Command the gripper with 0–1 ratios for position, speed and force

[bcastets-robotiq]

Issue

The ROS node currently takes SI value for position (radian), speed (m/s) and force (Newton).

This cause the following paint points:

• Difficult for to understand what is the maximum possible value without checking documentation.
• Speed vary depending on the gripper model.
• As there is no direct correlation between the force parameter and the actual gripping force in Newton, it is incorrect to use Newton unit.

Proposed solution

Use 0-1 float ration for position, speed and force by default. This makes it clear what it the maximum and the minimum and works for any gripper model.

This could also be 0-255 unsigned interger by default for position, speed and force.

There is a choice to do here:

• Control the gripper with 0-255 unsigned integer is the best to be able to precisely set the gripper registers. This gives the possibility to control the grippper from its core.
• Control the gripper with a 0- foat value may easy the ROS programming because it is most probably easier to control the position on the grippre with a continuous value. This is to be confirmed, I don't know what are the current control pratice.

Things to keep as an option

Node could be adjusted to offer control of the opening and of the speed with SI unit (m, m/s). It is usefull to have this capability but it requires some manual settings (precise open and close position, precise grippre model,...)

[ebarnett3]

Note that any features that make sense for all users of the SDK and not just for ROS should go in the SDK. So I would suggest to put the conversion calculation there, with only the ros surface for accessing the SDK functions here.