Fundamentos de robótica

Tipos de articulaciones.
Existen diferentes tipos de articulaciones. Las más utilizadas en robótica son las que se indican en la figura 3.

LABEL BALL
PLANAR
BARREL
ROTATION

Fig. 3 Tipos de articulaciones robóticas.
La articulación de rotación suministra un grado de libertad consistente en una rotación alrededor del eje de la articulación. Está articulación es, con diferencia, la másempleada.
En la articulación prismática el grado de libertad consiste en una traslación a lo largo del eje de la articulación.
En la articulación cilíndrica existen dos grados de libertad: una rotación y una traslación.
La articulación planar está caracterizada por el movimiento de desplazamiento en un plano, existiendo por lo tanto, dos grados de libertad.
Por último, la articulación esféricacombina tres giros en tres direcciones perpendiculares en el espacio.
Los grados de libertad son el número de parámetros independientes que fijan la situación del órgano terminal. El número de grados de libertad suele coincidir con el número de eslabones de la cadena cinemática.

 

ROBOT GEOMETRY
The study of robot kinematics, require a unified methodology to identify the variables of arobot's or manipulator's joints and links.
Co-ordinate Frames
Robotic kinematics depends on the use of right handed cartesian frames of reference. | |
Manipulator Geometry
A manipulator consists of two types of joints, connected by a link.
Link
A link is a solid mechanical structure which connects two joints. The main purpose of a link is to maintain a fixed relationship between thejoints at its ends. The last link of a manipulator has only one joint, located at the proximal end (the end closest to the base) of the link. At the distal end of this link (the end furthest away from the base) instead of a joint, there is usually a place to attach a gripper: a tool plate.
The common link configurations are shown below. Between the axes of the joints at the ends of any link there canbe two degrees of translation and two degrees of rotation. These degrees of freedom are called the link parameters.
Type 1 link
The simplest link has two parallel revolute joints with no twist between the axes; the axes of the joints are parallel. | |
Type 2 link
If one of the joints in a type 1 link is twisted about the centre line of the link by an angle , an extra degree of rotationis added. The twist angle is the angle that would exist between the joint axes if the joints were coincident, and it can be thought of as a rotation around the X axis. Thus, the type 2 link has one degree of translation and effectively two degrees of rotation. | |
Type 3 link

In this link, the second type of revolute joint in introduced. If joint n in the type 1 link is rotated 90o degreesabout the Y axis so that the Z axis is collinear with the centre line of the link, we have the link configurationa shown. The significant difference between this link and the previous two links is that the joint axes intersect, whereas in the type 1 and type 2 links they are parallel.
In summary
* The axes of the joints are always along the Z axis of the originating frame.
* The linkaxis is always along the X axis of the originating frame.
* The normal displacement between the two frame is given the symbol a.
* The twist angle between the two joint frames is given the symbol
Joints
Two types of joints are commonly found in robots: revolute joints, and prismatic joints. Unlike the joints in the human arm, the joints in a robot are normally restricted to one degreeof freedom, to simplify the mechanics, kinematics, and control of the manipulator.
Rotary or revolute joints
In the top two, the axis of the joint is coincident with the centre line of the link. In some designs it is normal to the distal link. This joint is often used as a waist joint.
In the bottom, the axis of the joint is normal to the link. One common use of this joint is as an elbow...