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SC Series Controllers
Appendix A
15
Appendix A
Supplementary documentation to better understand the STANLEY SC Controller, QPM EB, EA, EC, E Series
corded tools, and QPM B-Series cordless tools.
15.1
Torsion factor
For all STANLEY electric assembly tools, the angle information is measured by the angle encoder at the motor..
All things can deflect when loaded. Just as a long steel bar attached to a socket to produce high torque will
deflect, likewise the gears within an assembly tool will deflect when subjected to the torque loads. In effect, the
gears act as a torsion spring between the rotor and the socket, and it is the deflection of this spring that can give
false angle data. In addition to the angular deflection within the gears of the tool, there can also be deflection of
the parts of the joint.
Whenever this deflection is present in the tool or the joint or the tool mounting device, the angle information
derived from the encoder will indicate a larger angle than the tool output actually rotates. This error is directly
proportional to the torque level. That is, the deflection at 40 NM will be twice that at 20 NM.
In a torque vs. angle curve of a fastening cycle, at the end when the torque reaches its maximum value, the
angle will also be at its maximum value. After shut off, as the torque falls to zero, the angle should remain at its
maximum value. But in the typical torque vs. angle curve, as the torque falls to zero, the angle also appears to
fall some amount. This is not because the fastener is being loosened. It is actually the resolver indicating that
the angular deflection of the gears is relaxing to the neutral position. In this case, the maximum angle indicated
at the maximum torque was incorrect. The resolver indicated more angle than the tool output actually rotated.
To correct for this slight error in angle data, the SC controller has a STANLEY-exclusive solution. The Torsion
Factor allows the user to input a value that compensates for the torsional spring rate of any part of the fastening
system (the gears of the tool, the joint components, or the tool mounting device), and this factor is used to
correct the angle reading throughout the fastening cycle. This factor is entered as Degrees per NM, and its
default value is zero. If the default value is used, there will be no angular correction. If a value of 0.1 is used,
each angle data point (every millisecond) will be modified by subtracting 0.1 times the torque value. For
example, at 15 NM, the controller will subtract 1.5 degrees from the angle reading for that sample. At 30 NM,
the controller will subtract three degrees for that sample.
The easiest way to determine the correct value for the Torsion Factor is to look at a torque vs. angle trace with
Torsion Factor set to zero. The amount of degrees that the socket appears to loosen after the maximum torque,
divided by that maximum torque is the Torsion Factor. For example, consider a torque vs. angle trace that
indicates a maximum torque of 40 NM, and the maximum angle at this torque of 50 degrees. But the angle
appears to loosen by four degrees as the torque drops to zero. The Torsion Factor can be determined by
dividing four degrees by 40 NM to arrive at a Torsion Factor of 0.1 degrees per NM. When this value is entered
into the Torsion Factor parameter, each angle reading will be corrected by this factor. When this factor is set
correctly, any torque vs. angle trace will now indicate no apparent loosening of the fastener as the torque drops
to zero after shut off; which is exactly as it should be.
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