Ho Jung Choi

All Publications

• Additively manufactured micro-lattice dielectrics for multiaxial capacitive sensors. Science advances Berman, A., Hsiao, K., Root, S. E., Choi, H., Ilyn, D., Xu, C., Stein, E., Cutkosky, M., DeSimone, J. M., Bao, Z. 2024; 10 (40): eadq8866

  Abstract

  Soft sensors that can perceive multiaxial forces, such as normal and shear, are of interest for dexterous robotic manipulation and monitoring of human performance. Typical planar fabrication techniques have substantial design constraints that often prohibit the creation of functionally compelling and complex architectures. Moreover, they often require multiple-step operations for production. Here, we use an additive manufacturing process based on continuous liquid interface production to create high-resolution (30-micrometer) three-dimensional elastomeric polyurethane lattices for use as dielectric layers in capacitive sensors. We show that the capacitive responses and sensitivities are highly tunable through designs of lattice type, thickness, and material-void volume percentage. Microcomputed tomography and finite element simulation are used to elucidate the influence of lattice design on the deformation mechanism and concomitant sensing behavior. The advantage of three-dimensional printing is exhibited with examples of fully printed representative athletic equipment with integrated sensors.

  View details for DOI 10.1126/sciadv.adq8866

  View details for PubMedID 39365852

• Design and Evaluation of a 3-DoF Haptic Device for Directional Shear Cues on the Forearm. IEEE transactions on haptics Yoshida, K. T., Zook, Z. A., Choi, H., Luo, M., O'Malley, M. K., Okamura, A. M. 2024; 17 (3): 483-495

  Abstract

  Wearable haptic devices on the forearm can relay information from virtual agents, robots, and other humans while leaving the hands free. We introduce and test a new wearable haptic device that uses soft actuators to provide normal and shear force to the skin of the forearm. A rigid housing and gear motor are used to control the direction of the shear force. A 6-axis force/torque sensor, distance sensor, and pressure sensors are integrated to quantify how the soft tactor interacts with the skin. When worn by participants, the device delivered consistent shear forces of up to 0.64 N and normal forces of up to 0.56 N over distances as large as 14.3 mm. To understand cue saliency, we conducted a user study asking participants to identify linear shear directional cues in a 4-direction task and an 8-direction task with different cue speeds, travel distances, and contact patterns. Participants identified cues with longer travel distances best, with an 85.1% accuracy in the 4-direction task, and a 43.5% accuracy in the 8-direction task. Participants had a directional bias, with a preferential response in the axis towards and away from the wrist bone.

  View details for DOI 10.1109/TOH.2024.3365669

  View details for PubMedID 38349838

• Integrated Pneumatic Sensing and Actuation for Soft Haptic Devices IEEE ROBOTICS AND AUTOMATION LETTERS Choi, H., Cutkosky, M. R., Stanley, A. A. 2023; 8 (11): 7591-7598

  View details for DOI 10.1109/LRA.2023.3320494

  View details for Web of Science ID 001085222400005

• Perceived Intensities of Normal and Shear Skin Stimuli Using a Wearable Haptic Bracelet IEEE ROBOTICS AND AUTOMATION LETTERS Sarac, M., Huh, T., Choi, H., Cutkosky, M. R., Di Luca, M., Okamura, A. M. 2022; 7 (3): 6099-6106

  View details for DOI 10.1109/LRA.2021.3140132

  View details for Web of Science ID 000785670500003

• Deep Learning Classification of Touch Gestures Using Distributed Normal and Shear Force Choi, H., Brouwer, D., Lin, M. A., Yoshida, K. T., Rognon, C., Stephens-Fripp, B., Okamura, A. M., Cutkosky, M. R., IEEE IEEE. 2022: 3659-3665

  View details for DOI 10.1109/IROS47612.2022.9981457

  View details for Web of Science ID 000908368202109

• Exploratory Hand: Leveraging Safe Contact to Facilitate Manipulation in Cluttered Spaces IEEE ROBOTICS AND AUTOMATION LETTERS Lin, M. A., Thomasson, R., Uribe, G., Choi, H., Cutkosky, M. 2021; 6 (3): 5159-5166

  View details for DOI 10.1109/LRA.2021.3068941

  View details for Web of Science ID 000645056800009

• Dynamically Reconfigurable Tactile Sensor for Robotic Manipulation IEEE ROBOTICS AND AUTOMATION LETTERS Huh, T., Choi, H., Willcox, S., Moon, S., Cutkosky, M. R. 2020; 5 (2): 2562–69

  View details for DOI 10.1109/LRA.2020.2972881

  View details for Web of Science ID 000526521500019

• Using force data to self-pace an instrumented treadmill and measure self-selected walking speed. Journal of neuroengineering and rehabilitation Song, S. n., Choi, H. n., Collins, S. H. 2020; 17 (1): 68

  Abstract

  Self-selected speed is an important functional index of walking. A self-pacing controller that reliably matches walking speed without additional hardware can be useful for measuring self-selected speed in a treadmill-based laboratory.We adapted a previously proposed self-pacing controller for force-instrumented treadmills and validated its use for measuring self-selected speeds. We first evaluated the controller's estimation of subject speed and position from the force-plates by comparing it to those from motion capture data. We then compared five tests of self-selected speed. Ten healthy adults completed a standard 10-meter walk test, a 150-meter walk test, a commonly used manual treadmill speed selection test, a two-minute self-paced treadmill test, and a 150-meter self-paced treadmill test. In each case, subjects were instructed to walk at or select their comfortable speed. We also assessed the time taken for a trial and a survey on comfort and ease of choosing a speed in all the tests.The self-pacing algorithm estimated subject speed and position accurately, with root mean square differences compared to motion capture of 0.023 m s -1 and 0.014 m, respectively. Self-selected speeds from both self-paced treadmill tests correlated well with those from the 10-meter walk test (R>0.93,p<1×10-13). Subjects walked slower on average in the self-paced treadmill tests (1.23±0.27 ms-1) than in the 10-meter walk test (1.32±0.18 ms-1) but the speed differences within subjects were consistent. These correlations and walking speeds are comparable to those from the manual treadmill speed selection test (R=0.89,p=3×10-11;1.18±0.24 ms-1). Comfort and ease of speed selection were similar in the self-paced tests and the manual speed selection test, but the self-paced tests required only about a third of the time to complete. Our results demonstrate that these self-paced treadmill tests can be a strong alternative to the commonly used manual treadmill speed selection test.The self-paced force-instrumented treadmill well adapts to subject walking speed and reliably measures self-selected walking speeds. We provide the self-pacing software to facilitate use by gait researchers and clinicians.

  View details for DOI 10.1186/s12984-020-00683-5

  View details for PubMedID 32493426