Application of Wearable Sensors in Actuation and Control of Powered Ankle Exoskeletons: A Comprehensive Review
Abstract
:1. Introduction
- General information including the exoskeleton purpose and target population, target limb side (bilateral or unilateral), degree of freedom (DoF), and assistance direction (dorsiflexion or plantar flexion or both), portability, and the total weight.
- Actuation principle and actuator type.
- Control hierarchy including high-level and low-level control schemes.
- Sensor system including human–machine and machine–machine sensors
2. Sensor Technologies Used in Control Hierarchy of the PAEs
- Robustness and reliability: the redundant data generated by multiple sensor units enables the system to provide information in case of partial failure.
- Extended spatial and temporal coverage: one sensor can look where others cannot and can perform a measurement while others cannot.
- Increased confidence: a measurement from one sensor is confirmed by measurements from other sensors.
- Reduced ambiguity and uncertainty: joint information reduces the set of ambiguous interpretations of the measured value.
- Robustness against interference: by increasing the dimensionality of the measurement (e. g., measuring the desired quantity with optical encoders and IMUs), the system becomes less vulnerable to interference.
- Improved resolution: when multiple independent measurements of the same property are fused, the resolution of the resulting value is better than for a single sensor measurement [46].
2.1. High-Level Control and Human–Machine Sensors
2.1.1. Phase-Based Control and Physical Sensors
2.1.2. Myoelectric-Based Control and Biosensors
2.2. Low-Level Control and Machine–Machine Sensors
Actuation Principle | Actuator Type | Portability | References |
---|---|---|---|
Pneumatic | Artificial Pneumatic Muscles (PAM) | Yes | [131,146,174,175,176] |
No | [11,38,49,50,62,63,88,89,90,91,92,93,95,96,97,98,99,132,133,134,135,142,179,190,191,192,193,194,195,196,197,198,199,200,201,203] | ||
Pneumatic Cylinders | Yes | [43,166,167,168,169,170,171] | |
Exosuit Pneumatic Source (Soft Fabric Actuator) | No | [156,232] | |
Soft Fiber Braided Bending Actuator | No | [211] | |
Electric | Brushed DC Motors | Yes | [115,172] |
No | [86,121] | ||
Brushless DC Motors | Yes | [37,39,40,42,57,65,66,76,77,78,79,80,81,82,83,84,100,101,102,111,112,113,117,118,122,123,127,157,158,159,160,178,184,185,186,187] | |
No | [64,103,104,105,106,107,108,109,110,116,124,125,129,143,147,148,149,150,151,161,162,163,164,165,210] | ||
Servo DC Motors | Yes | [74,75,87,119,120,144,145,177] | |
No | [141] | ||
Servo AC Motors | No | [53,58,68,69,70,71,72,73,180,181,182,183,202,204] | |
Stepper Motor | No | [189] | |
Permanent Magnetic Synchronous Motors | No | [85] | |
Electromechanical DC Voice Coil Actuator | No | [154,155] | |
Electrohydraulic Hybrid Drive System | Yes | [173] | |
No | [138,139,140] | ||
Electric Motors (Type Not Specified) | Yes | [56,114] | |
No | [41,126,128] | ||
Series Elastic | Brushed DC Motors | Yes | [234,235] |
No | [67] | ||
Brushless DC Motors | Yes | [130] | |
No | [10,54,55,59,60,61,136,152,153,188,207] | ||
Not Specified | [236] | ||
Servo DC Motors | No | [137] | |
Electric Motors (Type Not Specified) | Yes | [206] | |
No | [205] | ||
Dielectric Elastomer | Polyimide Fibers | Yes | [94] |
3. Towards Fully Autonomous Portable PAEs
Role of Wearable Sensors in Developing Autonomous Portable Ankle Exoskeletons
4. Conclusions
Supplementary Materials
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Fang et al., 2020 [37] (copyrights authorized by Elsevier) | Purpose: Assistive Device: Cerebral Palsy, Neuromuscular Impaired, and Parkinson Patients Bilateral: Yes DoF: 1 DoF Plantar Flexion Portability: Portable Weight: 1.85 kg–2.20 kg | High-Level Control Scheme: Phase-based Human-Machine Sensors: FSRs Low-Level Control Scheme: Adaptive PID Machine–Machine Sensors: Torque Sensors Actuation Mechanism: Brushless DC Motors |
Choi et al., 2020 [38] | Purpose: Assistive Device: Elderly Bilateral: No DoF: 2 DoF Plantar Flexion and Eversion/Inversion Portability: Tethered Weight: 2.14 kg | High-Level Control Scheme: Phase-based Human–Machine Sensors: FSR, Encoder Low-Level Control Scheme: Pulse Width Modulation (PWM) with Solenoid Valves Machine–Machine Sensors: Load Cell Actuation Mechanism: Pneumatic Muscle |
