Development of Waist Load Reduction Support Mechanism Utilizes the Principle of the Lever and the Force of the Spring

In this paper, a waist load reduction support mechanism utilizes the principle of the lever and the force of the spring was proposed and evaluated. There are many tasks that are required to unnatural postures and difficult hard work that mechanization is difficult in a wide range of fields such as care, logistics and agriculture. When carrying a load, the force acting on the upper body generates torque on the waist. Therefore, we decided that we needed to counteract the torque in order to reduce the burden on the waist. In this method, when lifting a heavy object, the proposed system transfers force to the hips, thighs, and chest. Like the principle of leverage, this mechanism maintains the balance of forces applied to the chest and legs with the waist as the fulcrum. In addition, the springs placed legs supports the rising motion. 100 N load lifting experiment shows that the rotational torque factor at the lower back was cancelled by the two pushing forces of the chest and the thigh. In the system, the rotational center was positioned on the lower back. We developed two types of the devices. (1) A device that cannot handle bending of the waist using only the principle of the lever. (2) A mechanism that freely responds to the bending of the waist by using the mechanism of the spring in addition to the principle of the lever. By using the spring mechanism, the bending angle range was extended to from 57.7 to 90.0 deg (=32.3 deg) in case of (2) comparing with (1) case from 68.4 to 75.0 deg (=6.6 deg). And the waist rotation moment value was reduced from about 8.7 Nm (without device) to -0.95 Nm (with the device) when 100 N load lifting experiment. The proposed system could cancel the effect on the rotation load of the waist by the three points - (1) the chest, (2) the thigh and (3) pushing force on the lower back (not rotation force).