Sit-to-Stand and Stand-to-Sit Transfer Support for Complete Paraplegic Patients with Robot Suit HAL

Physical support of lower limbs during sit-to-stand and stand-to-sit transfers is important for an independent life of paraplegic patients. The purpose of this study is, therefore, to realize the control method of complete paraplegic patients during sit-to-stand and stand-to-sit transfers by using a 'robot suit HAL'. It is the most challenging issue because the HAL should start supporting the wearer's motions synchronizing his/her intention. Our proposed algorithm infers the intention based on a preliminary motion that is observed just before a desired motion so the patient could start the sit-to-stand or stand-to-sit transfers without any operation. When the HAL detects the intention to stand up and sit down, the HAL starts to support the wearer's weight and to control their body posture for stability during their transfer. The proposed algorithms embedded in the HAL were applied to a complete spinal cord injury patient in a clinical trial to confirm the effectiveness. The experimental results indicate that the proposed algorithms could support his sit-to-stand and stand-to-sit transfers safely and conveniently by keeping his stability and by reflecting his intentions. Consequently, we confirmed that the proposed method successfully supported the sit-to-stand and stand-to-sit transfers of the complete paraplegic patient with the HAL.     

Walking Pattern Generation for a Biped Walking Robot Using Convolution Sum

This paper describes a novel walking pattern generation method for a biped humanoid robot using a convolution sum. For a biped walking model, a single mass inverted pendulum model is generally used and the zero moment point (ZMP) equation is described by a decoupled linear differential equation. As a walking pattern generation method for the robot model, a novel method using a convolution sum is proposed in this paper. From the viewpoint of the linear system response, walking pattern generation can be regarded as a convolution of an arbitrary reference ZMP and the walking pattern for an impulse reference ZMP. For the calculation of convolution, the walking pattern for an impulse reference ZMP is first derived from the analytic walking pattern for a step reference ZMP. The convolution sum is then derived in two recursive forms, which can be applied online and offline, respectively. The proposed algorithm requires low computation power, since the walking pattern equation is composed of a recursive form. As the algorithm is expressed in analytic form, it is not necessary to solve optimization problems or calculate the fast Fourier transform, contrary to previous approaches. A computer simulation of walking demonstrates that the proposed algorithm yields excellent accuracy compared to the preview control method — one of the most highly regarded walking pattern generation methods. In addition, the application on the multi-point mass model is shown with the computer simulation.     

Ladder Climbing Method for the Limb Mechanism Robot ASTERISK

A ladder climbing method for the limb mechanism robot ASTERISK is proposed. This robot has six legs. The upper three legs hold on to the upper rung from both sides alternately, just like pinching it. The lower three legs hold on to the lower rung in the same way. Hence, the robot can take hold of the ladder stably. First, the robot releases the left upper and lower legs from the current rungs, and hangs them on the next rungs while supporting itself with the other four legs. Then, the mid two legs and the right two legs are moved to the next rungs in sequence. Finally, the robot lifts up its body using the six legs. Depending on the relative pose of the robot to the ladder, the robot automatically selects the legs that can support vertical and/or horizontal forces applied by the rungs. The robot then distributes its weight to the legs supporting the vertical force based on their force margins. The legs that cannot support forces are controlled to always touch the rungs slightly in order to pinch the rungs with the other legs. The advantages of the proposed gait and control method are verified by analysis of the leg workspace for generating the ladder climb gait, analysis of the range of force direction that the legs can support, analysis of the joint torques required for ladder climbing and an experiment on force distribution. Finally, the range of ladder pitch variation that ASTERISK can climb is clarified.