The final time you put something 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 such as 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. Actually, 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 surface comparator. It’s a visual tool for analyzing the conclusion of a surface, however, it’s natural to touch and notice the surface of your own part when checking the conclusion. The brain are wired to make use of the details from not just our eyes but also from our finely calibrated Micro Load Cell.
While there are several mechanisms by which forces are converted to electrical signal, the main parts of a force and torque sensor are the same. Two outer frames, typically made from aluminum or steel, carry the mounting points, typically threaded holes. All axes of measured force may be measured as one frame acting on another. The frames enclose the sensor mechanisms and any onboard logic for signal encoding.
The most typical mechanism in six-axis sensors will be the strain gauge. Strain gauges contain a thin conductor, typically metal foil, arranged within a specific pattern over a flexible substrate. Due to the properties of electrical resistance, applied mechanical stress deforms the conductor, which makes it longer and thinner. The resulting improvement in electrical resistance can be measured. These delicate mechanisms can be easily damaged by overloading, since the deformation in the conductor can exceed the elasticity in the material and make it break or become permanently deformed, destroying the calibration.
However, this risk is usually protected by the design of the sensor device. Whilst the ductility of metal foils once made them the typical material for strain gauges, p-doped silicon has proven to show a much higher signal-to-noise ratio. Because of this, semiconductor strain gauges are becoming more popular. 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 for the paths inside the gauge. These long paths are designed to amplify the deformation and so the modification 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 made a patented capacitive mechanism in the core of the six-axis sensors. The aim of making a new form of Torque Sensor was to create a way to measure the data digitally, as opposed to being an analog signal, and lower noise.
“Our sensor is fully digital without strain gauge technology,” said JP Jobin, Robotiq vice president of research and development. “The reason we developed this capacitance mechanism is simply because the strain gauge is not really resistant to external noise. Comparatively, capacitance tech is fully digital. Our sensor has virtually no hysteresis.”
“In our capacitance sensor, there are 2 frames: one fixed and one movable frame,” Jobin said. “The frames are attached to a deformable component, which we shall represent as a spring. Whenever you use a force for the 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 value of our human sensation 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 within use in the field of collaborative robotics. Collaborative robots detect collision and will pause or slow their programmed path of motion accordingly. As a result them competent at working in contact with humans. However, much of this type of sensing is carried out using the feedback current from the motor. Should there be an actual force opposing the rotation of the motor, the feedback current increases. This modification could be detected. However, the applied force wbtbtc be measured accurately using this method. For more detailed tasks, Multi Axis Load Cell is required.
Ultimately, industrial robotics is approximately efficiency. At trade shows and then in vendor showrooms, we percieve a lot of high-tech special features made to make robots smarter and more capable, but on the bottom line, savvy customers only buy as much robot as they need.