Bougrinat et al., 2019 [39] (copyrights authorized by Elsevier) | Purpose: General Augmentation Bilateral: No DoF: 1 DoF Plantar Flexion Portability: Portable Weight: 2.045 kg | High-Level Control Scheme: Phase-based Human–Machine Sensors: FSR, Low-Level Control Scheme: PID Machine–Machine Sensors: Load Cell, Current Sensor, Encoder Actuation Mechanism: Brushless DC Motors |
Guerro-Castellanos et al., 2018 [40] (copyrights authorized by Elsevier) | Purpose: Assistive Device: Drop Foot and Paretic Patients Bilateral: No DoF: 1 DoF Dorsiflexion/Plantar Flexion Portability: Portable Weight: 3.5 | High-Level Control Scheme: Phase-based Human–Machine Sensors: FSR, Encoder, IMU, EMG Low-Level Control Scheme: Adaptive (active disturbance rejection) Actuation Mechanism: Brushless DC Motors |
Sloot et al., 2018 [41] (copyrights authorized by Elsevier) | Purpose: General Augmentation Bilateral: Yes DoF: 1 DoF Plantar Flexion Portability: Tethered Weight: 3.8 kg | High-Level Control Scheme: Phase-based Human–Machine Sensors: Angle Sensor, IMU Low-Level Control Scheme: Simple position control Machine–Machine Sensors: Load Cell, Actuation Mechanism: Brushless DC Motor |
Emmens et al., 2018 [42] | Purpose: Assistive Device: Patients with Spinal Cord Injuries Bilateral: Yes DoF: 1 DoF Dorsiflexion/Plantar Flexion Portability: Portable Weight: 6.7 kg | High-Level Control Scheme: Reflex Model-based Human–Machine Sensors: FSR, Encoder, EMG Low-Level Control Scheme: P, PI Machine–Machine Sensors: Encoder Actuation Mechanism: Brushless DC Motor |
Boes et al., 2018 [43] (copyrights authorized by Elsevier) | Purpose: Assistive Device: Multiple Sclerosis Patients Bilateral: No DoF: 1 DoF Dorsiflexion/Plantar Flexion Portability: Portable Weight: 3.1 kg | High-Level Control Scheme: Phase-based Human–Machine Sensors: FSR, Encoder Low-Level Control Scheme: Proportional Pressure Regulators with Solenoid Valves Machine–Machine Sensors: Pressure Sensors Actuation Mechanism: Pneumatic Cylinders |
High-Level Control Scheme | Reference |
---|---|
Phase-based | [10,37,38,39,40,41,43,49,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,123,124,125,126,127,128,129,130,131,132,133,134,135,136,137,138,139,140,141,142,143,144,145,146,147,148,149,150,151,152,153,154,155,156,157,158,159,160,161,162,163,164,165,166,167,168,169,170,171,172,173,174,175,176,177,178,179] |
Impedance-based | [74,75,102,136,161,162,163,164,165,180] |
Metabolic-rate-based | [70,96,132,181,182] |
Reflex-model-based | [68,183,184,185,186,187,188] |
Proportional-myoelectric-based | [11,49,68,89,189,190,191,192,193,194,195,196,197,198,199,200,201] |
Adaptive gain proportional-myoelectric-based | [133,134,135,202,203,204,205] |
Myoelectric neuromechanical-model-based | [206,207] |
Push-button | [49,50] |
Measured Parameter | Sensor | References |
---|---|---|
Gait events | FSR | [37,38,39,40,43,56,57,59,60,61,62,63,64,65,67,76,77,78,79,80,81,82,83,84,85,87,94,107,116,117,118,119,120,141,142,143,145,147,148,149,150,151,152,153,156,159,160,166,167,168,170,171,173,174,175,177,178,184,186,187,189] |
Footswitch | [10,49,58,69,72,73,88,89,91,92,93,97,98,99,111,113,122,139,154,155,163,164,165,181,198,199,202] | |
IMU | [57,66,74,75,102,158,170] | |
Gyroscope | [112] | |
Piezoresistive sensor | [109,110] | |
Ankle joint angle | Encoder | [38,40,42,58,62,63,64,68,69,72,73,85,86,100,103,104,106,108,109,110,117,118,138,139,142,149,150,151,159,160,161,162,165,173,178,181,185,186,187,188,202,206,207,210], |
Potentiometer | [10,43,59,101,102,114,143,147,148,154,155,166,167,170,171] | |
Gyroscope | [172] | |
Linear displacement sensor | [97,98,99] | |
IMU | [64,127,152,211] | |
Goniometer | [180,183] | |
Attitude sensor | [116] | |
Custom strain sensor combined with IMU | [174,175] | |
Strain sensor | [87] | |
Knee joint angle | IMU | [206,207] |
Strain sensor | [87] | |
Absolute shank angle | IMU | [40,85,87,117,118,159,160,177] |
Orientation of shank, thigh, and trunk | IMU | [42] |
Inclinometer | [82] | |
Angular velocity | Gyroscope | [123,124,125,126,128,129,150,151,157,172] |
IMU | [114,119,120] | |
Translational acceleration of wearer | IMU | [40,117,118,119,120,159,160] |
Foot tilting | Accelerometer | [141] |
IMU | [119,120] | |
Walking speed | Speed encoder | [204] |
Ground reaction force | Force sensor | [10,136] |
FSR | [101,117,131] | |
