Augmenting the sensitivity of the gripper

afritz 2017-01-19

Hello everyone,
i'm Ariane from Germany and i'm very new to robotics(2weeks). I m working with UR10 in combination with 2 finger Gripper und FT 150 Sensor.
At our company we want to grab Carrier from an tower and bring it to a spindle for a show case. So we extended the gripper arm with two metal plates (screwed on the gripper up and down).
Now the gripper does not detect any object, that are only fetched by the plates... or he might squeezed the carrier before he marked it as detected
Is there any possibily to augment the sensivity of the gripper or the FT 150? Or should i write any program code to talk directly with the sensor or it is not possible...
Thanks a lot for your help
Best regards

Etienne_Samson 2017-01-19

@afritz your gripper should be able to detect anything over 1.2mm thickness, even if you did custom fingertips, could you show us your setup with some photos ? Maybe send a sample of your program ?

afritz 2017-01-23

@Etienne_Samson here is a picture
At this picture we are moving the gripper step by step to its close position.
Even that there is already a contact between our gripper and the carrier, no object is detected.
We did improve the fingertips by making two plates(above). Now at least when we close the grippe to 100% now he shows that he has detected something. It would have been better that he detects it early otherwise the carrier is squeezed more than necessary.
We have no programm code: we were just checking when the gripper will set object_detected to true and its seems to appear a little bit later than expected.
A question in general: is there another way to have control on the sensitivity for example by communication with the FT150 sensor directory or something like that?

Etienne_Samson 2017-01-24

@afritz those fingertips exceed our maximum dimensions specified in the manual. The object detection will be less reliable due to the deformation of those fingertips, in order to have a reliable detection they would need to be perfectly rigid. Gripper force will be affected too, and Gripper maintenance requirement will be increased.

You could indeed use the FT sensor to detect the weight of the object, it would be fairly easy. You read the Mx or My signal and use the length of that setup as a lever to estimate what mass is present or not. This is commonly used for quality inspection applications, it works.

matthewd92 2017-01-24

The thing that we have seen on long fingertips is to put about 1.5 to 2.5 degrees so that the tips touch first it helps to take up the backlash in the gripper and improves both the detection ability as well as the holding forces, especially at the end of the fingers.

afritz 2017-01-26

Ok have many thanks for your answers. I will transfer it to those who have built the gripper. For now i m not in the office so i don't what they are doing.