Keywords

1 Introduction

Many industrial processes require to operate several connectors and plugs such as insert or pull out some plugs, assemble/disassemble some connectors. To accomplish this kind of operation demands appropriate clearance and sufficient force, however, sometimes these conditions can be difficult to meet. Some spatial layouts and designs cannot supply suitable working place for plugs and the others cannot provide users with comfortable room for manoeuvre (Fig. 1). Those two situations make the users difficult or even impossible to complete the work and it can cause great loss in some engineering projects, therefore, study on a kind of connectors and plugs, figuring out the size of their operating-space has great significance. Some studies and trials have tried to measure the operational range of some tools which used by hand, like wrench, bolt, some specific machines, equipment and vehicles, so that the researchers can calculate the working area of that tools. Moreover, many other tests have used the motion capture devices to record the process and trajectory of human motion for finding the scope of human activities.

Fig. 1.
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Two bad conditions for the plugs installation. (a) The gaps is not large enough for both of the plugs. (b) The narrow operating-space make the users difficult to insert the plug.

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The purpose of this study is to combine those two methods, we can calculate the relative minimum operating clearance of those connectors by using the coordinates of the key points on subjects’ hands which recorded by the motion capture system when they are installing and removing the connectors. Following this purpose, we used the motion capture device to find the operating clearance of each connector and installed the different connectors in the same operating panel, search the appropriate layouts. The study finally give the recommendations on the two dimensional layouts of some specific connectors and provide a reference on ergonomic design of the connector operation panel for engineers and designers.

2 Material and Method

2.1 Subjects

Fifteen participants, whose dominant hand is right hand and age ranged from 20 to 45 and the height from 165 cm to 175 cm, voluntarily joined the motion capture trial. The width of their hands ranged from 75 mm to 95 mm and the length of their hands from 170 mm to 190 mm.

2.2 Material

The material and device that the trial required including 13 connectors for total in three different operation types, which we divided into three groups according to the different operation modes. There were three connectors in group A, five in group B and five in group C. We also need a set of test platform and 13 suits of fixtures, which both designed by us. Vicon MX motion capture system and several small markers, which size is 4.0 mm ± 0.5 mm and not less than 20 markers for each hand in each test, as it shown in Fig. 2.

Fig. 2.
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Materials and devices of the trial: (a) three kinds of connectors installing on the platform with their own fixtures, (b) marker attachment for estimating the hand model, (c) the camera of Vicon MX system. (Figure 2-c comes from the introduction of Vicon MX).

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2.3 Trial Design

Considered the individual differences in operating habits, body postures and hand actions were determined when handling various types of connectors. During the connection/disconnection processes we designed and provided that three different operation modes. The first is the back of hand towards the front, four fingers grasp the connector and insert/pull out it, the second is the fingers pinch the connector then screwing it, and the third is the thumb, with index finger or middle finger, pinch the latches at each side of the connector, and insert or unplug the connector (Fig. 3). The connection/disconnection procedures were usually cumbersome, which the operation steps should be simplified by reducing the times of swirling or some others.

Fig. 3.
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Three modes of the connector operation

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Before the test, we have calibrated the equipment and made the participants familiar with the test procedures. Subjects were required to all connectors for three times operation, the command of operating process was instructed by researchers. Then they completed the operation steps stably and consistently. During the entire process of the test if subjects happened to meet operational errors, they would not abort the test, but continued to finish the operation. After the test had been done, researchers were used to observe the recorded image. If the recorded image didn’t meet the test requirement, we had to retest, until the image got to meet the basic requirements of test. As shown in Fig. 4.

