Table 1.
Walking assist hip exoskeletons
| Exoskeleton | Summary of actuator features | Sensor | Gait phase | Torque generation | Device weight (kg) | References |
|---|---|---|---|---|---|---|
| SAS | Rigid actuator with motor and reducer | Foot switch | TBE | Database | 2.4 | Shimada et al., 2009 |
| XPED2 | The leaf spring at the foot will tighten the cable during hip extension and loosen the cable during hip flexion | NA | Threshold | NA | 6.91 | van Dijk and Van der Kooij, 2014 |
| SMA | Rigid actuator with motor and reducer | IMU | AO | Function | 2.8 | Buesing et al., 2015 |
| PH-EXOS | The force of the driving motors mounted behind the backpack is delivered to the joints of the exoskeleton | FSR Encoder | NA | Function | 3.5 | Wu et al., 2015 |
| APO | Actuation units employ an SEA architecture to achieve closed-loop control and flexibility | FSR | AO | NA | 4.2 | Giovacchini et al., 2015 |
| Harvard hip exosuit | Flexible actuator with motor and Bowden cable | IMU Force | TBE | Function | 6.5 | Asbeck et al., 2015 |
| GEMS | Rigid actuator with motor and reducer | Encoder IMU | AO | Function | 2.8 | Lee et al., 2017d |
| HeSA | Rigid actuator with motor and reducer | IMU | PO | NA | 2.95 | Sugar et al., 2017 |
| NREL-Exo | SEA-driven hip exoskeleton with powered hip flexion/extension and hip abduction/adduction | IMU FSR | FSM | Admittance shaping | 9.2 | Zhang et al., 2017 |
| Michigan exoskeleton | Pneumatic actuators around the hip joint provide hip flexion and extension assistance | Foot switch | FSM | Function | 6.8 | Young et al., 2017a |
| Michigan exoskeleton | Pneumatic actuators around the hip joint provide hip flexion and extension assistance | Electromyogram (EMG) | FSM | Function | 6.8 | Young et al., 2017b |
| Harvard exosuit | Flexible Bowden cable apply forces across joints in parallel with human muscles | IMU | TBE | Function | 5 | Lee et al., 2017a; Ding et al., 2018 |
| AWS | Pneumatic gel muscle (PGM) along the rectus femoris assist hip flexion | FSR | FSM | Function | 1.127 | Thakur et al., 2018 |
| Gatech exoskeleton | Flexible actuator with SEAs | IMU Encoder Force | TBE | Function | 7 | Kang et al., 2018, 2019 |
| APO | Actuation units employ an SEA architecture to achieve closed-loop control and flexibility | C-sens FSR | AO | NA | 4.2 | Crea et al., 2019 |
| FHAE | Flexible actuator with SEAs | IMU | AO | Database | 4.47 | Xue et al., 2019 |
| SIAT | Flexible exoskeleton with Bowden cable | IMU Encoder | CNN | Database | 4.6 | Chen et al., 2020 |
| QDD exoskeleton | Rigid exoskeleton using a compact direct-drive actuator | IMU Encoder | NN | Database | 3.4 | Yu et al., 2020 |
| HUST hip exoskeleton | The spring stores energy with the hip extension to its maximum extension position and releases the stored energy to assist hip flexion | NA | Threshold | NA | 1.305 | Zhou et al., 2021a |
| SUDA exosuit | Flexible actuator with SEAs and the series-wedge-structure is driven by Bowden cable | IMU Foot switch | FSM | Function | 1.4 | Zhang et al., 2021 |
| HUST hip-knee exoskeleton | The spring absorbs negative mechanical energy of the knee joint and then transfer the stored energy to assist hip musculature | NA | Threshold | NA | 1.86 | Zhou et al., 2021b |
| SIAT exosuit | Flexible actuator with Bowden cable | IMU force | NA | NA | 2.2 | Fang et al., 2021 |
| WEI | Rigid actuator with motor and reducer | IMU FSR | AOPO | Function | 4.8 | Yang et al., 2021 |
| HEBUT exosuit | Flexible actuator generate extension moment to hip by Bowden cable and assist hip flexion by the pulling belts | Force | FSM | Function | 7.5 | Chen et al., 2021 |
| XJTU exoskeleton | Rigid actuator with motor and reducer | IMU FSR | AO | Function | NA | Zhang et al., 2021 |
| UNC exoskeleton | Rigid actuator with motor and reducer | NA | FSM | HIL | NA | Tu et al., 2021 |
| SSSUP exosuit | A motor wraps up the left and right leg tendons | IMU | AO | NA | 2.2 | Tricomi et al., 2022 |
| U of U exoskeleton | A high-torque actuator. An electric motor located on the user’s legs transfers torque to the hip joint by gear stage, ball screw and nut, and spring. | IMU Encoder | FSM AO | Function | 2.7 | Ishmael et al., 2021, 2022 |
Abbreviations: AO, adaptive oscillators; AOPO, Adaptive Oscillator & Phase Oscillator; APO, Active Pelvis Orthosis; AWS, Augmented Walking Suit; CNN, Convolutional neural network; EMG, Electromyogram; FHAE, Flexible Hip Assistive Exoskeleton; FSM, finite state machine; FSR, force-sensitive resistor; GEMS, Gait Enhancing Mechatronic System; HIL, Human In the Loop; IMU, inertial measurement unit; NREL, “Not provided in references”; PGM, pneumatic gel muscle; QDD, quasi-direct drive; SAS, Stride Assistance System; SEA, serial elastic actuators; SIAT, Shenzhen Institute of Advanced Technology; SSSUP, Scuola Superiore di Studi Universitari e di Perfezionamento Sant’Anna; SMA, Stride Management Assist system; TBE, time-based estimation; WEI, Wearable Xian Jiao Tong University exoskeleton; XPED2, Not provided in references Exoskeleton Instrument; XJTU, Xian Jiao Tong University exoskeleton.