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| Learn More | Degrees of Freedom |
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| What is a Degree of Freedom? |
| An example using your arm. |
| More examples. |
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| What is a Degree of Freedom (DOF)? |
6 DOF Puma 760 |
The number of DOF that a manipulator possesses is the number of independent position variables that would have to be specified in order to locate all parts of the mechanism. In other words, it refers to the number of different ways in which a robot arm can move.
In the case of typical industrial robots, because a manipulator is usually an open kinematic chain, and because each joint position is usually defined with a single variable, the number of joints equals the number of degrees of freedom.
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| An example using your arm |
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You can use your own arm to get an idea of the degrees of freedom that a robot arm might have. Extend your arm straight out toward the horizon. Extend your index so it is pointing.
Keeping your arm straight, move it from the shoulder. You can move in three ways. Up-and-down movement is called pitch. Movement to the right and left is called yaw.
You can also rotate your whole arm as if you were using it as a screwdriver. This is called roll. Your shoulder has three degrees of freedom; pitch, yaw, and roll.
Now move your arm from the elbow only. This is rather hard to do without also moving your shoulder. Holding your shoulder in the same position constantly, you will see that your elbow joint has the equivalent of pitch in your shoulder joint. But that is all. Your elbow, therefore, has one degree of freedom.
Extend your arm toward horizon again. Now move only your wrist. Try to keep the arm above the wrist straight and motionless.
Your wrist can bend up and down, side to side, and it can also twist a little. Your lower arm has the same three degrees of freedom that your shoulder has (Most of the roll takes place all along your arm below the elbow).
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In total, your arm has seven degrees of freedom: three in the shoulder, one in the elbow, and three in the arm below the elbow. Three degrees of freedom are sufficient to bring the end of a robot arm to any point within its workspace, or work envelope, in three dimensions.
Thus, in theory, you might think that a robot should never need more than three degrees of freedom. But the extra possible motions, provided by multiple joints, give a robot arm versatility that it could not have with just three degrees of freedom.
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| More examples |
2 DOF |
7 DOF |
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