Muscle activity | EMG | [11,40,49,68,89,116,117,133,134,135,181,185,186,190,191,192,193,194,196,197,198,199,200,201,202,203,204,205,206,207] |
Anatomical ankle generated torque | Strain gauges | [101,102] |
Exoskeleton frame–user interaction forces | Force sensor | [136] |
Respirometry | Metabolic mask | [70,96,132] |
Sensor | Specific Sensor Details | Measurement | Location | Reference |
---|---|---|---|---|
IMU | IMU (gyroscope and accelerometer) | Ankle joint angle | Foot and calf | [56] |
WT901C485, WitMotion, Shenzhen, China | Gait cycle | Shoe | [57] | |
EBIMU-9DoFV5, E2BOX Inc., Shanghai, China | Ankle joint angle | Shin and thigh parts of the exoskeleton | [64] | |
6-DoF IMU, 100Hz | Gait phase | Shank | [66] | |
BNO055 (Bosch, Germany) | Gait phase | Foot | [74,75] | |
3DM-GX4-25-RS232-SK1, LORD MicroStrain, Inc., Williston, VT, USA | Absolute shank angle | Main structure | [85] | |
MW-AHRS, NTRexLAB | Absolute shank angle | Shank | [87] | |
EBIMU-9DoFV4, E2BOX | Shank angle in sagittal plane | Medial shank | [177] | |
3 × Xsens (Xsens Technologies B.V., Enschede, The Netherlands) | Orientation of the shank, thigh, and trunk | Shank, thigh, and trunk | [42] | |
MPU6050 | Ankle joint angle | Foot | [211] | |
Not specified | Gait phase segmentation | Foot | [102] | |
IMU (Shimmer Inc., Dublin, Ireland ) | Angular velocity | Shank | [114] | |
SN-IMU5D-LC, Cytron, Simpang Ampat, Malaysia | Shank’s angular velocity in the sagittal plane and accelerations along the y and z axes. | Mechanical structure, near shank | [158] | |
2 × Xsens (Xsens Technologies B.V., Enschede, The Netherlands) | #1: Angle between the shank and the vertical axis #2: Translational acceleration of the wearer along the three axes. | #1 Shank #2 Foot | [40,117,118,159,160] | |
Mpu6050 6-axis MotionTrackingTM device, InvenSense, San Jose, CA, USA | Leg linear acceleration | Leg brace | [119,120] | |
MTi-3, (Xsens Technologies B.V., Enschede, The Netherlands) | Foot angle and angular velocity | Lateral side of the shoe | [127] | |
Link, Xsens, The Netherlands | Knee joint angle | Not specified | [206,207] | |
XSens MTi-28A53G35, (XSens Technologies. Enschede, The Netherlands) | Orientation and position of the exoskeleton | Medial side of the exoskeleton | [170] | |
SEN-09623, 9DoF Razor IMU, Sparkfun Electronics, Boulder, CO 80301, USA. | Orientation of lower leg and foot | Foot and lower leg | [174,175] | |
IMU (Sparkfun Electronics, Boulder, CO 80301, USA, with a gyroscope ADXRS610 and two accelerometers ADXL320, from Analog Devices) | Absolute position of the exoskeleton | Not specified | [152] | |
Gyroscope | Gyroscope | Shank angular velocity to identify heel contact | Not specified | [157] |
Single axis Gyroscope | Gait phase | On the shin | [112] | |
2 × Single axis Gyroscope (LY3100ALH, STMicroelectronics, Geneva, Switzerland) | Sagittal angular velocity of the shank and foot | One at the top of the mid-foot and the other at the anterior side of the shank | [123,125,129] | |
LY3100ALH, STMicroelectronics-single axis | Angular motion of the foot for gait segmentation | Top of the mid-foot | [124] | |
Sparkfun, NIWOT, CO, USA | Angular motion of the foot for gait segmentation | Integrated in the shoe | [126,128] | |
2 × Gyroscopes | Sagittal angular motion and velocity of the foot for gait segmentation | Not specified | [172] | |
Rate gyro | Angular velocity of shank | Not specified | [150,151] | |
Accelerometer | Tilt sensor | Tilt of foot | Not specified | [141] |
Attitude sensor | 2 × JY901 attitude sensors | Ankle joint angle | Parallel to the lever and shank | [116] |
angular | Ankle joint angle and angular velocity | Ankle joint | [113] | |
Foot pressure sensors | 3 × Membrane pressure sensors | Plantar pressure distribution for gait cycle detection | Integrated insole | [56] |
Insole-shaped foot pressure sensors (RX-ES39, Roxi Technology, Jiangsu, China) | Identify the gait state using pressure of three parts, i.e., forefoot, toe, and heel | Shoes | [57] | |
4 × FSR (MA-152, Motion Lab System Inc., Baton Rouge, LA, USA) | Ground contact, gait phase | Heel, hallux, first metatarsal head, and fifth metatarsal base | [59,60,61] | |
FSR sensor | Gait phase | Heel and big toe | [38,62,63] | |
3 × FSR sensors | Gait phase | Toe, heel, and medial of the insole | [64] | |
2 × FSR (FlexiForce A401, Tekscan, Boston, MA, USA) | Gait phase | Heel and the metatarsal bone | [65,184] | |
