Torque required to move robot arm (special linkage)

  • #1
slkmc wwojno
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TL;DR Summary
I need to calculate a torque required for uArm type of robot arm. Servos are at the base and 2 arms are controlled by system of linkage.
I need to calculate a torque required for uArm type of robot arm. Servos are at the base and 2 arms are controlled by system of linkage.
I suppose all necessary info will be given by CAD, like weight and mass of gravity,etc..
But How would I properly size the servos? Is it the same as in classic arm where each servo is at each joint? Please see provided CAD model in the Onshape Viewer.

Here is the CAD of the arm in question:

https://cad.onshape.com/documents/e...renderMode=0&uiState=655cc9f611f8d44e40ff0e2c

I changed the colours on the example assembly to make it more recognisable. Right servo is connected to the blue arm only. Left servo is connected to the purple arms. The green arm that holds the gripper is not connected to any servo, just to the base.

Thanks!
 
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  • #2
You will need to ascertain which geometry of the system will produce the maximum load on the operation of a given servo. From there it should be a simple exercise to solve for the moments and torques (as required for a desired acceleration). The other way to proceed involves exact solution of the system, probably using Lagrange multipliers (?) I presume there is software on the shelf that will do this.
 
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  • #3
Welcome to PF.

You will need to reduce the design to straight line link lengths, between pin positions, and then the angles between the pins. Think of the links as a chain of 2D vectors, stretching from the base to the load, via the pin position points.

You then apply the maximum load to the virtual structure, and follow how that force flows back through the link structure, to become a torque at the servo. Since it is a 2D linkage, I would solve it numerically.

By sweeping the servo angle/length in small steps, through all possible combinations of geometry, you search the range for the maximum servo torque. Look closely near the maximums, to make sure that the torque is bounded, not infinite.

Check that the axial tension or compression in each link is within design bounds, and that the pins and bearing surfaces are sufficient for the loads involved.
 
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  • #4
can you provide the calculations by assuming the the links lengths and weights?
 

Related to Torque required to move robot arm (special linkage)

What is torque and why is it important for moving a robot arm?

Torque is the measure of the rotational force that causes an object to rotate around an axis. It is crucial for moving a robot arm because it determines the arm's ability to lift and maneuver loads. Adequate torque ensures that the robot arm can perform its tasks efficiently and accurately without stalling or failing.

How do you calculate the torque required for a specific joint in a robot arm?

To calculate the torque required for a specific joint in a robot arm, you need to consider the force exerted by the load, the distance from the joint to the load (lever arm), and any additional forces due to acceleration or friction. The basic formula is T = F * d, where T is torque, F is the force, and d is the distance from the pivot point to the point where the force is applied. For dynamic calculations, you also need to account for the inertia and angular acceleration of the arm.

What factors influence the torque requirements for a robot arm's special linkage?

Several factors influence the torque requirements for a robot arm's special linkage, including the weight and distribution of the load, the length of the arm segments, the speed and acceleration of the arm movements, the friction in the joints, and the gravitational forces acting on the arm. Additionally, the type of linkage and its mechanical advantage can significantly impact the required torque.

How can you optimize the design of a robot arm to minimize torque requirements?

To optimize the design of a robot arm and minimize torque requirements, you can use lightweight materials to reduce the arm's overall mass, design shorter arm segments to decrease the lever arm distance, incorporate counterweights or springs to balance the load, and use high-efficiency bearings to reduce friction. Additionally, employing advanced control algorithms can help manage and distribute the torque more effectively across the joints.

What tools or software can assist in calculating and simulating the torque for robot arms?

Several tools and software can assist in calculating and simulating the torque for robot arms, including CAD (Computer-Aided Design) software like SolidWorks and AutoCAD, which allow for detailed modeling and analysis. Robotics simulation software such as MATLAB and Simulink, ROS (Robot Operating System), and Gazebo can help simulate the dynamic behavior and control of the robot arm. These tools enable engineers to visualize, test, and optimize the torque requirements before physical implementation.

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