机器人手臂教程英文版_机器人手臂课程设计
机器人手臂教程英文版由刀豆文库小编整理，希望给你工作、学习、生活带来方便，猜你可能喜欢“机器人手臂课程设计”。
Degrees of Freedom Robot Workspace Mobile Manipulators Force Calculations Forward Kinematics Inverse Kinematics Motion Planning Velocity
Sensing
End Effector Design
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 chase 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 aignment I had when I took Robotic Manipulation back in college.My group programmed it to type the current time into the keyboard...(leon learned, don't crash robot arms into your keyboard at full speed while testing in front of your profeor)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 importantL1^2x * L2 * s2)/(x^2 + y^2))where c2 =(x^2 + y^2L2^2)/(2 * L1 * L2);and s2 = sqrt(1leaving the end effector to poibly swing wildly between those points.In the image below the end effector of the robot arm is moving from the blue point to the red point.In the top example, the end effector travels a straight line.This is the only poible motion this arm can perform to travel a straight line.In the bottom example, the arm is told to get to the red point as fast as poible.Given many different trajectories, the arm goes the method that allows the joints to rotate the fastest.Which method is better? There are many deciding factors.Usually you want straight lines when the object the arm moves is really heavy, as it requires the momentum change for movement(momentum = ma * velocity).But for maximum speed(perhaps the arm isn't carrying anything, or just light objects)you would want maximum joint speeds.Now suppose you want your robot arm to operate at a certain rotational velocity, how much torque would a joint need? First, lets go back to our FBD:
Now lets suppose you want joint J0 to rotate 180 degrees in under 2 seconds, what torque does the J0 motor need? Well, J0 is not affected by gravity, so all we need to consider is momentum and inertia.Putting this in equation form we get this: torque = moment_of_inertia * angular_acceleration breaking that equation into sub components we get: torque =(ma * distance^2)*(change_in_angular_velocity / change_in_time)and change_in_angular_velocity =(angular_velocity1)-(angular_velocity0)
angular_velocity = change_in_angle / change_in_time
Now auming at start time 0 that angular_velocity0 is zero, we get torque =(ma * distance^2)*(angular_velocity / change_in_time)where distance is defined as the distance from the rotation axis to the center of ma of the arm: center of ma of the arm = distance = 1/2 *(arm_length)(use arm ma)but you also need to account for the object your arm holds: center of ma of the object = distance = arm_length(use object ma)So then calculate torque for both the arm and then again for the object, then add the two torques together for the total: torque(of_object)+ torque(of_arm)= torque(for_motor)
And of course, if J0 was additionally affected by gravity, add the torque required to lift the arm to the torque required to reach the velocity you need.To avoid doing this by hand, just use the robot arm calculator.But it gets harder...the above equation is for rotational motion and not for straight line motions.Look up something called a Jacobian if you enjoy mathematical pain =P Another Video!
In order to better understand robot arm dynamics, we had a robot arm bowling competition using the same DENSO 6DOF robot arms as in the clocks video.Each team programs an arm to do two tasks: o o Try to place all three of its pegs in the opponents' goal Block opponent pegs from going in your own goal Enjoy!(notice the different arm trajectories)Arm Sagging
Arm sagging is a common affliction of badly designed robot arms.This is when an arm is too long and heavy, bending when outwardly stretched.When designing your arm, make sure the arm is reinforced and lightweight.Do a finite element analysis to determine bending deflection/stre such as I did on my ERP robot: Keep the heaviest components, such as motors, as close to the robot arm base as poible.It might be a good idea for the middle arm joint to be chain/belt driven by a motor located at the base(to keep the heavy motor on the base and off the arm).The sagging problem is even worse when the arm wobbles between stop-start motions.The solve this, implement a PID controller so as to slow the arm down before it makes a full stop.Sensing
Most robot arms only have internal sensors, such asencoders.But for good reasons you may want to add additional sensors, such as video, touch, haptic, etc.A robot arm without video sensing is like an artist painting with his eyes closed.Using basic visual feedback algorithms, a robot arm could go from point to point on its own without a list of preprogrammed positions.Giving the arm a red ball, it could actually reach for it(visual tracking and servoing).If the arm can locate a position in X-Y space of an image, it could then direct the end effector to go to that same X-Y location(by using inverse kinematics).If you are interested in learning more about the vision aspect of visual servoing, please read the Computer Vision Tutorials for more information.Haptic sensing is a little different in that there is a human in the loop.The human controls the robot arm movements remotely.This could be done by wearing a special glove, or by operating a miniature model with position sensors.Robotic arms for amputees are doing a form of haptic sensing.Also to note, some robot arms have feed back sensors(such as touch)that gets directed back to the human(vibrating the glove, locking model joints, etc.).Tactile sensing(sensing by touch)usually involves force feedback sensors and current sensors.These sensors detect collisions by detecting unexpected force/current spikes, meaning a collision has occurred.A robot end effector can detect a succeful grasp, and not grasp too tight or too lightly, just by measuring force.Another method would be to use current limitersperhaps even identify the object by its weight.Try this.Close your eyes, and put both of your hands in your lap.Now keeping your eyes closed, move your hand slowly to reach for your computer mouse.Do it！！You will see why soon...Now what will happen is that your hand will partially mi, but at least one of your fingers will touch the mouse.After that finger touches, your hand will suddenly re-adjust its position because it now knows exactly where that mouse is.This is the benefit of tactile sensing-no precision encoders required for perfect contact!
End Effector Design
In the future I will write a separate tutorial on how to design robot grippers, as it will require many more pages of material.In the meantime, you might be interested in reading the tutorial for calculating friction and force for robot end effectors.I also went in to some detail describing my robot arm card dealing gripper.Anyway, I hope you have enjoyed this robot arm tutorial!