FSR sensor | Gait cycle | Under the arch support of the shoe | [67] | |
2 × FSR sensor | Gait phase | Under the ball and heel of the foot | [76,77,78,79,81,82,84] | |
2 × FSR (FlexiForce A201, Tekscan, Inc., Boston, MA, USA) | Ground reaction force | Under forefoot | [37,80,83] | |
2 × FSR (FlexiForce A301, Tekscan, Inc., South Boston, MA, USA) | Gait phase | Embedded into the insole | [85,189] | |
Toe contact sensor like pressure switch or force-sensing resistor | Gait timing | Not specified | [94] | |
3 × FSR (FlexiForce, Tekscan, Boston, MA, USA) | Ground contact of each foot | Insole | [87] | |
Custom-designed FSR sole | Gait phase | Beneath the foot brace | [177] | |
FSR (Interlink 406, Adafruit, New York, NY, USA) | Gait phase | The user’s shoe at the anterior and posterior ends of the shoe insoles | [156] | |
FSR-151AS pressure sensor (IEE, Contern, Luxembourg) | Heel strike | Heel | [178,186,187] | |
2 × FSR sensors | Ground reaction force | Heel and toe | [101] | |
FSR (SEN-09376 Antratek used with Phidgets Voltage Divider 1121) | Initiation of new step | Heel | [107] | |
IMS009-C7.5 (FSR) | Heel strike | Heel | [116] | |
3 × FSR in a force sensitive resistor matrix (FSRM)—(Tekscan, Inc., Boston, MA, USA) | Distribution of ground reaction force | Heel, hallux, fifth metatarsal phalange joints | [40,117,118,159,160] | |
FSR | Heel strike | Not specified | [39] | |
2 × FSR-402 (Interlink Electronics Inc., Camarillo, CA, USA) | Foot loading pattern as an on/off switch. | Forefoot and heel | [119,120] | |
4 × FSR-402 (Interlink Electronics Inc., Camarillo, CA, USA) | Ground reaction force | Below the shoe insoles at the heels and toes | [131] | |
2 × FSR-402, 0.5 in circle; (Interlink Electronics Inc., Camarillo, CA, USA) | Gait phase | Heel and metatarsal heads | [43,166,167,168,170,171] | |
2 × FSR | Gait phase | Toe and heel | [141] | |
4 × FSR (FlexiForce-A201-25lb, Tekscan Inc., Boston, MA 02127, USA) | Gait phase | Embedded in a shoe insole | [174,175] | |
Sparkfun SEN-09375) | Gait phase | Heel of the plate | [142] | |
FSR | Heel and toe contact | In the shoes | [143] | |
3 × FSR (FlexiForce-A201-25lb, Tekscan Inc., Boston, MA 02127, USA) | Ground reaction force | Heel, lower forefoot, and big toe | [145] | |
FSR | Heel strike | Heel | [146,147,148,149,150,151] | |
3 × FSR | Gait phase | Under heel, middle, and front part of the shoe | [152] | |
4 × FSR | Gait phase | Flexible insole | [153] | |
Force sensor | Ultraflex system—with 6 capacitive force transducers 25 mm square and 3 mm thick | Ground reaction force | Bottom of the exoskeleton, two sensors beneath the heel and four beneath the forefoot region. | [10] |
2 × Force sensors | Interaction forces—the ground reaction forces during the contact of robotic device with the ground and other force sensors measure the interaction forces between the shank of the user and the robotic device. | Not specified | [136] | |
GRF sensing system consisting of two force sensors | Gait phase | Integrated into shoe | [173] | |
Footswitch | McMaster-Carr, Aurora, OH, USA | Heel strike | In the heel of the shoe | [58,69,72,73,181,202] |
Footswitch | Foot contact | Not specified | [49] | |
Footswitch | Foot contact | Under left forefoot inside the shoe | [88] | |
Footswitch (B&L Engineering, Santa Ana, CA, USA) | Foot contact | Inside shoe | [89,199] | |
IP67, Herga Electric, Suffolk, UK | Foot contact | Heel | [91,92] | |
Multimec 5E/5G, Mec, Ballerup, Denmark | Foot contact | In the heel of the shoe | [93,97,98,99] | |
Footswitch, model MA-153 | Heel strike | In the heel of a shoe worn with the orthosis | [10] | |
FSW (B&L Engineering, Santa Ana, CA, USA) | Heel and toe contact | Not specified | [111,113] | |
B&L Engineering, Santa Ana, CA, USA | Heel strike | Under foot | [122] | |
Footswitch (B&L Engineering, Santa Ana, CA, USA) with 4 individual footswitches | Gait phase | Inside shoe—at the heel, forefoot, medial, and lateral zones at the level of metatarsals. | [163,164,165] | |
Pressure sensor (footswitch) | Heel strike moment and stride length | Under the shoe | [139] | |
2 × Tactile Arrays | Position of orthosis | Incorporated in the foot part of the exoskeleton and in the insole of the healthy leg | [154,155] | |
Potentiometer | Rotary potentiometer | Ankle joint angle | Attached to the hinged ankle joint of the exoskeleton | [59,60,61] |
