Research Statement

 Ongoing Research

Archived Research

 0. Compact Non-Contact Transmission Mechanism:

1. TSA-based Miniature Transmission Mechanism: 

Electric motors have a very narrow nominal speed-torque operating range due to their thermal and mechanical limitations. Operations beyond these limitations may result in permanent damage to the motor windings and mechanical components. Additional mechanisms such as cooling or conventional input-output transmission mechanisms (e.g., multi-ratio transmission and continuously variable transmission in an automobile) may provide an expanded operation area, but they have a large volume and are complex structures, which makes it difficult to miniaturize the total actuation system. To implement a compact transmission manner, I proposed twisted string actuation (TSA)-based compact transmission mechanism. TSA is a rotary-to-linear transmission and has a very light, compact, and flexible structure; its transmission ratio can vary with the radius of twisted string. The developed drive module can automatically change the radius of the twisted string and achieve 2-speed transmission ratios. Due to the compliance and compactness of TSA, the transmission part has a dimension of 20.7x20.7x20.1mm3 and achieves an approximately 6 times speed or force output depending on the transmission stage. This mechanism was effectively employed for mobile robots such as robotic hands and grippers to expand their limited operational range and provide various grasping strategies. Due to the high nonlinearity of state dependent TSA transmission ratio and friction from the mechanical structure, I implemented a double-loop disturbance observer (DOB) to compensate for these disturbances and provide linear control performance with a designed controller.

1 - A) Applications : Robot hand

2. Miniature Force Sensor: 

Over the last several decades, the field of robotics has been rapidly improved in novel actuation, transmission mechanisms, and control algorithms. At the same time, compact and high precision force/displacement sensors have become essential to implementing precise and dexterous feedback control performance. In particular, robotic hands and medical devices require high precision force sensors with miniaturized dimensions in a compact system. However, the cost of these sensors drastically increases as the dimensions of the sensor are miniaturized, increasing the cost of the total system. I proposed an optics-based screen-type compact sensor providing: 1) a wide range of highly linear output and 2) a reliable output robust to external disturbances and manufacturing errors in a cost-effective manner. To implement the proposed concept, a miniature photo-interrupter (which consists of a LED and a phototransistor) and a dual-screen type elastic metal frame were used. The sensor has a dimension of 11.4x9.45x5 mm3 and provides 99.58% accuracy with 1.08% hysteresis and 0.83% hysteresis, which is comparable to that of commercial sensors, but is a much smaller size and cost-effective compared to existing sensor mechanisms. The developed sensor has been utilized for measuring a fingertip force of robotic hands/grippers and a tendon tension of medical robots, providing a high precision force feedback control


3. Steerable Surgical Robots

Minimally invasive surgical procedures with robotic devices have been shown to achieve a high success rate with minimal trauma. In this procedure, rigid and straight endoscopic instruments with surgical tools are inserted and used to operate at the target site in the body. However, conventional instruments have a difficulty in reaching operational target areas and have limited dexterity, particularly in the tortuous and complex organs or arteries, due to their inherent rigid structure. Therefore, achieving high dexterity in surgical robots remains a challenging issue in the minimally invasive treatment. To solve this problem, I contributed to the development of various types of surgical robots with a steerable capability, with an outer diameter (OD) ranging from 1.93mm to 0.41mm for various operational purposes. 

3 - A) For pediatric neurosurgery

I have contributed to develop a 2 DoF superelastic steerable continuum surgical robot with 1.93mm in OD. By using a tendon routing strategy with different joint stiffnesses, independently controllable joint motion can be achieved without any joint coupling issues. This robot allows the instruments to have high dexterity so that the insertion path across the brain can be optimized to reduce trauma. An in-depth hysteresis modeling of superelastic material (NiTi) and a design of model-based control were conducted in this study.

Related publication: 

3 - B) For endovascular treatment procedure

A very thin (<0.40mm) wire, which is called a ‘guidewire’, is inserted along the artery and a surgeon feeds and controls the guidewire to reach a target lesion. Then, the guidewire is used to guide an insertion of a catheter or sheath. Because of its ultra-thin dimension, the guidewire cannot have a steerable capability and has to be manually controlled by the surgeon with pre-curved shapes depending on the shape of arteries. 

 We (RoboMed research group, GeorgiaTech) firstly proposed a robotically steerable guidewire with 0.40mm in OD which is the smallest Tendon driven-robotic guidewire in the world. The extremely miniaturized design is implemented with a concentrically aligned multiple tubes structure.

Related publication: 

4. Wearable Hand Rehabilitation Glove

Spinal cord injury or stroke can result in the complete loss of motor function and control of hand movement. A physical therapy and rehabilitation can facilitate the recovery of hand functions in persons with degraded or nonexistent motor control. Therefore, a number of robotic rehabilitation devices have been developed to assist both patients and therapists during rehabilitation.

 I have contributed to develop ‘FLEXotendon Glove’ which is a wearable, soft, and tendon actuated hand exoskeleton for rehabilitation purposes. The exoskeleton was designed with 3D-printed customized parts and the biomimetic tendon routing strategy provides 4 DoF of finger movement, which allows the exoskeleton to form various grasping postures. It provides a voice-controlled user interface through a smartphone app for easy and intuitive commend. I investigated the overall design and actuation mechanism of the developed exoskeleton and have conducted human subject case studies with a patient with spinal cord injury to verify the performance of the device. Moreover, I proposed a FLEXotendon glove with a suction capability, which provides various grasping strategies and increases grasping performance.

Related publication: