## 2 Materials and Methods  
### Sensor Glove System  
The sensor glove system is a prototype designed to optimally fit the hands of a selected number of male operators with comparable hand dimensions in the context of a study on grip force control in expert surgeons and novices manipulating a robotic assistant for minimally invasive surgery [2; 3; 4; 5; 6]. It consists of two sensor gloves, one for the right and one for the left hand, designed to measure hand grip strength. In this study, two identical cylindrical weight handles had to be lifted with dominant and non-dominant hands simultaneously by healthy young male subjects with about equally sized hands. The Force Sensitive Resistors (FSRs) embedded in the gloves permit recording grip force signals locally in twelve different locations of the inner left and right hands in a variety of grip tasks for a variety of different objects. Which sensors will be optimally activated in a given task when gripping objects depends on parameters relative to the size and shape of the object being gripped, and on the type of manipulation required by the task in a given context. This is discussed extensively in our previous work [2; 3; 4; 5; 6]. For gripping the cylindrical objects in this experiment, sensors producing consistent and reliable signal sequences during the whole time of task execution were placed on the middle phalanges of the index, middle, and ring fingers of each hand (Figure 1). The FSR diameter was 5 mm, and each of them was soldered to a 10 K\(\Omega\) pull-down resistor, creating a voltage divider. The voltage value as read out from the Arduino is given by  
\[Vout=RPDV3.3/(RPD+RFSR) \tag{1}\]  
where \(RPD\) indicates the resistance of the pull-down resistor, \(RFSR\) that of the corresponding FSR, and \(V3.3\) the 3.3 V supply voltage. The generated voltage varies monotonically between 0 and 3.22 Volts as a function of the force applied and is assumed to be uniform across the sensor surface. In the experimental task here, forces applied did not exceed 1100 g (g), which corresponds to \(\sim\)10 Newton. The relation between force and voltage is linear, as shown here below in Figure 2, within the range of millivolt (mV) measured in the experiments. All sensors were individually calibrated prior to the experiments, ensuring that all of them provided reliable output. Regulated 3.3 V was provided to each of the sensors via the Arduino. Power generated by a 4.2 V Li-Po battery enabled using the glove system without any cable connections. The combination of hardware and software design here provides accurate and reliable real-time sensing of grip strength signals by wearable technology. There were no weak current incidents, as the battery voltage levels and the voltages received from the gloves were continuously computer monitored in real time during the duration of all experiments. Values were displayed continuously on the screen of the user interface, and the software design ensured that, in case the battery level drops below 3.7 V, a warning  
Figure 1: The three task-relevant force-sensitive resistors (FSR) of the glove system for which recordings were analysed, located on the middle phalanges of index (M1), middle (M2), and ring fingers (M3) at identical, mirror-symmetric positions of the five participants’ compatibly dimensioned dominant and non-dominant hands. Figure 2: Static force in grams is related by a linear function (blue line) to tension output in the range from 50 mV to 1500 mV. signal is given, indicating to change or re-charge the battery. This never occurred during any of the experiments. Bluetooth-enabled wireless communication at a rate of 115,200 bits per second (bps) ensured communication between the glove system and the CPU of the computer for data storage. The electrical connections of the FSRs were individually routed via the dorsal side of each hand to the Arduino microcontroller on the forearm, as shown here below in Figure 3a.