Precision potentiometer (resolution of 0.5°) | Ankle joint angle | Exoskeleton ankle joint | [101,102] | |
Bourns 6637S-1-502 5-k rotary potentiometer | Ankle joint angle | Not specified | [10] | |
Motorized linear potentiometer | Ankle joint angle | Integrated in wearable ankle robot | [114] | |
Rotary potentiometer 53 Series, Honeywell, Golden Valley, CA, USA). | Ankle joint angle | Exoskeleton ankle joint | [43,166,167,170,171] | |
Linear potentiometer | Ankle joint angle | Exoskeleton ankle joint | [143,148] | |
linear and an angular potentiometer | Ankle motion | Not specified | [147] | |
Rotary potentiometer | Ankle joint angle | Exoskeleton ankle joint | [154,155] | |
Encoder | Optical encoder (E8P; US Digital, Vancouver, WA, USA) | Ankle joint angle | Exoskeleton ankle joint | [58] |
2 × Absolute encoders (AMT203-V, CUI Inc., Tualatin, OR, USA) | Ankle joint angle | Exoskeleton joints corresponding to the talocrural and subtalar joints | [38,62,63,64] | |
Digital optical encoder | Ankle joint angle | Exoskeleton ankle joint | [68] | |
E4P and E5(US Digital Corp., Vancouver, WA, USA), for alpha and beta exoskeleton | Ankle joint angle | Exoskeleton ankle joint | [69] | |
Absolute magnetic encoder (MAE3, US Digital, Vancouver, WA, USA) | Ankle joint angle | Lateral side of each exoskeleton’s ankle joint | [73,202] | |
Digital optical encoders (E5, US Digital, Vancouver, WA, USA) | Ankle joint angle | Exoskeleton joint shaft | [72,181] | |
Angular sensor, PandAuto P3022, Mexico, Mexico | Absolute angle of Link 1 in exoskeleton | Exoskeleton | [86] | |
Optical incremental encoder (2048 CPR, E6-2048-250-IE-S-H-D-3, US Digital, Inc.) | Ankle joint angle | Exoskeleton ankle joint | [85] | |
RMB20IC13BC SSI-encoder (RLS-Renishaw, Ljubljana, Slovenia) | Ankle joint angle | Exoskeleton ankle joint | [42,100,178,185,186,187] | |
Incremental optical encoder (US Digital HUBDISK-2-2000-625-IE, module EM1-2-2000-I, DI/O type, 5 pins, 5V) | Ankle joint angle | Exoskeleton ankle joint | [103,104,106,210] | |
Joint encoder (2000 CPT, HEDS-5600, Broadcom, San Jose, CA, USA), quadrature encoder-70 | Ankle joint angle | Lateral 3D-printed mount on exoskeleton ankle joint | [108,109,110] | |
Encoder E2 | Ankle joint angle | Exoskeleton ankle joint | [188] | |
Incremental encoder | Ankle joint angle | Exoskeleton ankle joint | [40,117,118,159,160] | |
linear incremental encoders (Renishaw, Chicago, IL, USA) | Ankle joint angle | Traction drive | [161,162,165] | |
Optical 3 phase 4000 CPR | Ankle joint angle | Exoskeleton ankle joint | [131] | |
Absolute rotary encoder 20 b Aksim, RLS (Renishaw), Kemnda, Slovenia). | Ankle joint angle | Exoskeleton ankle joint | [206,207] | |
Optical encoder (US Digital Inc.) | Ankle joint angle | Exoskeleton ankle joint | [138,139] | |
Magnetic encoder (AN25-analog, KD Mechatech Co., Korea) | Ankle joint angle | Exoskeleton ankle joint | [173] | |
Rotary encoder | Foot rotation | Base of shank | [142] | |
Absolute angular encoder | Ankle joint angle | Exoskeleton ankle joint | [149,150,151] | |
Goniometer | Goniometer (5 kHz, 250 Hz Biometrics, Newport, UK) | Ankle joint angle | Exoskeleton ankle joint | [180] |
Goniometers (500 Hz, Biometrics, Newport, UK) | Ankle joint angle | Exoskeleton ankle joint | [183] | |
Linear displacement sensor | 100 Hz; SLS130, Penny & Giles, Christchurch, Newport, UK | Ankle joint angle | Foot and shank sections of the exoskeletons | [97,98,99] |
Strain sensor | Soft strain sensor | Ankle and knee joint angle | Knee and the ankle joints | [87] |
4 × strain gauges connected to a full Wheatstone bridge | Human–exoskeleton interaction torque | On the exoskeleton frame, near the ankle joint | [101,102] | |
4 × custom-built strain sensors | Ankle joint angle | Dorsal and medial side of the ankle | [174,175] | |
Piezoresistive sensor | 3 × Piezoresistive sensors | Gait phase | Foot section of the exoskeleton, underneath the calcaneus, the first metatarsal head, and the hallux. | [109] |
Piezoresistive sensor | Heel strike | Underneath the calcaneus | [110] | |
EMG | Surface electrodes, high-pass filtered at 20 Hz, rectified, low-pass filtered at 6 Hz | Muscle activity | Gastrocnemius muscle | [68] |
2 × Wired, bipolar electrodes (Bagnoli Desktop System, Delsys Inc., Boston, MA, USA) | Muscle activity | Medial and lateral aspects of the soleus | [202] | |
