot as they need.