Difference between revisions of "Types of joints"
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[[File:p560-joints.png|right|200px]] | [[File:p560-joints.png|right|200px]] | ||
[[File:privres-zaxes.png|left|180px]] | [[File:privres-zaxes.png|left|180px]] | ||
| − | There are two types of joints used for robotic arms, each with one single degree of freedom. In the following the abstractions shown in the figure on the left will be used. The first type is the '''prismatic joint''', that allows for translational movement along the joint axis. The displacement is described by the joint variable, for example <math>d</math> like in the figure. The second joint type is the '''revolute joint'''. A revolute joint allows for a rotation about the joint or rotation axis, respectively, and its joint parameter is the rotation angle, named <math>\theta</math> in the figure. | + | There are two types of joints used for robotic arms, each with one single degree of freedom. In the following the abstractions shown in the figure on the left will be used. The first type is the '''prismatic joint''', that allows for translational movement along the joint axis. The displacement is described by the joint variable, for example <math>d</math> like in the figure. The direction of the positive displacement is always indicated with a small arrow. The second joint type is the '''revolute joint'''. A revolute joint allows for a rotation about the joint or rotation axis, respectively, and its joint parameter is the rotation angle, named <math>\theta</math> in the figure. The arrow that could be seen in the figure indicates the rotation direction for positive angles. |
The Puma560 for example has three revolute joints, marked as <math>J_1</math>, <math>J_2</math> and <math>J_3</math> in the figure on the right. | The Puma560 for example has three revolute joints, marked as <math>J_1</math>, <math>J_2</math> and <math>J_3</math> in the figure on the right. | ||
[[File:right-hand-rotation.png|left|100px]] | [[File:right-hand-rotation.png|left|100px]] | ||
For the [[Assigning coordinate frames|assignment of coordinate frames]], the '''main joint axes''' are important. Like can be seen as blue arrows in the above figure on the left, the main axis <math>z_p</math> of a prismatic joint is the axis along which the displacement in positive direction is applied. For a revolute joint, the main axis <math>z_r</math> is the rotation axis. The direction of the rotation axis and so of the main axis is depending on the positive rotation direction. When you hold your right hand like shown on the right and point your thumb in the direction of the rotation axis, the four other fingers indicate the rotation direction for positive angles. So the right hand can be used to determine the direction of the main axis. In the figure on the left, the thumb of the right hand has to point upwards, so that the four fingers correspond to the direction of the arrow indicating the positive rotation direction. Thus the main axis is directed upwards as well. | For the [[Assigning coordinate frames|assignment of coordinate frames]], the '''main joint axes''' are important. Like can be seen as blue arrows in the above figure on the left, the main axis <math>z_p</math> of a prismatic joint is the axis along which the displacement in positive direction is applied. For a revolute joint, the main axis <math>z_r</math> is the rotation axis. The direction of the rotation axis and so of the main axis is depending on the positive rotation direction. When you hold your right hand like shown on the right and point your thumb in the direction of the rotation axis, the four other fingers indicate the rotation direction for positive angles. So the right hand can be used to determine the direction of the main axis. In the figure on the left, the thumb of the right hand has to point upwards, so that the four fingers correspond to the direction of the arrow indicating the positive rotation direction. Thus the main axis is directed upwards as well. | ||
Revision as of 10:54, 11 November 2015
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There are two types of joints used for robotic arms, each with one single degree of freedom. In the following the abstractions shown in the figure on the left will be used. The first type is the prismatic joint, that allows for translational movement along the joint axis. The displacement is described by the joint variable, for example 
like in the figure. The direction of the positive displacement is always indicated with a small arrow. The second joint type is the revolute joint. A revolute joint allows for a rotation about the joint or rotation axis, respectively, and its joint parameter is the rotation angle, named 
in the figure. The arrow that could be seen in the figure indicates the rotation direction for positive angles.
The Puma560 for example has three revolute joints, marked as 
, 
and 
in the figure on the right.
For the assignment of coordinate frames, the main joint axes are important. Like can be seen as blue arrows in the above figure on the left, the main axis 
of a prismatic joint is the axis along which the displacement in positive direction is applied. For a revolute joint, the main axis 
is the rotation axis. The direction of the rotation axis and so of the main axis is depending on the positive rotation direction. When you hold your right hand like shown on the right and point your thumb in the direction of the rotation axis, the four other fingers indicate the rotation direction for positive angles. So the right hand can be used to determine the direction of the main axis. In the figure on the left, the thumb of the right hand has to point upwards, so that the four fingers correspond to the direction of the arrow indicating the positive rotation direction. Thus the main axis is directed upwards as well.
