［ Systems・Components ］

Development of a Visual Rope
Tester
Keywords

Yoshiki Nota,
Yutaka Shoji,
Mitsuru Kato

Image analysis, Elevator rope, Appearance check

Abstract

The number of skyscrapers being built worldwide is increasing and highspeed elevators with long working distance are becoming more and more popular. As a result, maintenance and inspection sites are required to shorten andimprove their inspection work. In particular, the inspection of wire ropes is themost common method of inspection uses calipers or visual inspection. As theoperating distance becomes longer, the working time also increases in proportion to the lengthened distance. It is important to note, that depending on theworkersʼ level of proﬁciency, there is the challenge of human error in visual andcaliper value measurement.
We, therefore, developed a “Visual Rope Tester” to automate the wire rope
inspection using image processing technology. In this system, two cameras takepictures of the wire rope and the system analyzes the images. This improves theefﬁciency of the inspection process and reduces human error of wire rope
measurement.

1 Preface

2 Inspection Items for Wire Ropes

With the growing use of high-speed elevators,
the time and accuracy level of elevator inspection
are challenging. The market calls for the improvement of these issues. Among the multiple inspection items, the inspection of wire ropes is done bycalipers or visual inspection of a service worker.
Since there are many manual processes likecaliper-based measurement and visual inspection,measurement errors can easily occur by service
workers. The number of inspection points increase
with the increase of distance in elevator operation.
Inspection work, therefore, tends to take a longtime.
We, together with Nippon Otis Elevator
Company, developed a “Visual Rope Tester” to support the inspection process. In this system, twocameras take the picture of wire ropes of an elevator in operation and the system analyzes theimages. The analysis allows for quick inspections
with no measurement error. In addition, the noncontact inspection improves the safety of the inspection work. In this paper, we introduce a newly developed Visual Rope Tester.

Fig. 1 shows wire rope inspection items. Theseare the value of the wire rope diameter, the lengthof the wear mark, and the stranded wire breakage. The inspection method for each item is as follows.

2.1 Rope Diameter
While the elevator is operated, each rope wireis gradually shaved and loses its diameter. Thisdiameter is measured with vernier calipers. Since
the wire rope is a stranded wire, its surface isuneven. At the time of inspection, a service worker(a) Diameter

Fig. 1(b) Length ofabrasion mark(c) Strandbreakdown

Wire Rope Inspection Items

Inspection items cover rope diameter, abrasion mark, and strandbreakdown.

MEIDEN REVIEW Series No.181 2021 No.135visually checks the point indicated by an arrow
mark as shown in Fig. 1 (a) where the diameter
appears the widest. This size is measured with vernier calipers.

2.2 Length of Abrasion MarkThe length of abrasion mark caused as a resultof shaving of stranded wire surface is measured
with vernier calipers or a ruler as shown in Fig. 1 (b).
The measured length value is recorded.

2.3 Strand Breakdown
The strands that make up a wire rope are subject to progressive wear. The breakage of the barewire will take place as shown by the circle in Fig. 1(c). At the time of inspection, the broken strands arechecked by visual inspection and touch examination (palpation). After, the service worker records
the number of breaks.
In wire rope inspection, since there are many
inspection checking items involving visual identiﬁcation and measurement by vernier calipers, inspection work time becomes longer. This becomes afactor in causing measurement errors.

3 System Conﬁguration
Fig. 2 shows an overall conﬁguration. Thissystem is composed of a camera and units of control and analysis. Details of each unit are as follows:

Elevator rope

Photo-taking
scope ofCamera 1

Front lightLine sensor
Camera 1

Rear light

Photo-taking
scope ofCamera 2

Line sensor
Camera 2

Synchronizing
signalImage signal
Elevator
controller

Fig. 2

Speed data

Control andanalyzing unit

Overall Configuration

The overall conﬁguration of the visual rope tester is shown.

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3.1 Cameras for Wire Ropes
The wire rope photo-taking equipment is composed of two ( 2 ) line sensor cameras and two lighting units. Each line sensor camera can take images
at a high frequency and high resolution. When sucha line sensor camera is used, it is possible to checka wire rope at the intervals of several millimeters
while an elevator car goes up and down at a speedof 600 m/min. While the elevator is in operation,
wire ropes cause sway and vibration. This systemis, therefore, equipped with two cameras to establish a stereoscopic conﬁguration in order to measure the width of sway caused by wire ropes in operation. Based on this measurement, impacts bysway and vibration caused while the elevator goesup and down can be corrected later in measurement
and the wire rope diameter can be measured precisely.
A lighting unit used for this system is installedat two positions, front and rear, with the wire rope inbetween. By illuminating the wire rope from the front
light, the abrasion mark length and strand breakdown can be photographed. When the wire rope islit from behind with the rear light, a silhouette of thewire rope can be made clearer so that diametermeasuring accuracy by image analysis can beimproved.

3.2 Control and Analytical Unit
This equipment takes photo-taking system
control and image analysis. For the control of thephoto-taking system, the elevator speed data isacquired from the external elevator controller inorder to control the cameraʼs frame rate. By regulating the frame rate of the camera properly inresponse to the speed data, images of a wire rope
can always be taken at constant intervals irrespective of the elevator speed. The analytical function
part performs the image analysis.
The proposed inspection system is composedof the aforementioned two units. In many cases,
applicable high-rise buildings of this system are
equipped with multiple elevators in the building. For
this reason, this system is made a portable typeso that a single inspection system can cover multiple elevators. Table 1 shows a comparison witha conventional inspection method. By using thissystem, we can realize the reduction of inspection
labor hours and improvement of measurement
accuracy.

