The very last time you put something together with your hands, whether or not 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 and even coordinate-measuring machines (CMMs) exist to detect minute variations 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 can even detect Nano-scale wrinkles on an otherwise smooth surface.
Here’s another example from your machining world: the surface comparator. It’s a visual tool for analyzing the finish of the surface, however, it’s natural to touch and experience the surface of the part when checking the conclusion. Our brains are wired to use the details from not merely our eyes but in addition from our finely calibrated rotary torque sensor.
While there are numerous mechanisms through which forces are converted to electrical signal, the key parts 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 could be measured as you frame acting on the other. The frames enclose the sensor mechanisms and any onboard logic for signal encoding.
The most common mechanism in six-axis sensors is the strain gauge. Strain gauges include a thin conductor, typically metal foil, arranged in a specific pattern over a flexible substrate. Because of the properties of electrical resistance, applied mechanical stress deforms the conductor, rendering it longer and thinner. The resulting improvement in electrical resistance may be measured. These delicate mechanisms can be easily damaged by overloading, as the deformation of 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 style of the sensor device. As the ductility of metal foils once made them the typical material for strain gauges, p-doped silicon has proven to show a significantly higher signal-to-noise ratio. Because of this, semiconductor strain gauges are becoming more popular. For instance, all 3 axis load cell use silicon strain gauge technology.
Strain gauges measure force in a single direction-the force oriented parallel towards the paths inside the gauge. These long paths are made to amplify the deformation and thus the modification in electrical resistance. Strain gauges are not sensitive to lateral deformation. Because of this, six-axis sensor designs typically include several gauges, including multiple per axis.
There are several options to the strain gauge for sensor manufacturers. For instance, Robotiq developed a patented capacitive mechanism in the core of its six-axis sensors. The objective of making a new type of sensor mechanism was to make a method to appraise the data digitally, instead of as 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 because the strain gauge will not be resistant to external noise. Comparatively, capacitance tech is fully digital. Our sensor has hardly any hysteresis.”
“In our capacitance sensor, there are two frames: one fixed then one movable frame,” Jobin said. “The frames are connected to a deformable component, which we will represent as a spring. Once you use a force to nanzqz movable tool, the spring will deform. The capacitance sensor measures those displacements. Understanding the properties of the material, you can translate that into force and torque measurement.”
Given the price of our human feeling of touch to the motor and analytical skills, the immense prospect 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 capable of working in contact with humans. However, much of this sort of sensing is performed using the feedback current of the motor. Should there be an actual force opposing the rotation from the motor, the feedback current increases. This transformation can be detected. However, the applied force can not be measured accurately using this method. For more detailed tasks, compression load cell is required.
Ultimately, industrial robotics is all about efficiency. At trade events as well as in vendor showrooms, we see plenty of high-tech features made to make robots smarter and much more capable, but on the bottom line, savvy customers only buy as much robot as they need.