Author: Yu Hang He
Email: hey6@unlv.nevada.edu
Date Last Modified: 08/06/2018

This week, I went on a tour to visit the Demilitarized Zone between North and South Korea. The DMZ is a 4 km wide area between the North and South Korea after the ceasefire agreement during Korean War. The DMZ was marked with warfare, death, and conflict during the Korean War. Yet, today it is a strip of lush and green forest land. The buildings in the distance are within territories of North Korea.

During the tour, I was able to visit the Third Tunnel, the Third Tunnel was an deep underground tunnel that North Korea prepared to invade Seoul. The tunnel was dug after the ceasefire agreement, demonstrating the ongoing conflict between North and South Korea. In addition, I visited the only operational train station between North and South Korea. I gained a deeper understanding of the conflict between North and South Korea and South Korean's hope for reunification.

The Korean War tremendously impacted the Korean culture and history

Staying in Korea constantly prompt me to be reminiscent of my childhood in China. Many aspect of Korean culture, from food to tradition, appears to me as quite similar to Chinese culture. The similarity reminded me how much I missed my birthplace. I was too concentrated on my daily life in American before to think back to my childhood and birthplace. Even though it has been 8 years since I left my birthplace, I still hold many fond memory of my old home.

Last week, I implement the inverse kinematic function and created PODO AL that will transform mocap data to joint data and execute the motion. This week, I focused on filtering the data and implementing joint angle, velocity, and acceleration limit on the output joint data.

The implementation of joint limit turn out to be more of a challenge then I anticipated. The simplest method to apply joint angle constraint is to limit the angles once they exceed maximum or minimum. The simplest method to limit joint angle velocity and acceleration is to apply a time warp to slow down motion within velocity and acceleration limit. However, both method are not suitable for the project because this project aim at preserving as much original characteristic of motion as possible.

In order to accomplish this, I decided to implement the filters developed by Pollard et al. Here are the result of implementation.

Joint angle limit:
The blue lines are the original joint angles and the green lines are joint angles after applying joint angle limit and filtering. The algorithm is not perfect, however, it was able to limit the joint angles while preserving some characteristics of original motion.

Joint velocity limit:
Again, the blue lines are the original joint angles and green lines are joint angles after applying joint velocity limit and filtering. One problem I noticed for this algorithm is that, for relatively small amount of velocity exceed the limit, the algorithm worked very well. However, once the velocity and acceleration exceeds the limit, the filter will result in a flat angle.

Another problem I noticed is that the first set of data I collected using mocap system are inaccurate and inconsistent. I need to collect more data from mocap system this week and test the filtering.