Conventional

Newly developed system

Positional movement 24 m/min Measurement at 24〜600 m/min→ Measurement of a specificposition
Measurement for each rope

Batch measurement of all ropes

Presence of individual differences in measuring positionsand accuracy

No individual differences inmeasuring positions andaccuracy

Visual checks on anomaly
positions

Saved in images and postcheck is possible.

Rope 1
diameter(mm)

Comparison of the developed system with conventional inspection method is shown.

Rope 2
diameter(mm)

Comparison with Conventional Inspection
MethodRope 3
diameter(mm)

Table 1

Fig. 422.4
2221.621.2
114.40114.36114.32114.28114.24114.20114.36114.32114.28114.24114.20114.28114.24114.32
Measuring position (m)114.20

22.4
22
21.6
21.2
114.40
22.4
22
21.6
21.2
114.40114.36

Analytical Results

The analytical results of rope diameters are shown.

Fig. 5Fig. 3

Image Taken by the Tester

An image of elevator ropes is shown. It was taken by the tester ata speed of 600 m/min.

4 Veriﬁcation Test
In order to verify the effectiveness of the newly
developed system to an actual elevator in operation,
the following tests were conducted.

4.1 Wire Rope Diameter Measuring Test
In the wire rope measurement test, the system
was used to photograph a wire rope of elevator
operating at 600 m/min and measured the diametervalue. Fig. 3 shows an image taken by the tester.
Even in an elevator operating at a high speed, thewire rope can be photographed accurately. Fig. 4shows the analytical results. Each graph shows thediameter of each wire rope and the uneven shape ofthe three stranded wires are measured. We compared the systemʼs measured value with the service
workerʼs vernier caliper value and veriﬁed that themeasurement was made within 0.2 mm of error
range.

Images of Abrasion Mark Analysis

Images of abrasion mark analysis are shown. The left image istaken before analysis and the right image shows the analyticalresult.

4.2 Wire Rope Abrasion Mark Length Test
For the abrasion mark length test, we photographed and analyzed an abraded rope with oursystem and veriﬁed the adequacy by comparing itwith conventional vernier calipers values under thecircumstances of assuming an elevator moving at
150 m/min. Fig. 5 shows images of abrasion markanalysis. White dots in the left image show a traceof abrasion on the rope surface. This image wastaken by illuminating the rope surface by the frontlight. The right image shows the result of abrasion
mark measurement by actual image-based analysis. The straight line displayed on the abrasion markindicates the measured length of the abrasion mark.
According to this result, it is possible to conclude
that each abrasion mark length of a rope can bedetected accurately. We also tried to compare oursystemʼs measuring results with vernier calipers values and conﬁrmed that the measurement error iswithin 1.0 mm.
MEIDEN REVIEW Series No.181 2021 No.137

Position of simulated breakdown

Fig. 6

Position of simulated breakdown

Images of Simulated Strand Breakdowns

Images of simulated strand breakdown are shown. The left
image was taken with a digital camera and the right image shows
the result of a photo-taken with a line sensor. A strand breakdown can be photo-taken by using a line sensor camera.

4.3 Wire Rope Strand Breakdown Test
For the wire rope strand breakdown test, 0.4 mm
tapes were placed in two positions simulating astrand breakdown assuming under the circumstance of an elevator operating at 150 m/min. For
this veriﬁcation, the developed system photographed the simulated breakdowns and analyzed
them. Fig. 6 shows images of the simulated strand
breakdowns. The left image shows 0.4 mm tapes
simulating the breakdown placed in two positions
on an actual rope. The right image shows a simulated breakdown photographed by the developed
system. Using this system, a 0.4 mm strand breakdown could be photographed. Fig. 7 shows theresult of the simulated strand breakdown analysis. A
circle mark shows a spot where the detected strand
breakdown is located. A short straight line (centerline in ) is a plot in the image domain where thebreakdown occurs. In this way, a strand breakdown
can be detected from an image of a rope in operation.

Fig. 7

Result of Simulated Strand Breakdown Analysis

The result of analysis on an image of simulated strand breakdown is shown. Circle marks indicate the positions where strand
breakdown is detected.

5 Postscript
To attain higher efﬁciency and improved accuracy of wire rope inspection work, we developed arope inspection system called the “Visual Rope
Tester” using the image analysis technology. With
this system, wire rope diameter, abrasion marklength, and strand breakdown can be measured. As
a result of veriﬁcation tests of the developed systemusing an actual elevator in operation, we veriﬁedthat the system can measure ( 1) the rope diameterat an elevator speed of 600 m/min and with an accuracy range of 0.2 mm or less, ( 2 ) abrasion marklength at a speed of 150 m/min and with an accuracy range of 1.0 mm or less, and ( 3 ) strand breakdown of 0.4 mm.
In the future, we intend to apply this system not
only for elevators but also for other wire-rope-based
products such as cranes and construction machinery.
・All product and company names mentioned in this paper are
the trademarks and/or service marks of their respective owners.

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