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Mechanical Constructions
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The new prototype of RobotaThe current prototype of the doll-shaped humanoid robot Robota is presented here. The use of the robot Robota as part of studies with disabled children sets a number of constraints on its design. In particular, it requires that the robot bears a human likeness both in its body features and in the kinematics of its motions. The current design consists in a 23 degrees of freedom upper body, including a 3 DOFs spine, two 7 DOFs arm, a 3 DOFs pair of eyes and a 3 DOFs neck. |
The prototype of eyesA prototype of a 3 DOFs pair of eyes has been developped. One DOF drives the horizontal rotation of the two eyes and the two other DOFs drive the vertical rotation of each eye. Thus, the robot can wink but not squint!In each eye, we have placed one ''mobile phone'' CMOS camera. The principal constraint in this project is the aesthetic of the robot. We use then real doll eyes that we modify to insert the cameras, by drilling a tiny hole through the pupil, making sure that the iris remains intact. The volume of the eyes is, however, too small to contain the electronic board (that proceeds to the digital conversion of the image). Thus, the sensor must be connected to the board through a flex cable in such a way that the cable is not impeding the movement of the eyes. |
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The prototype of armThe current prototype of arm is a 6 DOFs arm with a 1 DOF gripper. It is 26 centimeter long for 700gr. The motors were dimensioned so as to carry an external load of up to 200 gr. The different DOFs were designed to be reversible, in order to provide an interface for teaching the robot by demonstration.The first three degrees of freedom are placed in the shoulder. The three rotation axes cross at the same point. This implies that the elbow moves on a sphere. We have one DOF in the elbow and two DOFs in the wrist. The gripper is composed of 3 fingers actuated by one single DOF. To have an absolute measure of the position of each joint, we have placed potentiometers on each axis. We can, thus, measure the absolute position of the arm when the arm is switched on, and, hence, initialize the motor encoders without having to send the motors to the reset position. This ensures minimal risks when the robot interacts with children, by preventing any involuntary motion if the robot should reset itself. |
The prototype of neckFor the prototype of Robota's neck, we have 3 DOFs (lace, pitch and roll). These are placed in series, starting with lace, and, then pitch and roll. The system has been designed to support a load of 400gr, so that it could still drive the head of the robot in any position. Pitch and Roll are controlled by transmission through a set of cables and pulleys, while Lace is controlled by a direct drive from the motor. Using direct drive and cable transmission minimizes the chance of encountering backlash problems. |
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The prototype of spineThe current prototype of spine drives two DOFs for front-back and left-right bending respectively. The third DOF of the torso, supported by the spine, drives the horizontal rotation of the shoulders. The spine is about 200mm high for a diameter of 90mm. It weights about 1Kg and supports a load of 2Kg located at 80mm on the spine. This corresponds to the estimated mass of the current prototypes and position of the mass center of the two arms and the head.To obtain a smooth curvature along the spine, we have used a low pressure hydraulic system. Four pistons are placed at each level of the spine (there are four levels), two for each DOF. To move the spine, we have two motors placed in its base. Using a reduction gear, each motor transmits the movement to an endless screw that moves two pistons working as a pump. |
Videos
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| Movie of the Eyes (0:16) DivX, 1.2Mb |
Movie of the Arm (0:36) DivX, 3.0Mb |
Movie of the Neck (0:29) DivX, 2.4Mb |
Selected Publications
People involved in this project
