Safe Stopping Distance; How To Calculate A Stopping Distance - Mitsubishi Electric MELFA CR800 Series Instruction Manual

7. SAFE STOPPING DISTANCE

The concept of the maximum stopping distance of the robot is described below.

7.1 How to Calculate a Stopping Distance

Assuming that the power supply to the robot controller is shut off during operation or that an error triggers the SS1
function, the maximum stopping distance in the worst scenario can be approximated by the following formula.
(Assume that the robot has brakes on all the axes.)
d : Maximum stopping distance
max
V : Maximum speed (Equivalent to the SLS monitoring speed when the SLS function is enabled)
max
T : Reaction time (time from error detection to stop) (Approximately 7.1 msec)
res
T : Maximum stopping time (Differs from robot to robot, see chapter 7.2 )
max
α : Safety factor (1 or more)
Caution
position monitoring plane
Safety sphere
Deceleration start
<Maximum speed>
When the safely-limited speed function (SLS) is enabled, detection of a speed exceeding the SLS monitoring
speed causes the SS1 function to immediately stops the robot. Therefore, the SLS monitoring speed can be
considered equivalent to the maximum speed. Thus, reducing the SLS monitoring speed enables shortening the
maximum stopping distance when power supply shut-off or an internal error shuts off the driving energy.
When Advanced Mode of the SLS function is configured, each of the X, Y, Z components are monitored for their
speed, which enables restricting the maximum stopping distances for each of the X, Y, Z components. For
example, if there is a safeguarded space in +X direction and the other directions are covered with safety fences,
reducing the SLS speed only in +X direction enables ensuring safety and minimizing impact on tact time.
<Reaction time>
The delay between when an error detection enables the SS1 command and when deceleration starts is
approximately 7.1 ms.
Using the DSI input of the Safety extension unit to stop the robot will have an effect on the DSI filter time
specified in the DSI filter settings. For further information, refer to "(c) DSI filter configuration".
The initial value is 10 ms, therefore there will be a delay of 10 ms until the DSI input is enabled for the input
signal.
If an error occurs in the reading of the DSI input, there may be a delay of up to 72 ms before the signal is read.
= ×
d ( V
max max
The stopping time is affected by how the robot system is configured, the condition of the
robot, and its posture. Therefore, the stopping distance calculated from this formula is
approximate. Use measurements from the system you are using to acquire an accurate
stopping distance.
Depending on the posture of the robot, the arm may droop if the axis does not have a
brake. The amount of droop is not considered in the calculation of the stopping distance
described in this section.
V
max
TCP movement
+ × ×
T ) 0 ( 5 . V T
res max max
position monitoring plane
d
max
Robot stop
How to Calculate a Stopping Distance 7-97
7 SAFE STOPPING DISTANCE
α
×
)
Safety sphere