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About this Robot Arm Tutorial
The robot arm is probably the most mathematically complex robot you could ever build. As such, this tutorial can't tell you everything you need to know. Instead, I will cut to the cha and talk about the bare minimum you need to know to build an effective robot arm. Enjoy!
To get you started, here is a video of a robot arm assignment I had when I took Robotic Manipulation back in college. My group programmed it to type the current time into the keyboard . . . (lesson learned, don't crash robot arms into your keyboard at full speed while testing in front of your professor)
You might be also interested in a robot arm I built that can shuffle, cut, and deal playing cards.
Degrees of Freedom (DOF)
The degrees of freedom, or DOF, is a very important term to understand. Each degree of
freedom is a joint on the arm, a place where it can bend or rotate or translate. You can typically identify the number of degrees of freedom by the number of actuators on the robot arm. Now this is very important - when building a robot arm you want as few degrees of freedom allowed for your application!!! Why? Becau each degree requires a motor, often an encoder, and exponentially complicated algorithms and cost.
Denavit-Hartenberg (DH) Convention
The Robot Arm Free Body Diagram (FBD)
The Denavit-Hartenberg (DH) Convention is the accepted method of drawing robot arms in FBD's. There are only two motions a joint could make: translate and rotate. There are only three axes this could happen on: x, y, and z (out of plane). Below I will show a few robot arms, and then draw a FBD next to it, to demonstrate the DOF relationships and symbols. Note that I did not count the DOF on the gripper (otherwi known as theend effector). The gripper is often complex with multiple DOF, so for simplicity it is treated as parate in basic robot arm design.
4 DOF Robot Arm, three are out of plane:
3 DOF Robot Arm, with a translation joint:
5 DOF Robot Arm:
Notice between each DOF there is a linkage of some particular length. Sometimes a joint can have multiple DOF in the same location. An example would be the human shoulder. The shoulder actually has three coincident DOF. If you were to mathematically reprent this, you would just say link length = 0.
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Also note that a DOF has its limitations, known as theconfiguration space大学生求职自荐信. Not all joints can swivel 360 degrees! A joint has some max angle restriction. For example, no human j
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oint can rotate more than about 200 degrees. Limitations could be from wire wrapping, actuator capabilities,多开头的成语 rvo max angle, etc. It is a good idea to label each link length and joint max angle on the FBD.
(image credit: Roble.info)
Your robot arm can also be on a mobile ba, adding additional DOF. If the wheeled robot can rotate, that is a rotation joint, if it can move forward, then that is a translational joint. This mobile manipulator robot is an example of a 1 DOF arm on a 2 DOF robot (3 DOF total).
Robot Workspace
The robot workspace (sometimes known as 高觉reachable space) is all places that the end effector (gripper) can reach. The workspace is dependent on the DOF angle/translation limitations, the arm link lengths, the angle at which something must be picked up at, etc. The workspace is highly dependent on the robot configuration.
Since there are many possible configurations for your robot arm, from now on we will only talk about the one shown below. I cho this 3 DOF configuration becau it is simple, yet isnt limiting in ability.
Now lets assume that all joints rotate a maximum of 180 degrees, becau most rvo motors cannot exceed that amount. To determine the workspace, trace all locations that the end effector can reach as in the image below.
Now rotating that by the ba joint another 180 degrees to get 3D, we have this workspace image. Remember that becau it us rvos, all joints are limited to a max of 180 degrees. This creates a workspace of a shelled mi-sphere (its a shape becau I said so).网络任务
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If you change the link lengths you can get very different sizes of workspaces, but this would be the general shape. Any location outside of this space is a location the arm cant reach. If there are objects in the way of the arm, the workspace can get even more complicated.
