## 2 Materials and Methods  
### Pinch Data Acquisition System  
The experimental setup of the data acquisition system is described in Figure 2. It consists of:  
1. Displacement sensor: LVDT sensor (1) with Low Pass Filter (9). 2. Linear actuator system: including linear electric actuator (2) and servo motor driver (8). 3. Customized Pinch force load cell: pincer object (4), Wheatstone bridge (5), and an amplifier (6). 4. Pulling force load cell: load cell (3) and an amplifier (11). 5. Data acquisition card: Arduino(r) Due board (Arduino LLC, Torino, Italy) (11) and Arduino(r) IDE 1.8.5 software (arduino.cc) [50]. 6. DC power supply (7). In our previous work [51], a customized pinch force load cell based on strain gauge was designed, fabricated, and calibrated. The customized pinch force load cell is composed of three parts: pincer object, strain gauge, and signal conditioning circuit. The pincer object was fabricated to mimic a pencil, as used in UE-FMA, which represents a cylindrical object with a diameter of 12 mm and 150 mm length. In order for a strain gauge to measure the bending at the pinching location near the free edge of the pincer object, a 4 mm slot cut was created, as shown in Figure 3. The slot cut starts from the free end to the middle of the pincer object, similar to the shape of a tuning fork. The pinching location is within 20 mm from the free edge and is adequate to cover the fingertip length. A 350-ohm strain gauge (SGK-L1-D-K350P-PC11-E) was placed at the maximum stress point. The maximum stress point was determined based on the stress analysis performed using ANSYS(r) finite element software (Version 15.0, ANSYS Inc, Canonsburg, PA, USA) as shown in Figure 4. The conditioning circuit consists of a quarter Wheatstone bridge and an amplifier. The quarter Wheatstone bridge was implemented to convert the strain gauge resistance change to voltage change when pinching occurs. However, the voltage change was too small. Thus, a commercial amplifier (Wachendorff Strain Gauge Converter(r), SENECA s.r.l., Padova, Italy) with a gain of 1000 was used. Figure 2: Experimental Setup of data acquisition system for pinch assessment. The standard strain gauge calibration of force-voltage is usually performed for one contact location only. However, in the pinch test of UE-FMA, the contact location may vary due to the different initial pinching location of each volunteer. Furthermore, the contact location may also vary during the automatic pull, which causes slipping. Therefore, a continuous relationship of force-voltage for all possible contact points along the pinching length is required. This can be achieved by performing a multipoint calibration at five contact points away from the free edge (4.1, 5.8, 11.5, 16.5, and 20.2 mm). The multipoint calibration was performed using a mechanical testing system (INSTRON(r) 3366, Illinois Tool Works Inc, Norwood, MA, USA) by applying dynamic loading (0-50 N), as shown in Figure 5. The pincer object was held stationary on the INSTRON(r) 3366 base during calibration by applying glue on both sides of the pincer object to prevent any movement, as shown in Figure 5. As a result, five force-voltage curves were generated, as depicted in Figure 6a. The voltage and force data were recorded from the customized pinch force load cell and the INSTRON(r) 3366 machine. Subsequently, the continuous relationship of force as a function of voltage and position was modeled using linear regression function, as depicted in Figure 6b. The linear correlation coefficient R\({}^{2}\) of 0.9896 indicates high linearity. Using the linear plane model equation (Equation (1)), the force measurements can be estimated at any contact point within pinching length given the measurements of voltage and position, which were collected from the pinch force load cell and the LVDT sensor, respectively.