Evaluation of the passive exoskeleton

We performed a comprehensive evaluation of the new version of our passive SPEXOR exoskeleton, assessing the effect of wearing the exoskeleton on biomechanical loading of the spine, functionality, user satisfaction and self-efficacy. Recruiting employees from load-handling professions we tested participants with and without low back pain. We concluded that we reached beyond the state of the art by high versatility due to implementation of a clutch, higher support levels (50 Nm) and a limitation of lumbar flexion in static bending, leading to reduced loading of the spine during lifting and forward bend positions. In addition, we solved previously observed limitations of benchmarking devices, such as interference with tasks, discomfort and restricted range of motion. Both, healthy people and employees with low back pain can benefit from wearing the device. Design improvements that can still be considered are higher support to increase the effect on spine loading and higher user satisfaction by improving general comfort.

Design optimization for active spinal exoskeleton

Researchers at UHEI performed various optimization studies on the design of active spinal exoskeletons for the support of lifting motions which serve as an input for the upcoming work in the project.

  • For an exoskeleton model with rigid segments and motors at the hip and lumbar joints, we determined motions and corresponding human and exoskeleton torques that correspond to the smallest effort for the human, also respecting limits on the actuators.
  • For an exoskeleton model with rigid segments and motors with parallel springs at the hip and lumbar joints, we reconstructed recorded individual lifting motions of different subjects without exoskeletons. Various objective functions were evaluated that lead to different distributions of the dynamic efforts between the muscular torques of the human and the passive and active torques of the exoskeleton. Contact forces between the human and exoskeleton were limited to ergonomically reasonable values.
  • We also considered an exoskeleton model with a flexible beam element in the back and springs in the hip joint, corresponding to the current passive SPEXOR prototype. In addition to these passive elements, parallel actuators in the hip joints have been considered. The results show potential reductions in the human torques by the introduction of the active components.

Extending the spinal orthotic module with a passive self-aligning hip module

A misalignment compensation mechanism for the hip was developed to increase the comfort of the exoskeleton and to hinder movements as little as possible. A purely passive torque source at hip level generates the support needed to unload the lower back.

Passive spinal orthosis with viscoelastic element

Continuus carbon fiber beams which generate support and allow for a large range of motion are used as a back interface. Combined with the torque source at the hip, they generate the torque which reduces the strain on the lower back.

Biomechanical requirements for active version of spinal exoskeleton

We assessed full body kinematics and spine load components in natural lifting, to find kinematic and support pattern requirements for the SPEXOR actuated exoskeleton. Furthermore, using a benchmark actuated exoskeleton, we investigated how specific actuation control modes interact with subject behavior, and how this affects spine loading.

Biomechanical requirements for passive spinal exoskeleton are defined

We assessed to what extent a benchmark exoskeleton reduces spine loading and changes body kinematics during static trunk bending and during lifting. Additionally, we investigated how it affects perceived comfort, effort, performance, and metabolic energy consumption during functional activities such as walking and stair climbing. Based on these data, biomechanical requirements for the spexor passive exoskeleton were refined.

Monitoring system runs with full body model

The SPEXOR monitoring system is now linked with the full-body dynamical model providing insight into the musculoskeletal stress parameters. Further optimization for real-time processing and feedback are being addressed.

Controller for passive spinal exoskeleton

The controller for engagement and disengagement of the hip spring is developed. It is based on the probabilistic model of the human motion that classifies whether the user requires the support of the exoskeleton or the exoskeleton should remain disengaged to allow free motion.

Evaluation of the musculoskeletal stress monitoring system

We evaluated our optimized stress monitoring system, consisting of pressure insoles and inertial sensors, by comparing its performance to a laboratory grade system in a mock-up of realistic working conditions. Sensor outcomes and resultant low back load measures were compared between systems. The system was found to meet standards in accordance with the previously defined requirements.

Design optimization of passive spinal exoskeleton

In recent work UHEI led efforts towards the modeling of a passive spinal exoskeleton, and simulating the interaction between the human user and the exoskeleton (Millard et al. 2017, Manns et al. 2017, Harant et al. 2017). These results build upon earlier contributions of a dynamic whole body human model which is used as a basis for the exoskeleton design. We use a combined model of a human and a parametrized exoskeleton and setup optimal control problems to identify exoskeleton spring characteristics or motor torques for lifting motions. The motions simulated are either fitted to recorded data (collaboration with S2P and VUA), or generated as the solution of a minimization function. We also compute the forces and torques transmitted between the human and the exoskeleton. These are important first measures that will help support the exoskeleton and human-exoskeleton-interface design process.