Keywords

1 Introduction

Pedal button is a kind of device that moves up and down to finish mechanical transmission. It is widely used in mechanical and medical equipment when it is more convenient for foot operation or the machines do not need to be controlled accurately. Travel length refers to the maximal move distance of pedal button during the up-and-down motion. Diameter is the size of button which contacts with the sole of foot. Diameter and travel length are the most important factors [2] which affect operation comfort. Few research has been done on pedal button. Some text books gave suggest value on diameter and travel length without original data.

2 Methods

Diameter and travel length were the two variables which affected people’s feeling simultaneously, so the experiments adopted control variate method. The two factors were respectively studied in two parts of experiments research their influences on subjective assessment. The assessment method adopted subjective method–rating on a scale [1]. Numerical scales with end points defined by word descriptors. The nine points from −4 to 4 were symmetric distributed by the midpoint “0” which represented “suitable”, the negative and the positive represented respectively different level of small and big. Absent descriptors were the median level (Table 1).

Table 1. Assessment on dimension and travel length
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3 Experiments

Experiments were conducted with 81 subjects (52 males and 29 females). These subjects aged from 18 to 62 and were healthy. Measurements of height, weight, foot length and breadth (right foot) of the subjects had been done before the experiment, stature and dimensions of subjects are shown in Table 2. The subjects included the old and the young, male and female, the 5th percentile female and the 90th percentile male. All the subjects were asked to wear the same kind of shoes which were moderate in hardness to eliminate shoes’ effects on subjects’ feel of the pedal button.

Table 2. Stature and dimensions of subjects
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An equipment (shown in Fig. 1) was specially designed for the experiments. There is a platform on the top of this equipment, pedal buttons with different diameter could be installed on the platform. Seventeen pedal buttons were designed, diameter ranged from 10 to 90 mm and the interval was 5 mm, as shown in Fig. 1. Pedal button travel length could be adjusted in this equipment, it ranged from 0 to 40 mm.

Fig. 1.
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Pedal buttons and equipment for the experiments

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Part 1 of the experiments was about diameter evaluation of pedal button. At first, travel length was set to 10 mm. Subject stood on the platform of the equipment and was asked to depress the pedal button down with the right foot and heel kept on the platform, gave the score of pedal button diameter. Seventeen pedal buttons were assessed in random order. Then travel length was changed to 20 mm, 30 mm and 40 mm respectively to evaluate diameters of the 17 pedal buttons. The subjects could depress each pedal for several times if they want to. They were not allowed to see the pedal button during the experiments. Experiment states of this part were shown as the left part of Table 3. AS- assessment. Units of travel length and diameter are millimeter.

Table 3. Experiment states of two parts
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Part 2 of the experiments is about travel length evaluation of pedal button. Experiment states of this part were shown as the right part of Table 3. At first, pedal button of 30 mm diameter was installed to the top platform of the equipment. Subject stood on the platform of the equipment, and was asked to depress the pedal button down with the right foot and heel kept on the platform, gave the score of pedal button travel length, travel length of 8 mm, 16 mm, 24 mm, 32 mm, 40 mm were evaluated randomly during this experiment. Then pedal button of 50 mm, 80 mm diameter were installed to the platform respectively, five travel lengths tested above were evaluated as the same way of 30 mm diameter pedal button.

4 Results and Discussion

Data were analyzed in SPSS (Statistical Product and Service Solutions) and Excel. The scores on each diameter or travel length were averaged as shown in Figs. 2 and 3 Standard deviation was shown on each bar chart.

Fig. 2.
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Results of diameter evaluation in different travel lengths

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Fig. 3.
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Results of travel length evaluation in different diameters

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Data in Fig. 2 shows that evaluation on diameter in four travel lengths of 10 mm, 20 mm, 30 mm, and 40 mm have the similar distribution. Scores changes from negative through ‘0’ to positive when the pedal button diameter changes from 10 mm to 90 mm. When the travel length is 10 mm, absolute value of scores on diameters of 55 mm to 75 mm are less than ‘1’ and close to ‘0’ which means ‘suitable’. Similarly, suitable diameters are 55 mm to 80 mm on travel length of 20 mm, 50 mm to 85 mm on travel length of 30 m. 50 mm to 70 mm on travel length of 40 mm. Based on the results, we suggest suitable pedal button diameter of 55 mm to 70 mm.

Data in Fig. 3 shows that the evaluation on travel length in diameters of 30 mm, 50 mm, and 80 mm have the similar distribution. The scores are close to ‘−2’ which means ‘small’ when the travel length is 8 mm. Scores get close to ‘0’ which means ‘suitable’ when the travel length is between 16 mm and 24 mm. Scores are bigger than ‘2’ which means ‘big’. So we suggest pedal button travel length of 16 mm to 24 mm.

The averages scores on diameter or travel length are well in distribution. The standard deviations of each average are less than 1.6, the maximum is 1.5026 and the minimum is 0.5919 which are small relatively compared to the bound of assessment. The SD means that the scores fluctuates in a range that we can accept.

The two factors-diameter and travel length ANOVA using SPSS indicates there is no significant difference (p < 0.05). As we can see scores of diameter in different travel length has the similar distribution, and vice versa. Thus we can infer that diameter and travel length are independent within limits.

Diameter of 55 mm to 70 mm and travel length of 16 mm to 24 mm are suggested as the most comfort extent. This results are more accurate than the recommend value of Lai [1] and are suitable for Asian. He recommend diameter of 50 mm to 80 mm and travel length of 12 mm to 60 mm. The results can be used to design pedal button to improve operating comfort.