A Gradiometric Magnetic Force Sensor Immune to Stray Magnetic Fields for Robotic Hands and Grippers

Abstract

To enable precise manipulation of fragile objects, robots need the sense of touch. Localized sensing of the 3D force vector with a few mN of resolution is desired. Magnetic force sensors, consisting of a magnet embedded in an elastomer and a 3D magnetometer, were demonstrated as desirable candidates. These prior-art sensors measure the local 3D magnetic field at a single sensing pixel. Hence, they cannot distinguish between the signal and stray magnetic fields. Any stray field directly leaks into the force readout signal path. This paper introduces a design immune to stray magnetic fields. The sensor uses multiple magnetic pixels, and operates on the gradient of the magnetic field. The pixels and conditioning electronics are fully integrated on chip. The 3D force calculation is based on a polynomial model fitted to a calibration data set. The impact of a 2-mT magnetic stray field on the force output is limited to 0.3% of the full scale-about two orders magnitude improvement over the prior art. The force resolution is 2.7 mN and remains competitive. Furthermore, an on-chip temperature sensor and an algorithm are used to compensate the intrinsic thermal drift in the range 0-50°C. To validate the proper force regulation in spite of a nearby magnet, we integrated our prototype into a robotic hand. Our results demonstrate the robustness of 3D magnetic force sensors in the presence of real-world parasitic disturbances.

Encouraging and Detecting Preferential Incipient Slip for Use in Slip Prevention in Robot-Assisted Surgery

“…However, scale remains an issue with respect to manufacturing. Recent advances in Hall-effect sensor development will aid the development of more compact systems in the future [ 29 ]. Tissue properties: The current sensor system and method have been demonstrated to be effective at detecting incipient slip of porcine liver samples despite the lack of optimisation of the sensor design or detection algorithm for this target.…”

“…However, scale remains an issue with respect to manufacturing. Recent advances in Hall-effect sensor development will aid the development of more compact systems in the future [ 29 ].…”

Mass-Manufacturable 3D Magnetic Force Sensor for Robotic Grasping and Slip Detection

“…Figure 1 depicts the sensor concept and the actual realization side-by-side. As in the previous work [ 27 ], a single TSSOP16 package (5 × 4 mm 2 ) contains two side-by-side CMOS dies. In the previous work, the system was blind to the magnetic field in the Y-direction due to the challenges of integrating multiple 3D magnetic pixels inside the same package.…”

“…Moreover, samarium cobalt magnets also exhibit a lower thermal drift during operation, facilitating thermal compensation. The present design is compatible with the temperature compensation, based on the on-chip temperature sensor, we introduced earlier [ 27 ].…”

“…In a previous work [ 27 ], we showed that the key performance limitation of this technology, namely its over-sensitivity to magnetic stray fields, could be addressed in the chip design domain, by using a multi-pixel approach operating differentially to reject stray fields. A further key issue associated with these magnetic-based force sensors is linked to the manufacturing process, specifically embedding the magnet within the soft elastomer.…”