Fig. 4.
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Two images of the motion capture trial

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Through the observation and analysis of the operation process, the major joints and wrist position of the hand determined the actual size and relative position of the operating clearance. Therefore, the extreme coordinates in two direction of these joints which named by X max , X min , Y max and Y min was the only need to the test. Through the calculation, we obtain the size of two dimensional operating space in corresponding direction. Set a and b respectively represent the dimensions of the clearance in x and y direction, then there is

$$ \begin{aligned} a = \left| { \, X_{max} {\text{-}}X_{min} } \right| \hfill \\ b = \left| { \, Y_{max} {\text{-}}Y_{min} } \right| \hfill \\ \end{aligned} $$
(1)

After figuring out the sample mean and sample variance of a and b, respectively, we calculate the confidence interval of μ a and μ b through the statistical method, which the confidence coefficient (1-α)100 % is 95 %. Then a confidence interval for μ is given by

$$ \left( {\bar{x} - t_{{{\raise0.7ex\hbox{$\alpha $} \!\mathord{\left/ {\vphantom {\alpha 2}}\right.\kern-0pt} \!\lower0.7ex\hbox{$2$}},\,n - 1}} s/\sqrt n ,\bar{x} + t_{{{\raise0.7ex\hbox{$\alpha $} \!\mathord{\left/ {\vphantom {\alpha 2}}\right.\kern-0pt} \!\lower0.7ex\hbox{$2$}},\,n - 1}} s/\sqrt n } \right) $$
(2)

And the \( \bar{x} \) stand for the sample mean, s stand for the sample standard deviation, n-1 is the degree of freedom. We used the expectation μ a and μ b to construct the installation area for nine connectors among the thirteen, and searched the appropriate layout, measured the size of operating panel. In particular, the five connectors of the nine with a rectangular cross section and the other four with a circular cross section. We tried to lay out the connectors with those two cross section types together and independently, compared each layout with dimension and area.

3 Results and Discussion

The measurement results of thirteen connectors operating clearance is shown in Tables 1, 2 and 3.

Table 1. The results of connector A01 – A03
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Table 2. The results of connector B01 – B05
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Table 3. The results of connector C01 – C05
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The measurement results show that the radius of 95 % confidence interval is quite short and reliable. But the variance or fluctuation of test data is still large, and the operating space itself may be varies to each individual and with instabilities. Causes of instabilities may be in the different of operating strength and skills, or caused by the differences in feel. When different subjects handle the same difficult operation, such instability is particularly prominent. From the overall perspective, the test results basically reflect the feature size of the relative minimum operating clearance of connectors. So we use the expectation of a and b to build the installation area for each connectors and narrowed clearance until it nears to unavailable area. Selected the five connectors with rectangular cross sections construct the two kinds of operating panel (Fig. 5).

Fig. 5.
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Five connectors operating panels (the unit is mm)

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From Fig. 5 we can obtain that the length of both two types are 305 mm and 450 mm, the width of this two panels are 102 mm and 60 mm and the area respectively is 31,110 mm2 and 27,000 mm2. Comparing with the area, the second types is absolutely smaller than the first one, however, the length of the second type is one-third longer than the first type. So it is predictable that the moment of the second panel will be stronger than the first one.

We also selected four connectors with circular cross sections to build the operating panel (Fig. 6).

Fig. 6.
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Four connectors operating panels (the unit is mm)

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The length, width and area of both panels, respectively, are 156 mm and 236 mm, 120 mm and 120 mm, 18,720 mm2 and 18,336 mm2. At last we involved all the nine connectors together and reconstruct a layout for the operating panel (Fig. 7). The length of the layout is 270 mm and the width is 180 mm, the area is 48600 mm2 However, this layout may not be the comfortable one, because it nears to the unavailable zoom.

Fig. 7.
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Nine connectors operating panels (the unit is mm)

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During the test, we found that if the space for operating didn’t hinder the hand, the time and the errors for operation will not change too much for the same subject who is sufficiently skilled. Moreover, the actual interval is generally smaller than the layout which is added up by theoretical clearance from each single connectors. Analysis of operation time and error is not very helpful, and only the layouts category and size is worthy of comparison.

4 Conclusion

The study shows that motion capture system can be used to study the connector’s operability issues, but the results tend to be not strict, it needs to be verified by narrowing the range of availability. At the same time, operations to different kinds of connectors, which is a certain specificity, if such property would be diminished with increasing samples remains to be further studied. Generally speaking, the results of this paper provide some reference for the future study and design of the connector panels.