Limit Values; Types Of Forces - PreCise PF400 Hardware Reference Manual

PreciseFlex_Robot

Types of forces

There are four types of forces that should be considered and tested when designing a "Collaborative"
robot workcell. These are:
1. Clamping/squeezing force. This is the quasi-static case of the robot pressing a compliant part
of the human body against a surface. This force should be considered when the robot is under
manual control and for low speed collisions.
2. Impact force in free space (Transient contact). This is the dynamic case of the robot colliding
with person where the person is free to recoil from the collision. In some cases the speed and
inertia of the person should be added to the speed and inertia of the robot. The inertia of the
robot will include the payload, the robot structure, and the forward reflected inertia of the motor
and gear train, which can be quite significant. Impact force is considered to be a transient force of
short duration.
3. Impact force against a surface. (Trapping) This is the case where the person or appendage is
trapped between the robot and a hard surface with the robot moving at speed. While this can
be rare for many applications given proper workcell design, it should be considered. High speed
impacts which trap an operator against a surface may be avoided by teaching an "Approach"
position which is a greater distance from a fixture than any operator appendage that might enter
the workcell, and moving to this "Approach" position at high speed, then moving to the final
position at a rigid surface at a slow speed which will not create excessive force in the event of a
trapped operator.
4. Pressure, or force per unit area. 130N of force applied to a large area, for example 50mm X
50mm is quite different from this same force applied to a small area, for example 1mm X 1mm.
Note that ISO/TS 15066 does not differentiate between clamping/squeezing force (low speed) and impact
forces against a rigid surface (high speed) and refers to both cases as "quasi-static" even though they are
quite different, as the high speed impact will include dynamic forces from the moving mass, while the low
speed clamping forces will be mainly due to motor torques.
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Figure 2