Robotics

Hi Giannis Letsos,

First of all, can you please tell which simulation software/package are you using - the one that you mentioned in the second line of your question?

And to answer your question "In which situation is the joint move preferred to the linear move?" - direct answer is: It really depends on the path that the TCP needs to take during its motion from one point to another.

To explain it shortly with an example:

Suppose the TCP has to go from point A to point B. Now let's say, you want to save time in the maneuvering and you want it to take the shortest path i.e. a straight line path (assuming that there are no singularity points on that line) between the two points. In this case, a Linear Move is preferred as it'll disregard the constraints on the angular displacements of each joints (& their actuators) and will only focus on achieving the straight line path of TCP.

Now in a parallel scenario, say you want to maneuver between these points utilizing the least power (assuming the straight line path in this case isn't the easiest to pull off for the joint actuators at low power), you will choose a Joint Move. In this move, the focus will be the angular rotations of the rotary actuators at each joints with their constraints, in the center of path planning between A to B.

I hope my answer helps you.

Please feel free to ask any further questions, I'll try to answer.

Thanks,

Harshil.

Robodk is the simulation that I use. I am working on a Human-robot collaborative environment. As I see in ISO 15066, the constraint for max velocity of the TCP, is enough in order to ensure safety, at least for free transient contacts (figure A.4). In ROBODK, there is the option to set linear constraints for a joint motion.

Traditionally, a joint move is constrained by setting angular velocity and acceleration. In this way, it is most likely for the joint move to be faster than the linear one, and as I see, this is one of the reasons for someone to prefer joint to linear.

I think this is what you mentioned above '...you will choose a Joint Move. In this move, the focus will be the angular rotations of the rotary actuators at each joints with their constraints, in the center of path planning between A to B'.

So, is it ok to program a joint move with linear constraints (and not the angular constraints)?

Thank you for your help!

"Traditionally, a joint move is constrained by setting angular velocity and acceleration. In this way, it is most likely for the joint move to be faster than the linear one, and as I see, this is one of the reasons for someone to prefer joint to linear." - Precisely! Basically in most general cases (of RRR) types of robotic arms, Linear moves are for traversal for doing work (e.g. pick and place) and Joint moves are for simple traversal (using the most "comfortable" actuation for all the actuators).

"So, is it ok to program a joint move with linear constraints (and not the angular constraints)?" - I believe that in ideal cases you can. Because then based on those linear constraints (that you define while programming), the processing/computing unit should be able to recalculate the Inverse and Forward kinematics models and it should be good to go again with the new parameters! Although sometimes the robot's environment may restrict some of your given constraints. So my suggestion would be - while trying this "new stuff", please make sure to reduce the speed of the joints and keep close to the Emergency stop (in real life, not in the simulation!).

Be safe!

Best,

Harshil.