Kojiro, Robot dengan Otot
Kojiro is an advanced musculoskeletal humanoid robot under development at the University of Tokyo’s JSK Robotics Laboratory. Musculoskeletal means Kojiro can mimic human body in skeletonmuscles, and tendons work to generate motion. The designer goal is to build robots that are light and agile, capable of moving around and interacting with the physical world in the same way our flesh bodies do.
Unlike most humanoids robot where have articulated limbs and torsos powered by DC motors at the joints, with this system these robots have a good range of motion, typically hard and heavy but making collisions with humans and objects a big problem. Kojiro have another way to solve this problem. There is, Kojiro does use DC motors, but the motors pull cables attached to specific locations on the body, simulating how our muscles and tendons contract and relax. These tendon-muscle structures, Kojiro has about 100 of them, work together to give the robot some 60 degrees of freedom, or much more than could be achieved with motorized rotary joints.
In Kojiro, uses lightweight and high-performance and quite small DC brushless motors (16 millimeters [0.6 inches] in diameter and 66.4 mm [2.5 inches] in length) but can deliver a substantial 40 watts of output power.
Each motor unit has a rotary encoder, tension sensor, and current and temperature sensing circuit. A driver circuit board automatically adjusts the current fed to the motors based on temperature measurements. The results are transmitted to a computer and displayed on a control screen.
The main drawback of using a musculoskeletal system is that controlling the robot’s body is difficult. This kind of system has lots of nonlinearities and is hard to model precisely. To develop control algorithms for Kojiro, the JSK team is using an iterative learning process. They first attempt small moves and little by little tweak the control parameters until the robot can handle more complex movements.