Wireless EMG system (Bagnoli, Delsys, MA, USA) | Muscle activity of four lower-leg muscles on the exoskeleton side | Medial gastrocnemius, lateral gastrocnemius, soleus, and tibialis anterior | [181] | |
1200 Hz, TeleMyo, Noraxon USA, Scottsdale, AZ, USA | Muscle activity | Soleus and tibialis anterior | [11] | |
1200 Hz, Konigsberg Instruments, Inc., Pasadena, CA, USA | Muscle activity | Soleus, medial gastrocnemius, tibialis anterior | [49,89,190,191,192,193,194,196,197,198,199,200,203] | |
Surface EMG (960 Hz SX230, Biometrics, Newport, UK). | Muscle activity of the paretic side | Soleus | [201,204] | |
Surface EMG | Muscle activity | Tibialis anterior and soleus muscles | [185,186] | |
Not specified | Muscle activity | Tibialis anterior, gastrocnemius, soleus, and the rectus femoris | [116] | |
2 × Electromyography sensors (Delsys) | Muscle activity | Tibialis anterior and gastrocnemius | [117] | |
EMG surface electrodes-1000 Hz; SX230, Biometrics | Muscle activity | Soleus | [133,134,135] | |
AxonMaster 13E500, Ottobock, Germany | Muscle activity | Lower limb | [206,207] | |
Surface EMG | Muscle activity | Tibialis anterior, lateral gastrocnemius, medial gastrocnemius, peroneus longus, and soleus | [205] |
Low-Level Control Scheme | References | |
---|---|---|
Classical PID | PID [39,53,54,55,56,67,68,76,77,78,79,82,86,101,102,108,109,110,114,119,120,121,136,138,139,140,154,155] | |
P [100,106,107,113,146,172,178,185,186,187,204] | ||
PI [85,100,105,178,185,186,187] | ||
PD [10,57,65,66,69,70,71,72,73,81,137,147,148,149,150,151,152,153,161,162,163,164,165,180,181,202,206,207] | ||
Adaptive PID [37,64,80,83,84] | ||
Iterative Learning | [58,68,69,70,71,72,73,131,181,182,202] | |
Adaptive | [40,68,159,160,189] | |
Sliding Mode | [53] | |
Open-Loop Feed-Forward | [94,158,184,206,207] | |
Pneumatic Actuation Controls | On-Off Solenoid Valves | [146,156,166,167,170,171,173,174,175] |
Pulse Width Modulation (PWM) with Solenoid Valves | [38,62,63,141,173,188] | |
Proportional Pressure Regulators with Solenoid Valves | [11,43,49,50,88,89,90,91,92,93,95,96,97,98,99,132,133,134,135,142,168,169,190,191,192,193,194,195,196,197,198,199,200,201,203] |
Measured Parameter | Sensor |
---|---|
Cable/rope tension | Tension sensor [53,182] force sensor [57] load cell [39,58,69,108,109,110,122,123,124,125,126,127,128,129,180,183,204] strain gauge [72,113,181] |
Mechanical deflection | Potentiometer [10,55,67,108,110,137,146,153,176] encoder [206,207,236] |
Pressure | Pressure sensor [62,63,146,156,158,166,171,173,176,232] |
Pneumatic muscle force | Load cell [11,38,49,50,62,63,88,89,91,96,97,98,99,131,134,190,191,192,193,194,196,197,198,199,200,203] |
Real torque measured from actuator | Torque sensor [85] |
Reaction torque measured at the ankle | Torque sensor [37,76,77,78,79,80,81,82,83,84,104,105,106] linear potentiometer [234] strain gauges [68,69,73,202] |
Forces delivered by exoskeleton | Load cell [138,139] |
Motor current | Current sensor [39,85,161,162] |
Motor position/velocity | Encoder [39,55,57,59,67,68,72,108,110,111,112,113,115,116,121,141,143,147,148,149,150,151,161,162,165,172,180,181,188,206,207,235] Hall sensor and resolver [85] |
Cable position | Potentiometer [126] |
Motor stroke | Encoder [42,100,178,185,186,187] |
Slave cylinder stroke | Optical distance sensor [158] |
Actuator lever/link angles | Encoder [103,104,106,210] |
Sensor | Specific Sensor Details | Measurement | Location | Reference |
---|---|---|---|---|
Load cell | LC201 Series; OMEGA Engineering, Stamford, CT, USA | Cable tension | At the ankle | [58] |
Inline tensile load cell: DCE-2500N, LCM Systems, Newport, UK,250Hz LP Filter | Actuation force | Attached to the end effector moment arm (~ 10 cm) through a series elastic element | [180] | |
Load cells (500 Hz, LCM Systems Ltd., Newport, UK) | Cable tension | In series with the force transmission cables and series elastic element | [183] | |
Tension load cell (CDFS-200, BONGSHIN LOADCELL, Osan, Korea)—one with each pneumatic artificial muscle | Pneumatic muscle force | Attached at the end of the pneumatic muscle | [38,62,63] | |
LC201, OMEGA Engineering Inc., Stamford, CT, USA) | Bowden cable tension | Alpha exoskeleton, Bowden cable | [69] | |
Tension load cell-(LC8150-375-1K 0–100 lbs, 1200Hz, OMEGA Engineering, Stamford, CT, USA) | Pneumatic muscle force | Between the pneumatic muscle and the rod end | [11,49,50,88,89,96,190,191,192,193,194,196,197,198,199,200,203] | |
