Sensors
If the leg is jumping, it has two degrees of freedom: The motion of the hip and the motion of the ankle which can move independently from each other. The position of both of them has to be measured and sent to the control unit. If the ankle is fixed on the floor (e.g. squat), only the hip can move up and down and the whole leg has only one degree of freedom.
Additionally, the motions in the actuation box have to be captured. The actuation box with the seri- al spring has also two degrees of freedom: The position of the carriages which the spring is fixed on. The position of the carriage on the motor side can be calculated using the motor angle, the position of the other carriage has to be measured.
The motor angle is measured by an encoder of the company “Maxon Motor GmbH”, which is shifted on the motor shaft. It uses the magneto resistive principal to capture the rotational position of the shaft.
<imgcaption image1|Sensors on the profile (not yet connected to the adapters)>
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The other three positions are measured by potentiometric position sensors of the company “Burster Präzisionsmesstechnik GmbH & Co. KG”. They are fixed to the aluminum profiles with screws and T-slot-nuts (Abb. 1). The connection to the carriages is realized by a ball joint on the end of the sensor and a screw, which is fixed to an adapter on the carriage. This screw is put through the hole of the ball joint.
The measuring range of the sensors is 250mm at the leg and 150mm at the spring. These ranges are big enough to realize the required motions. Because of the fastening of the sensors at the t-slot-nuts, they are easy to move or replace.