Abstract
This paper presents a novel method to compensate for hysteresis nonlinearities observed in the response of a tactile sensor. The External Loop Adaptation Method (ELAM) performs a piecewise linear mapping of the experimentally measured external curves of the hysteresis loop to obtain all possible internal cycles. The optimal division of the input interval where the curve is approximated is provided by the error minimization algorithm. This process is carried out off line and provides parameters to compute the split point in real time. A different linear transformation is then performed at the left and right of this point and a more precise fitting is achieved. The models obtained with the ELAM method are compared with those obtained from three other approaches. The results show that the ELAM method achieves a more accurate fitting. Moreover, the involved mathematical operations are simpler and therefore easier to implement in devices such as Field Programmable Gate Array (FPGAs) for real time applications. Furthermore, the method needs to identify fewer parameters and requires no previous selection process of operators or functions. Finally, the method can be applied to other sensors or actuators with complex hysteresis loop shapes.
Highlights
Tactile sensors are arrays of force sensing units or taxels
Most of them are based on piezoresistive [6,7,8] or capacitive principles [9,10,11], other transduction principles such as optical [12] or piezoelectric [13] have been exploited. All these sensors show common errors in its operation such as hysteresis, nonlinearity and mismatching [14,15], so it is necessary to compensate these errors to obtain a more precise response. This compensation has to be carried out in highly demanding real time tasks, so smart tactile sensors with local electronics powerful enough to process the large amount of data from the sensor array in real time are required
The authors have proposed smart tactile sensors with local electronics based on FPGAs [16,17]
Summary
Tactile sensors are arrays of force sensing units or taxels. They are used in robotics to detect contact with objects [1,2,3], for instance in handling applications to improve the dexterity of artificial robotic hands [4,5]. Is proposed in [29] to independently characterize the ascending and descending branches of a piezoelectric actuator hysteresis loop Another alternative for the modeling and compensation of the asymmetrical hysteresis nonlinearities is a modified Prandtl-Ishlinskii model (MPI) described in [30], which replaces the linear input function of the classical play operator by a generalized input function based on a third-order polynomial. This paper presents a new method to model and compensate hysteresis nonlinearities based on the adaptation of the external loop ( we call it ELAM) It is a phenomenological model, which builds two continuous and monotonic curves, one increasing and the other decreasing, from linear interpolation of the experimentally measured hysteresis external loop.
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