Load cell (W2, A.L. Design, Buffalo, NY, USA) | Tensile force of pneumatic muscle | Not specified | [91] | |
100 Hz; 210 Series, Richmond Industries Ltd., Reading, UK | Pneumatic muscle force | Connected between the orthoses and the pneumatic muscles | [97,98,99] | |
Two in-line load cells (LSB200, FUTEK Advanced Sensor Technology, Irving, CA, USA) | Actuation force | Posterior side of the calf, near the proximal part of the orthosis. | [108,109,110] | |
Inline tensile load cell (DCE-2500N, LCM Systems, Newport, UK) | Actuation force | Bowden cable | [204] | |
LFT-13B, Shenzhen Ligent Sensor Tech Co., Ltd., Shenzhen, China (inline load cell) | Force applied on the struts | Not specified | [39] | |
2 × Load cell—one cantilevered load cell (Phidgets 3135 50 kg Micro Load Cell), second load cell (LCM300, FUTEK Advanced Sensor Technology, Irving, CA, USA) | Cable force at the top of the Bowden cable and forces delivered to the wearer | First one in pulley module, second one at the ankle in series with the cable | [122] | |
LTH300, FUTEK Advanced Sensor Technology, Irving, CA, USA | Bowden cable force | In series with the Bowden cable and the calf wrap | [123,124,125,129] | |
LSB200, FUTEK Advanced Sensor Technology Irving, CA, USA | Assistive force transmitted to the hip joint via straps | Left side of exosuit in series with the two vertical straps and the waist belt | [124,129] | |
2 × LSB200, FUTEK Advanced Sensor Technology, Irving, CA, USA | Delivered force at the ankle—DF and PF forces generated by Bowden cable retractions | Integrated into the exosuit’s textile loops of the calf wrap | [126,127,128] | |
Not specified | Pneumatic muscle force | Between the NcPAM and the bottom plate | [131] | |
OMEGA Engineering, Stamford, Connecticut | Actuation kinetics | In series with actuator | [134] | |
Load cell (range +/− 220 N; Transducer Techniques Inc.) | Forces transmitted to wearer | At the extremity of the slave cylinder | [138,139] | |
Strain gauge | Not specified | Plantar flexion torque | On heel lever | [68,73] |
4 ×strain gauges (MMF003129, Micro Measurements, Wendell, NC, USA) in a Wheatstone-bridge | Torque | On ankle lever | [69,202] | |
Wheatstone bridge consisting of four strain gauges (KFH-6-350-C1-11L1M2R, OMEGA Engineering, Norwalk, CT, USA) | Assistive torque | End of titanium ankle lever | [72,181] | |
LCM200, FUTEK Advanced Sensor Technology, Inc., Irvine, CA, USA | Cable tension | On transmission cable | [113] | |
Encoder | Incremental encoder | Motor position and velocity | Motor | [55] |
AMT103-V, CUI Inc., OR, USA (2048 counts per revolution). | Motor position and velocity | Motor | [57] | |
Optical encoder (E5 Optical Encoder, US Digital, Vancouver, WA, USA) | Motor pulley velocity | Motor | [180] | |
Not specified | Motor position and velocity | Motor | [59,60,61] | |
Incremental encoder with 1024 count per turn | Motor position | Motor | [67] | |
Digital optical encoders | Motor position | Motor | [68] | |
Digital optical encoders (E5, US Digital, Vancouver, WA, USA) | Motor position | Motor shaft | [72,181] | |
Incremental encoder (SCH24-200-D-03-64-3-B, Scancon, Allerød, Danmark) | Motor stroke | Motor axis | [42,100,178,185,186,187] | |
Absolute magnetic encoder (AS5048A, SPI type, 6pins, 5V, a4-bit) | Torque angle/lever arm angle | In actuator | [103,104,106,210] | |
Motor-shaft encoder | Motor position and velocity | Motor | [108,110] | |
Encoder E1 | Motor position | Motor | [188] | |
500-Count quadrature incremental optical encoders (model: HEDL 5540, Maxon Motors, Sachseln, CH). | Motor position | Motor | [111,112] | |
14-Bit magnetic on-axis relative encoder (AS5047P and AS5047D, AMS AG, Premstaetten, AT) | Motor position | Motor | [113] | |
Encoder (ENX16 EASY 500IMP) | Motor position | In actuator module | [115,116] | |
Motor Encoder | Motor position and velocity | Motor | [39,143,147,148] | |
Quadrature encoders (2×195 RPM and 2×60 RPM HD premium planetary gearheads) | Motor position and velocity | Motor | [121] | |
Rotary encoder—Gurley R119 rotary encoders (Gurley, Troy, NY) | Commutate the motor | Mounted coaxially with the motors | [161,162,165] | |
Encoder FPC optical 3 phase 4000 CPR | Not specified | Inside the thrust bearing | [131] | |
Absolute angle Hall encoder (MHM, IC Haus, Germany) | Motor position | Motor | [206,207] | |
