Keywords

1 Introduction

Volumes of research results regarding manual operation ergonomics can be found, most of which focuses on the operation of manual push-pull tasks such as the study of the human body strength, analysis of factors affecting the pull-push action forces, and the occupational injury caused by the pushing and pulling force [1–4]. Also, there were some studies concentrating on comprehensive influence analysis on multiple factors which include operation posture, gripping position and load size [5–10]. From a different perspective, this paper emphasized on the study of the comfort ranges of manual operation in standing position.

The role and significance of this study are embodied in the two aspects as follows: (1) evaluating and improving the ergonomics of the manual operating device in the industrial equipment and infrastructures (i.e., the installation location and operation area being convenient for users to operate correctly for the commonly used key button, knob, handle, control rod, etc.). (2) evaluating and improving the layout of the complex control table (i.e., For the power console, traffic scheduling table, cockpit display control panel used by aircraft, train and car, etc., it is necessary that the most important manual control device is installed in the optimal operation area).

Twenty people (ten males and ten females) from ages 18 to 25 years old with good physical health and no movement impairments were recruited as study subjects. The six main processes were as follows: (1) The adjustable height of the operating platform and button mechanism assemblies were designed and developed; (2) The acceptable operating heights of the operator were preliminarily determined by the experiment (approximately 800–1200 mm); (3) With the 100 mm step size as the interval, five test heights and related press operation regions were set, and the natural standing positions of the trial operation were determined; (4) The subjects were asked to complete the operation of the right index finger button press when test personnel recorded the subject’s subjective comprehensive acceptable operating area; (5) Statistical analyses of the test results were performed in order to obtain the acceptable index finger pressing operation regions; and (6) The comfort field chart (table) of standing manual operation was obtained. This research has offered certain practical application values of manual manipulator’s positions in the ergonomics design and evaluation.

2 Experiment on Comfort Ranges of Manual Operation in Standing Position

The comfort ranges of manual operation for a single and light load were studied in this paper. A preliminary investigation during the pre-experiment phase led to a discovery of the manual operation being influenced by gender, age, position and operation of the study subjects. This research mainly concentrated on the test methods and technical routes in which twenty healthy young people were recruited as study subjects. The test data were statistically analyzed, and ultimately, the corresponding comfort chart of manual operation in standing position was obtained.

2.1 Determine Height Ranges of Test Table

A test bench device with adjustable height was designed as shown in Fig. 1. The approximate height range of the operating table was roughly set based on the shoulder height and middle finger to ground distance of the vertical arm of the human body measurement dimension in a standing posture. Then the acceptable height ranges of the test surface were determined from 800 mm to 1200 mm by the increment of 100 mm as the step size according to the lowest and highest height of the press operation.

Fig. 1.
figure 1

Adjustable height operation platform

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2.2 Experiment Process

  1. 1.

    The two row button mechanism was assembled which consisted of ten sets of buttons on each row in the 800 mm height of the platform. These buttons to the same operating force and operation displacement were adjusted, and the same sizes of the button head were chosen.

  2. 2.

    The ranges of the operating region were roughly determined by the arm length of the people in the 95th percentile, which was divided into the horizontal and vertical regions. As shown in Fig. 2, the left graph indicated a horizontal test table, and the right was a longitudinal test Table 

    Fig. 2.
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    Test points layouts

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  3. 3.

    The horizontal test was listed as follows: On the horizontal test table shown on the left side of Fig. 2, the subjects completed the pressing operation task on green measurement points in sequence from left to right. The range of the measuring points for the complete task can be achieved, and the press operation comfort zone test in other rows was performed with the same method.

  4. 4.

    The specific process of the longitudinal test was listed as follows: On the vertical test table shown on the right side of Fig. 2, test personnel guided the participants to perceive the comfort of the red point button operation. The comfort ranges of the pressing operation were presented, and the test of other vertical testing points in sequence was completed. The overlap areas of lateral and longitudinal comfort regions mentioned above in steps 3 and 4 were the comfort ranges of manual operation of the study subjects.

  5. 5.

    The comfortable ranges on the other heights were conducted according to the aforementioned steps.

3 Experimental Results

Twenty young people, ten men and women, with good physical health and no movement disorder were tested, respectively. Test scenarios are shown in Fig. 3.

Fig. 3.
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The index finger pressing operation comfort zone test scenarios (left chart shows the longitudinal test, the right is lateral test)

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The results of all the tests showed that 800 mm and 1200 mm were more dispersed. The 800 mm table was lower so that the comfort of the operation was poor while the 1200 mm operating table was higher than that of the general standing elbow height value. Because the study data of these two tables were relatively discrete, it was difficult to find a comfortable boundary. Only the data of the large number of subjects can be clearly defined in the scope of the comfortable boundary, which was only given in the test results of the 900 mm, 1000 mm, and 1100 mm operating height of the male and female on the right hand index finger pressing operation comfort regions. As shown in Figs. 4 and 5, the shape and trend of the male and female graphics were consistent via the trapezoid. The comfort region was located on the front right side of the operator, and the longer operating range was close to the operator. The operating range was shorter when further from the operator. At the left edge of the operating region, the trend was gradually increasing while a gradual decrease was present at the right side of the operating region. The performance of the left and right sides of the boundary line were not smooth due to the small sample size.

Fig. 4.
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Ten young male standing manual operation comfortable zone distribution

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Fig. 5.
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Ten young female standing manual operation comfortable zone distribution

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4 Conclusions

  1. 1.

    In this paper, the experimental study was undertaken to assess the comfortable location in standing position and light load manual operation. A manual operation test bench with adjustable height was designed and developed. Twenty young men and women were in the operating positions of the right index finger button pressing, testing the operation comfort in standing state under different bench heights. A comfortable region distribution map of three operation positions was obtained. This research demonstrated that certain practical application values of the manual manipulator’s position contributed to ergonomics design and assessment.

  2. 2.

    The small sample size of twenty tests might directly affect the accuracy of the test results. As a result, the operation region of the left and right boundary was not smooth. A larger sample would lead to a solid scientific method to obtain a comfortable location region distribution of manual operation in the standing state.

  3. 3.

    Various factors affect the comfort of manual operation, which were only limited to the influence of the test manual operation position on the comfort of operation. Furthermore, the operating force and the operating frequency of the manual operating comfort could have a greater impact via weight analysis of the impact of the main factors on the follow-up plan. Establishing a location comfort assessment model for manual operation would contribute to critical practical values of manual operation in ergonomics design and assessment.