25
Banner Engineering Corp.
•
Minneapolis, U.S.A.
www.bannerengineering.com • Tel: 763.544.3164
P/N 64118 rev. B
Double-Edge Scan
is used to detect two edges of a single object, for example, box
width measurements. Double-Edge Scan requires the selection of a step size: 2, 4, 8,
16 or 32 beams. The sensor uses the steps to “skip” over beams. Double-Edge Scan
works as follows:
1. The sensor activates beam #1 (the beam closest to the sensor cable end).
2. The sensor activates the next beam, determined by the step size. (For example, if
the step size is 2, beam #3 is next; if the step size is 8, beam #9 is next.)
3. As long as the activated beam is unblocked (or “made”), the sensor will continue
the stepping routine until a blocked beam is found.
4. When a blocked beam is found, a binary search is conducted to find the object’s
“bottom edge.”
5. When the bottom edge is found, the sensor begins “stepping” again through the
array until the sensor finds the next unblocked beam.
6. A binary search is again performed to find the second edge.
Note that this scanning method sacrifices object detection size for speed. Similar to
Single-Edge Scan, Double-Edge Scan has some restrictions: the object should provide
a solid obstruction; the size of the object will determine the maximum step size
(Figure 5-14).
Sensor response time is a function of sensor length and scanning method. Typical
scan times are shown in Figure 5-15.
Step Size
Number of Beams
Minimum
Object
Detection
Size
5 mm
(0.2")
10 mm
(0.4")
20 mm
(0.8")
40 mm
(1.6")
80 mm
(3.2")
Maximum Scan Times (in milliseconds)
Array
Length
Straight
Scan
Single-
Edge
Scan
Double-Edge Scan
Step
2 Beams
Step
4 Beams
Step
8 Beams
Step
16 Beams
Step
32 Beams
163 mm
(6.4")
5.8
1.8
3.4
2.7
2.5
2.6
325 mm
(12.8")
10.6
1.9
8.1
5.1
3.6
3.0
2.7
488 mm
(19.2")
15.0
2.1
11.5
6.8
4.5
3.4
3.0
650 mm
(25.6")
20.1
2.1
14.9
8.5
5.3
3.9
3.2
812 mm
(32.0")
24.9
2.1
18.3
10.1
6.1
4.2
3.5
975 mm
(38.4")
30.0
2.1
21.7
11.8
7.0
4.7
3.6
1138 mm
(44.8")
34.5
2.1
25.0
13.5
7.9
5.1
3.8
1300 mm
(51.2")
39.3
2.1
28.4
15.2
8.7
5.5
4.1
1626 mm
(64.0")
48.0
2.3
35.1
18.6
10.4
6.4
4.5
4.8
1788 mm
(70.4")
53.6
2.3
38.5
20.3
11.2
6.8
4.7
Figure 5-14. The effect of step size on
minimum object detection size
Figure 5-15. The effect of sensor length and scanning method on scan time (typical)
Control Module Configuration
Banner Engineering Corp.
•
Minneapolis, U.S.A.
www.bannerengineering.com • Tel: 763.544.3164
NOTE: Scan times are exclusive of serial
communication transmission times.
1463 mm
(57.6")
44.0
2.2
31.8
16.9
9.5
5.9
4.3
1951 mm
(76.8")
58.4
2.3
41.9
21.9
12.1
7.2
4.9
2
4
8
16
32
