Medical Engineering & Physics 34 (2012) 1448–1453 Contents lists available at SciVerse ScienceDirect Medical Engineering & Physics j o ur nal homep age : www.elsevier.com/locate/medengphy An intrinsically compliant robotic orthosis for treadmill training Shahid Hussain a,∗ , Sheng Quan Xie a , Prashant K. Jamwal a , John Parsons b a Department of Mechanical Engineering, The University of Auckland, Auckland, New Zealand b School of Nursing, The University of Auckland, Auckland, New Zealand a r t i c l e i n f o Article history: Received 3 November 2011 Received in revised form 29 December 2011 Accepted 7 February 2012 Keywords: Compliance Gait rehabilitation Treadmill training Pneumatic muscle actuators Robotic orthosis a b s t r a c t A new intrinsically compliant robotic orthosis powered by pneumatic muscle actuators (PMA) was devel- oped for treadmill training of neurologically impaired subjects. The robotic orthosis has hip and knee sagittal plane rotations actuated by antagonistic configuration of PMA. The orthosis has passive mecha- nisms to allow vertical and lateral translations of the trunk and a passive hip abduction/adduction joint. A foot lifter having a passive spring mechanism was used to ensure sufficient foot clearance during swing phase. A trajectory tracking controller was implemented to evaluate the performance of the robotic orthosis on a healthy subject. The results show that the robotic orthosis is able to perform the treadmill training task by providing sufficient torques to achieve physiological gait patterns and a realistic stepping experience. The orthosis is a new addition to the rapidly advancing field of robotic orthoses for treadmill training. © 2012 IPEM. Published by Elsevier Ltd. All rights reserved. 1. Introduction Robotic orthoses are gaining recognition among the rehabilita- tion engineering community for the treadmill training of subjects suffering from neurologic impairments such as stroke [1,2] and spinal cord injuries (SCI) [3–5]. These robotic orthoses relieve the physical therapist from the strenuous task of manual assistance and facilitates in delivering well-controlled repetitive and prolonged training sessions at a reduced cost. The physical therapist’s role is limited to supervision. The subjectivity of manual training process is eliminated by providing measurement of interaction forces and limb movements to assess the quantitative level of motor function recovery. The first modern automated treadmill based gait training orthosis, LOKOMAT had been developed in late 1990s and is commercially available [6]. Several other research prototypes of robotic gait training orthoses namely; active leg exoskeleton (ALEX) [2], ambulation-assisting robotic tool for human rehabilitation (ARTHUR) [7], Lower extremity powered exoskeleton (LOPES) [8], pelvic assist manipulator (PAM) and pneumatically operated gait orthosis (POGO) [9] had also been developed during the last decade. Actuators hold a paramount importance in the design and func- tioning of these robotic orthoses. Two approaches have been used in actuator placement for powering the robotic orthoses [10]. In one of the approaches, the actuators have been placed on a remote station and the actuation has been transferred to the orthosis joints ∗ Corresponding author. Tel.: +64 9 3737599x87555; fax: +64 9 3737479. E-mail address: shus045@aucklanduni.ac.nz (S. Hussain). via cables, rigid linkages [8,11] and pneumatic or hydraulic systems [9]. LOPES [8], PAM [9] and the cable-driven locomotor training sys- tem [11] are the rehabilitation devices using this approach. In the second approach the actuators have been directly mounted on the orthosis frame. LOKOMAT [6] and ALEX [2] use this approach of actuator mounting. The benefit of the first approach is that there are no limita- tions on actuator weight and hence the power capacity of the actuators. Lack of precise control, inefficient transfer of power and non-durability of the actuation transfer mechanism (cables) are the drawbacks associated with this approach [10]. The main advantage of the second approach is the efficient transfer of power and a bet- ter alignment of orthosis joints with patient joints [10]. But the disadvantage is the use of geared electric motors which are either extremely heavy [10] or have high endpoint impedance (stiffness) [11]. The use of heavier electric motors and gear assembly increases the overall weight of the robotic orthosis which is not suitable for implementing advance control strategies such as impedance con- trol [8]. If light weight electric motors are used, the force and torque generation capabilities of the robotic orthosis are seriously compro- mised [10]. Also these high endpoint impedance electric motors are more suitable for industrial applications. Neurologically impaired patients often suffer from severe spasms. These stiff actuators may produce large forces in response to the undesirable motions pro- duced by spasms (position errors) [12,13]. As a result the patient may feel pain or discomfort. We believe that the second approach of directly mounting the actuators on the orthosis frame may become more beneficial if the limitations on the weight and the endpoint impedance of the actuators could be overcome. Also adding com- pliance to the actuation mechanism would help in absorbing large 1350-4533/$ – see front matter © 2012 IPEM. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.medengphy.2012.02.003