Angle encoder | Motor position and velocity | Motor | [235] | |
Absolute rotary encoder 20 b AksIM, RLS (Renishaw), Kemnda, Slovenia). | Spring deflection | Not specified | [206,207] | |
Encoder (5540 HEDL) | Motor position | Motor | [172] | |
2 × Rotary encoder and linear encoder | Spring deflection | In actuator | [236] | |
Encoder with servo motor | Actual position sensing of actuator | Motor | [141] | |
Digital incremental motor encoder | Determine position of lead screw | Not Specified | [149,150,151] | |
Hall sensors and resolver | Not specified | Motor position | Motor | [85] |
Potentiometer | Linear potentiometer | Spring deflection | Motor housing | [55] |
Linear potentiometer (50 mm travel length) | Spring deflection | Assembled to stainless steel pipe with a 3D-printed plastic housing. | [67] | |
Linear potentiometer | Spring deflection | Top of spring module | [10,108,110] | |
Linear potentiometer (P3 America Inc., San Diego, CA, USA) | Cable position | With actuator | [126] | |
Linear potentiometer | Joint torque | Mounted in parallel with series spring | [234] | |
Softpot linear position sensor | Transpose of spring | Not specified | [137] | |
Linear potentiometer | Deflection of links | Upper part of actuator link | [146,176] | |
Linear sliding potentiometer | Spring deflection | Fixed in the two-support platforms of the springs. | [153] | |
Tension sensor | Not specified | Cable tension | Bowden cable | [53] |
Not specified | Cable tension | At the end of Bowden cable | [182] | |
Pressure sensor | TST-20.0, TIVAL Sensors GmbH, Wuppertal, Germany | Pressure of pneumatic muscle | Pneumatic muscle | [62,63] |
ASDXAVX 100PGAA5, Honeywell Sensing and Productivity Solutions, Charlotte, NC, USA | Actuator pressure | Actuator | [156,232] | |
Pressure sensors (PX3AN1BH667PSAAX, Honeywell) | Measure the pressure in each hydraulic transmission | Not specified | [158] | |
Tethered pressure transducer: 4100 series, American Sensor Technology; Mt. Olive, NJ, USA) | Assistive torque-pressure in actuator | In actuator chamber | [166] | |
Pressure transducers (AST4000A00150P3B1000, 150 psig and AST4000A00100P3B0000, 100 psig, American Sensor Technologies, Inc, Mount Olive, NJ, USA) | Compressed CO2 pressure on both sides of the actuator | Actuator | [171] | |
5V G1/4 0–1.2 MPa, China | Senses the pressure in the cylinder chamber system | With the control hardware, attached to the waist of user | [173] | |
Not specified | Not specified | Upper end of actuator | [146,176] | |
Torque sensor | TRT-500, Transducer Techniques, Temecula, CA, USA | Reaction torque provided by the motors through the ankle pulley | Placed in line with each exoskeleton ankle joint/mounted on the insole | [37,76,77,78,79,80,81,82,83,84] |
Torque sensor (TPM 004+, Wittenstein, Inc., Igersheim, Germany) | Actuator torque output | Installed between the actuator case and the main structure | [85] | |
DRBK, ETH Messtechnik, 200 Nm, 0.0122 Nm resolution | Actuator torque output | Attached to test setup | [104,105,106] | |
Current sensor | Not specified | Active current | Motor | [85] |
Not specified | Motor current | Motor | [39] | |
Analog current sensor (Interactive Motion Technologies board employing TI/Burr-Brown 1NA117P) | Motor current to estimate motor torque | Motor | [161,162] | |
Distance sensor | Optical sensor (GP2Y0A51SK0F, Sharp) | Slave cylinder stroke | Not specified | [158] |
Force sensor | ZZ210-013, Zhizhan Measurement and Control, Shanghai, China | Cable force | Heel cable and forefoot cable | [57] |
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Kian, A.; Widanapathirana, G.; Joseph, A.M.; Lai, D.T.H.; Begg, R. Application of Wearable Sensors in Actuation and Control of Powered Ankle Exoskeletons: A Comprehensive Review. Sensors 2022, 22, 2244. https://doi.org/10.3390/s22062244
Kian A, Widanapathirana G, Joseph AM, Lai DTH, Begg R. Application of Wearable Sensors in Actuation and Control of Powered Ankle Exoskeletons: A Comprehensive Review. Sensors. 2022; 22(6):2244. https://doi.org/10.3390/s22062244
Chicago/Turabian StyleKian, Azadeh, Giwantha Widanapathirana, Anna M. Joseph, Daniel T. H. Lai, and Rezaul Begg. 2022. "Application of Wearable Sensors in Actuation and Control of Powered Ankle Exoskeletons: A Comprehensive Review" Sensors 22, no. 6: 2244. https://doi.org/10.3390/s22062244