The last time you put something along with your hands, whether it was buttoning your shirt or rebuilding your clutch, you used your sense oftouch more than you may think. Advanced measurement tools including gauge blocks, verniers as well as coordinate-measuring machines (CMMs) exist to detect minute differences in dimension, but we instinctively use our fingertips to check if two surfaces are flush. In fact, a 2013 study found that the human sense of touch may even detect Nano-scale wrinkles on an otherwise smooth surface.
Here’s another example through the machining world: the outer lining comparator. It’s a visual tool for analyzing the finish of the surface, however, it’s natural to touch and notice the surface of the part when checking the conclusion. Our minds are wired to make use of the data from not only our eyes but additionally from our finely calibrated torque sensor.
While there are several mechanisms by which forces are converted to electrical signal, the primary areas of a force and torque sensor are similar. Two outer frames, typically manufactured from aluminum or steel, carry the mounting points, typically threaded holes. All axes of measured force may be measured as you frame acting on the other. The frames enclose the sensor mechanisms and any onboard logic for signal encoding.
The most frequent mechanism in six-axis sensors will be the strain gauge. Strain gauges include a thin conductor, typically metal foil, arranged in a specific pattern on a flexible substrate. As a result of properties of electrical resistance, applied mechanical stress deforms the conductor, which makes it longer and thinner. The resulting change in electrical resistance can be measured. These delicate mechanisms can easily be damaged by overloading, as the deformation from the conductor can exceed the elasticity in the material and cause it to break or become permanently deformed, destroying the calibration.
However, this risk is normally protected by the appearance of the sensor device. As the ductility of metal foils once made them the typical material for strain gauges, p-doped silicon has shown to show a significantly higher signal-to-noise ratio. For that reason, semiconductor strain gauges are gaining popularity. As an example, all of triaxial load cell use silicon strain gauge technology.
Strain gauges measure force in a single direction-the force oriented parallel to the paths within the gauge. These long paths are designed to amplify the deformation and thus the modification in electrical resistance. Strain gauges are not sensitive to lateral deformation. For this reason, six-axis sensor designs typically include several gauges, including multiple per axis.
There are a few options to the strain gauge for sensor manufacturers. For example, Robotiq developed a patented capacitive mechanism at the core of their six-axis sensors. The goal of making a new form of sensor mechanism was to produce a method to appraise the data digitally, rather than as an analog signal, and lower noise.
“Our sensor is fully digital without 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 is not really immune to external noise. Comparatively, capacitance tech is fully digital. Our sensor has almost no hysteresis.”
“In our capacitance sensor, the two main frames: one fixed then one movable frame,” Jobin said. “The frames are connected to a deformable component, which we are going to represent as being a spring. Once you use a force to nanzqz movable tool, the spring will deform. The capacitance sensor measures those displacements. Learning the properties in the material, it is possible to translate that into force and torque measurement.”
Given the price of our human feeling of touch to our motor and analytical skills, the immense possibility of advanced touch and force sensing on industrial robots is obvious. Force and torque sensing already is at use in collaborative robotics. Collaborative robots detect collision and may pause or slow their programmed path of motion accordingly. This will make them able to working in contact with humans. However, most of this type of sensing is performed using the feedback current in the motor. Should there be a physical force opposing the rotation in the motor, the feedback current increases. This change could be detected. However, the applied force should not be measured accurately using this method. For more detailed tasks, load cell is required.
Ultimately, industrial robotics is all about efficiency. At trade shows and in vendor showrooms, we see plenty of high-tech bells and whistles designed to make robots smarter and much more capable, but on the financial well being, savvy customers only buy just as much robot as they need.