Stanford Advisors

All Publications

  • Multimodal sensing and intuitive steering assistance improve navigation and mobility for people with impaired vision. Science robotics Slade, P., Tambe, A., Kochenderfer, M. J. 2021; 6 (59): eabg6594


    [Figure: see text].

    View details for DOI 10.1126/scirobotics.abg6594

    View details for PubMedID 34644159

  • An open-source and wearable system for measuring 3D human motion in real-time. IEEE transactions on bio-medical engineering Slade, P., Habib, A., Hicks, J. L., Delp, S. L. 2021; PP


    OBJECTIVE: Analyzing human motion is essential for diagnosing movement disorders and guiding rehabilitation for conditions like osteoarthritis, stroke, and Parkinson's disease. Optical motion capture systems are the standard for estimating kinematics but require expensive equipment located in a predefined space. While wearable sensor systems can estimate kinematics in any environment, existing systems are generally less accurate than optical motion capture. Many wearable sensor systems require a computer in close proximity and use proprietary software, limiting experimental reproducibility.METHODS: Here, we present OpenSenseRT, an open-source and wearable system that estimates upper and lower extremity kinematics in real time by using inertial measurement units and a portable microcontroller.RESULTS: We compared the OpenSenseRT system to optical motion capture and found an average RMSE of 4.4 degrees across 5 lower-limb joint angles during three minutes of walking and an average RMSE of 5.6 degrees across 8 upper extremity joint angles during a Fugl-Meyer task. The open-source software and hardware are scalable, tracking 1 to 14 body segments, with one sensor per segment. A musculoskeletal model and inverse kinematics solver estimate Kinematics in real-time. The computation frequency depends on the number of tracked segments, but is sufficient for real-time measurement for many tasks of interest; for example, the system can track 7 segments at 30 Hz in real-time. The system uses off-the-shelf parts costing approximately 100 USD plus 20 for each tracked segment.SIGNIFICANCE: The OpenSenseRT system is validated against optical motion capture, low-cost, and simple to replicate, enabling movement analysis in clinics, homes, and free-living settings.

    View details for DOI 10.1109/TBME.2021.3103201

    View details for PubMedID 34383640

  • Sensing leg movement enhances wearable monitoring of energy expenditure. Nature communications Slade, P., Kochenderfer, M. J., Delp, S. L., Collins, S. H. 2021; 12 (1): 4312


    Physical inactivity is the fourth leading cause of global mortality. Health organizations have requested a tool to objectively measure physical activity. Respirometry and doubly labeled water accurately estimate energy expenditure, but are infeasible for everyday use. Smartwatches are portable, but have significant errors. Existing wearable methods poorly estimate time-varying activity, which comprises 40% of daily steps. Here, we present a Wearable System that estimates metabolic energy expenditure in real-time during common steady-state and time-varying activities with substantially lower error than state-of-the-art methods. We perform experiments to select sensors, collect training data, and validate the Wearable System with new subjects and new conditions for walking, running, stair climbing, and biking. The Wearable System uses inertial measurement units worn on the shank and thigh as they distinguish lower-limb activity better than wrist or trunk kinematics and converge more quickly than physiological signals. When evaluated with a diverse group of new subjects, the Wearable System has a cumulative error of 13% across common activities, significantly less than 42% for a smartwatch and 44% for an activity-specific smartwatch. This approach enables accurate physical activity monitoring which could enable new energy balance systems for weight management or large-scale activity monitoring.

    View details for DOI 10.1038/s41467-021-24173-x

    View details for PubMedID 34257310

  • Rapid energy expenditure estimation for ankle assisted and inclined loaded walking. Journal of neuroengineering and rehabilitation Slade, P. n., Troutman, R. n., Kochenderfer, M. J., Collins, S. H., Delp, S. L. 2019; 16 (1): 67


    Estimating energy expenditure with indirect calorimetry requires expensive equipment and several minutes of data collection for each condition of interest. While several methods estimate energy expenditure using correlation to data from wearable sensors, such as heart rate monitors or accelerometers, their accuracy has not been evaluated for activity conditions or subjects not included in the correlation process. The goal of our study was to develop data-driven models to estimate energy expenditure at intervals of approximately one second and demonstrate their ability to predict energetic cost for new conditions and subjects. Model inputs were muscle activity and vertical ground reaction forces, which are measurable by wearable electromyography electrodes and pressure sensing insoles.We developed models that estimated energy expenditure while walking (1) with ankle exoskeleton assistance and (2) while carrying various loads and walking on inclines. Estimates were made each gait cycle or four second interval. We evaluated the performance of the models for three use cases. The first estimated energy expenditure (in Watts) during walking conditions for subjects with some subject specific training data available. The second estimated all conditions in the dataset for a new subject not included in the training data. The third estimated new conditions for a new subject.The mean absolute percent errors in estimated energy expenditure during assisted walking conditions were 4.4%, 8.0%, and 8.1% for the three use cases, respectively. The average errors in energy expenditure estimation during inclined and loaded walking conditions were 6.1%, 9.7%, and 11.7% for the three use cases. For models not using subject-specific data, we evaluated the ability to order the magnitude of energy expenditure across conditions. The average percentage of correctly ordered conditions was 63% for assisted walking and 87% for incline and loaded walking.We have determined the accuracy of estimating energy expenditure with data-driven models that rely on ground reaction forces and muscle activity for three use cases. For experimental use cases where the accuracy of a data-driven model is sufficient and similar training data is available, standard indirect calorimetry could be replaced. The models, code, and datasets are provided for reproduction and extension of our results.

    View details for DOI 10.1186/s12984-019-0535-7

    View details for PubMedID 31171003

  • Estimation and control using sampling-based Bayesian reinforcement learning IET Cyber-Physical Systems: Theory & Applications Slade, P., Sunberg, Z. N., Kochenderfer, M. J. 2019; 5 (1): 127-135
  • Stanford Doggo: An Open-Source, Quasi-Direct-Drive Quadruped Kau, N., Schultz, A., Ferrante, N., Slade, P., IEEE, Howard, A., Althoefer, K., Arai, F., Arrichiello, F., Caputo, B., Castellanos, J., Hauser, K., Isler, Kim, J., Liu, H., Oh, P., Santos, Scaramuzza, D., Ude, A., Voyles, R., Yamane, K., Okamura, A. IEEE. 2019: 6309–15
  • Simultaneous active parameter estimation and control using sampling-based Bayesian reinforcement learning Slade, P., Culbertson, P., Sunberg, Z., Kochenderfer, M., Bicchi, A., Okamura, A. IEEE. 2017: 804–10
  • Design of a Soft Catheter for Low-Force and Constrained Surgery Slade, P., Gruebele, A., Hammond, Z., Raitor, M., Okamura, A. M., Hawkes, E. W., Bicchi, A., Okamura, A. IEEE. 2017: 174–80