Assistive single-joint lower-limb exoskeletons have shown potential clinical benefits in patients with gait deficiencies. Torque-controlled exoskeletons, unlike position-controlled exoskeletons, do not restrict voluntary movements, allowing for safer interaction with the user. A torque-controlled hip flexion/extension exoskeleton intended for individuals with cerebral palsy is presented in this paper. The overarching research objective is to mitigate hip extension deficit and excessive hip flexion observed in crouch gait and apparent equinus gait patterns, which may be achieved by providing an extension torque during the stance phase. We expound on the design of an exoskeleton capable of performing this task, including a detailed discussion of the design, torque control, and benchmarking of its actuators. The device features series elastic actuators with a low output impedance and individualized orthotics designed using algorithmic 3D modeling and manufactured using additive manufacturing technologies. The exoskeleton's mechanical structure, orthotics, control, user interface, and safety functions are presented. A performance evaluation was conducted through a trial on an unimpaired participant (174 cm, 74.5 kg). Up to 35 Nm of extension torque during stance could be achieved during walking on a treadmill with a stride time of 1.2 s. The participant was asked to simulate a crouched gait and experienced a lifting sensation at approximately 16 Nm of extension torque during stance, making it difficult to maintain the crouch.
