WPC 1000 User Manual 1125100
Initialization, Setup, and Checkout 3-23
Tbm is the additional time added to the Stopping Time of the press to allow for brake wear
and is used to calculate the brake monitor’s Stop-time Limit (see Calculating the Stop-time
Limit, page 3-16). The Tbm value is usually calculated by multiplying the press’s Stopping
Time at Top-stop by a predetermined factor based on the age of the brakes. The factor for
new brakes is 0.20 (i.e., 20%), that for old brakes 0.10 (i.e., 10%).
The depth penetration factor (Dpf) is a measure of how far an object, like an operator’s hand,
can move through the light curtain before the light curtain reacts. Dpf is related to the light
curtain’s object sensitivity, which is the smallest diameter object Shadow can detect anywhere
in its field.
Object sensitivity (S) for Shadow 8 is 1.18 in. (30 mm) with beam centers of 0.79 in. (20 mm).
(See Table 3-4 for the object sensitivity of other Shadow models.) Based on S and ANSI
B11.1-2009, Dpf = 3.07 in. (78 mm).
Example: Calculating the Safety Distance for a Light Curtain Using the ANSI Formula
The ANSI formula is
Ds = K x (Ts + Tc + Tr + Tbm) + Dpf
The following value is a constant:
K = 63 inches per second
We will use the following values for the variables in the formula:
Ts + Tc = 0.190 sec. (result of the 90° stop-time test)
Tr = 0.059 sec. (response time of Shadow 8 with 202 in. combined length including extensions)
Tbm = 0.035 sec. (see Example 2 in Stop-time Limit Calculation Examples, page 3-16)
Dpf = 3.07
Putting these values into the formula, we get:
Ds = 63 x (0.190 + 0.059 + 0.035) + 3.07
Ds = (63 x 0.284) + 3.07
Ds = 17.89 + 3.07
Ds = 20.96 in.
The light curtain must be mounted 20.96 in. away from the pinch point.
ANSI SAFETY DISTANCE FORMULA FOR USE WITH TWO-HAND CONTROL
The formula for safety distance when using a Two-hand Control as a safeguarding device is similar
to the formula above, but does not include the response time of the light curtain nor the depth
penetration factor. The following is the ANSI formula for calculating the safety distance for use
with Two-hand controls:
Ds = K x (Ts + Tc + Tbm)
If you use a Two-hand Control as a safeguarding device, use this formula and perform the
calculation in a fashion similar to that described for the light curtain formula.
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