Test 2—Sensor data

(**a**) Inclination versus time through inertial sensor measurements for 30◦ inclination.

(**b**) Orientation versus time through inertial sensor measurements for 30◦ inclination.

(**c**) Inclination versus time through inertial sensor measurements for 45◦ inclination.

(**d**) Orientation versus time through inertial sensor measurements for 45◦ inclination.

(**e**) Inclination versus time through inertial sensor measurements for 60◦ inclination.

(**f**) Orientation versus time through inertial sensor measurements for 60◦ inclination.

**Figure 21.** Test 2—Sensor data. Fixed 30◦, 45◦ and 60◦ inclination for a 360◦ rotation. The blue line is the experimental data obtained from the encoder and the orange dotted line is the reference.

#### **5. Discussion**

Simulation and experimental results have been performed to analyze and validate both the design and the proposed model for the cable-driven soft joint.

The simulation results allow the validation of the soft joint through a finite element study. The soft joint was simulated by applying a load of 60 N, which would be the maximum force expected for this prototype. It has made possible to validate the joint structure, ensuring that when maximum loads are applied, the structure does not exceed the elastic limit and does not lose its elasticity.

The experimental tests performed show the behavior of the soft joint system in different situations. Test 1 explores the behavior to reach a target position from a resting position and how the soft link behaves to return to the home position. It is a movement where the

inclination changes with a fixed orientation that does not vary. Test 2 explores the ability to maintain a fixed inclination while gradually varying the orientation.

## *5.1. Results Using the Encoder Sensor*

The inclination results, obtained from the encoder during Test 1, show that the experimental inclination reaches the reference inclination, and this is repeated for each of the four requested orientations. We also observed that the higher the requested reference, the longer it takes to reach it.

For the orientation results, the orientation reference is a set of four steps of different sizes. The first is a step of zero amplitude and the experimental orientation is quickly reached. This is because, from the zero-degree inclination position (fully extended joint), reaching any orientation is almost immediate. When the joint is requested to return to the resting position, the experimental orientation remains constant. Meanwhile, the inclination decreases and when it reaches zero, the orientation reaches zero, too. This is why, in this test, the orientation values change so quickly back to zero degrees and the time between the reference orientation and the experimental orientation reaching zero is longer.
