TCP and Center of gravity

armormodeller

Using a UR5, have the 150 Force Sensor, Wrist camera and the 140 2-Finger Grippers along with a FTS-150-TOOL-104 mechanical plate. Need to know what the center of gravity coordinates are if any one else has done this TCP set-up also.

Do I also need the length and the weight of the additional fingers we are attaching to the 140?

Also, do I need to include the part weight, that will vary.

Gabrielle

@armormodeller The center of mass your system is (1, 0.5, 81.5), all in millimeters. The system of coordinates is the same as the one one the force sensor and the camera. 

Etienne_Samson

@armormodeller we have the center of mass for our product combo listed in each manual in section 6, specification, under mechanical specs. FT-150 is not listed though, we will add it and let you know shortly.

Your second questions I'm not sure to understand, if you are talking about center of mass change with the finger opening don't bother, that's way too little for the UR.

And for the part weight, yes, you should dynamically change the payload in your program, you should be using function set_payload, here is it's description from the UR script manual:

set payload(m, CoG)
Set payload mass and center of gravity Alternatively one could use set payload mass and set payload cog. Sets the mass and center of gravity (abbr. CoG) of the payload. This function must be called, when the payload weight or weight distribution changes - i.e when the robot picks up or puts down a heavy workpiece. The CoG argument is optional - if not provided, the Tool Center Point (TCP) will be used as the Center of Gravity (CoG). If the CoG argument is omitted, later calls to set tcp(pose) will change CoG to the new TCP. The CoG is specified as a vector, [CoGx, CoGy, CoGz], displacement, from the toolmount.
Parameters m: mass in kilograms
CoG: Center of Gravity: [CoGx, CoGy, CoGz] in meters. Optional.

Colin

@Gabrielle
Can you explain your calculation for getting that COG? I am not understanding how you got there from what @Etienne_Samson
posted about the mechanical specs. Thank you.

Gabrielle

Hi @Colin,
I used the 3D cad of the products with the right mass and center of gravity of every product and calculated the resultant center of gravity directly in Solidworks. 
The software calculated that info with the same formula as the one you can use to determine the center of mass of multiple objects. 

Colin

Where are you getting the Robotiq hardware COG components for that calculation? All I can find is the moments of inertia.

David_Gariepy

You can find this information in the specification section of the manual for our product. 
Here you have it for every possible Robotiq product combination. 

Colin

I had thought that those values were for the TCP Position. Thank you. 

Gabrielle

@Colin I used the internal CAD but unfortunately you don't have access to them. You can calculate the same result manually with the information you can find in the manuals of the products.
Here is the information you need : Center of mass of the force sensor, Dimension of the force sensor, Center of mass of the camera, Dimension of the camera, Center of mass of the gripper and Dimension of the gripper.
You can find the formula here and do the calculus