Understanding the reasons for which power-assist-lifted weight is 40% of actual weight: The preliminary studies

When a human manipulates an object with a power assist robot, the human feels a scaled-down effect of the load and the forces required to manipulate the object also reduce. We determined in our previous research that the power assist robot reduces the weight of the lifted object to 40% of its actual weight. However, the root cause of reduced heaviness of objects manipulated with power assist robots is still a mystery and the factors affecting the reduced heaviness are still unknown. The reasons for which the power-assist-lifted weight is 40% of the actual weight are still not understood. We think that the knowledge on the reasons and on the factors could be used to improve interactions between human users and power assist robots in various ways. This paper takes an initiative to understand the reasons for which the power-assist-lifted weight is 40% of the actual weight. Our strategy is to at first understand human´s weight perception, load forces and object´s motion features when lifting objects manually, and then to compare the findings to that when lifting objects with a power assist robot, and thus to try to find out the reasons. This paper reports the preliminary study results on weight perception, load forces and object motion features for lifting objects manually.