Dexterity in robotic hands is not enough to cover the demands for more flexibility in the manufacturing process. Specifically, processes that involve cooperation or learning from humans, slippage detection and tactile feedback to improve grasp stability when different objects are manipulated, object exploration and classification, quality inspection, welding, etc. The sense of touch is the key to the capabilities of human hands, so tactile sensors must be incorporated into robotic hands to improve them. However, tactile sensing technology is not yet mature enough to be an effective tool. One reason for this limited performance is the need of acquisition and processing of large amounts of data in the short time required to perform a fluent manipulation. Smart tactile sensors can help in this goal if they are able to carry out local acquisition and processing of tactile data and transmit only relevant information through buses that guarantee bounded latency. Field-programmable gate arrays (FPGAs) are devices which are especially suitable for this task due to their ability for parallel processing. This paper presents the realization of electronics for a tactile sensor suite based on FPGAs that implements a direct interface with the raw sensor and serial communication between the fingertips and palm.

One of the most efficient ways to connect a resistive sensor array is using columns and rows in a 2-D structure. The main problem in this implementation is crosstalk appearing due to non-idealities in the readout circuits. Crosstalk causes measurement errors which restrict the usable range in array size or resistive sensors values. This paper analyses the way in which these factors affect accuracy, setting out a new approach to eliminate or reduce their influence based on just an additional operational amplifier and some calibration resistors without a significant increase in readout time. The first method involves introducing an additional column in order to eliminate the combined effect of the output resistance buffers for row selection, offset voltages and bias current of the operational amplifier. In the second method, a row of resistors is added in order to reduce the effect of finite gains. Theoretical analysis has been performed and validated by simulation. Results show that an improvement in accuracy compared with other proposals in the literature is possible.

The typical layout in a piezoresistive tactile sensor arranges individual sensors to form an array with M rows and N columns. While this layout reduces the wiring involved, it does not allow the values of the sensor resistors to be measured individually due to the appearance of crosstalk caused by the nonidealities of the array reading circuits. In this paper, two reading methods that minimize errors resulting from this phenomenon are assessed by designing an electronic system for array reading, and the results are compared to those obtained using the traditional method, obviating the nonidealities of the reading circuit. The different models were compared by testing the system with an array of discrete resistors. The system was later connected to a tactile sensor with 8 × 7 taxels.

One of the most suitable ways of distributing a resistive sensor array for reading is an array with M rows and N columns. This allows reduced wiring and a certain degree of parallelism in the implementation, although it also introduces crosstalk effects. Several types of circuits can carry out the analogue-digital conversion of this type of sensors. This article focuses on the use of operational amplifiers with capacitive feedback and FPGAs for this task. Specifically, modifications of a previously reported circuit are proposed to reduce the errors due to the non-idealities of the amplifiers and the I/O drivers of the FPGA. Moreover, calibration algorithms are derived from the analysis of the proposed circuitry to reduce the crosstalk error and improve the accuracy. Finally, the performances of the proposals is evaluated experimentally on an array of resistors and for different ranges.

Resistive sensor arrays are formed by a large number of individual sensors which are distributed in different ways. This paper proposes a direct connection between an FPGA and a resistive array distributed in M rows and N columns, without the need of analog-to-digital converters to obtain resistance values in the sensor and where the conditioning circuit is reduced to the use of a capacitor in each of the columns of the matrix. The circuit allows parallel measurements of the N resistors which form each of the rows of the array, eliminating the resistive crosstalk which is typical of these circuits. This is achieved by an addressing technique which does not require external elements to the FPGA. Although the typical resistive crosstalk between resistors which are measured simultaneously is eliminated, other elements that have an impact on the measurement of discharge times appear in the proposed architecture and, therefore, affect the uncertainty in resistance value measurements; these elements need to be studied. Finally, the performance of different calibration techniques is assessed experimentally on a discrete resistor array, obtaining for a new model of calibration, a maximum relative error of 0.066% in a range of resistor values which correspond to a tactile sensor.