# A Neuro-Prosthetic Device for Substituting Sensory Functions during Stance Phase of the Gait
## 3 Results and Discussion
### Results of Balancing Strategies  
To test the balancing device, we must first mimic the abnormal condition with our test-bed. We gradually change the hip, knee, and hock angles of the left robot limb in order to change the orientation of the pelvis. We assumed the critical value for pelvic orientation when a dog is at risk of falling is 10 degrees. We adjusted both legs at typical stance positions for a dog, with hip, knee and hock joint angles around 101, 140, and 129 degrees, respectively. We ran the left limb with Teensy #2 to produce abnormality in pelvic orientation that can be recognized by IMU #1 and Teensy #1 (device analytical core). Figure 13 shows the pelvic orientation changed from 0 to around 12 degrees in 5 s. This mimics the situation when a dog falls from the left. When the left limb starts falling, it causes some noise at start-up which doesn't affect the balancing test results. This noise is around three seconds in Figure 13.  
Now that we can mimic falling, we used our proposed strategies to test the robot response to stimulation and balancing device functionality. Using the angle measurements from IMU #1, we monitor the hip angle. When the angle exceeded the threshold of 10 degrees, the balancing device produced a stimulation command based on the selected strategy. The device selected the maximum  
Figure 12: Filtered hip angular velocities from gyroscope readings and from calculations. Figure 13: Pelvis orientation during falling. inclined angle read by IMU #1 as \(\alpha\) in Equation (1), read IMU #2, 3 and 4 to find hip, knee, and hock joint angles including those before stimulation, and calculated the final angles based on each of our strategies. Finally, it applied stimulation voltage to joint motors to balance the pelvis. We used our joint potentiometers as our reference for IMUs' data accuracy check. Figures 14-16 show the robot hip, knee, and hock joint responses to stimulation, respectively, based on strategy #1. In each of these figures, we have plotted the pelvis orientation at (a). As seen, when the pelvis declines more than 10 degrees, stimulation starts, and it gets balanced immediately. At (b), we have shown the stimulation command calculated by [PERSON] and output joint angles found from IMU readings. At (c), the joint angles found by IMUs are compared with potentiometers readings. Results show a good match between the two. Based on strategy #1, the knee joint is kept fixed during stimulation. This has been shown in Figure 15b, c. The hip joint angle increases, and hock joint angle decreases to level the pelvis as shown in Figures 14 and 16b,c. Figure 16: Stimulation results based on strategy #1 (**a**) pelvic orientation, (**b**) robot hock joint response, (**c**) comparison of angles found from IMU readings with potentiometers. Figure 15: Stimulation results based on strategy #1 (**a**) pelvis orientation, (**b**) robot knee joint response, (**c**) comparison of angles found from IMU readings with potentiometers. The robot hip, knee, and hock joint responses to stimulation based on strategy #2 are shown in Figures 17-19, respectively, with pelvic orientation changes in (a), joint response in (b), and potentiometer reading comparison in (c). Based on this second strategy, the hip joint is kept fixed. During the experiment on the test-bed, when the knee and hock joints move, they may cause a little motion in the hip joint, but the motor at this joint returns the femur to the initial position. This causes a little noise in our reading for both IMUs and potentiometer. If the device is used for a live animal and it is not able to fix the movement at the hip joint, stimulation must be applied to surrounding muscles to prevent this motion. To balance the hip, both knee and hock joints angles decrease as shown in Figures 18 and 19,c. Figure 17: Stimulation results based on strategy #2 (**a**) pelvic orientation, (**b**) robot hip joint response, (**c**) comparison of angles found from IMU readings with potentiometers. Strategy #3 experimental results are shown in Figures 20-22.