1 Introduction

With the development of technology, products become more and more electronic. There are many different user interfaces in the process of interaction between people and products are made up of various operating units. Before user start to operate the product, they would make an impression about the method of operation and operation flow in their mind in advance by observing the user interface on product. If this impression is consistent with the design of user interface, we can feel that the product is easy to operate. Like above, so that we can say the feeling of the operating units is an important element that could decide the product operability. Here, the appearance of operating units is composed of various factors that are related to the shape, so that we can think every change of those factors would have a great impact on the feeling of operation [1].

Figures 1, 2, 3, 4 and 5 are the results of the classification about the shape of the button that appears to be circular in the face (The following is called a circular button) of daily life.

Fig. 1.
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The model’s side that has an inclined plane with upward and inward, the gap between the button and the plane can be seen, and the top surface changes from raised to concave

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Fig. 2.
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The model’s side that has a vertical plane, the gap between the button and the plane can be seen, and the top surface is flat, height ranges from lower than the plane to higher than the plane

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Fig. 3.
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The model’s side that has a vertical plane, the gap between the button and the plane can not be seen, and the top surface changes from the horizontal to convex, the button is higher than the plane

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Fig. 4.
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The model’s side that has an inclined plane with downward and inward, the gap between the button and the plane can be seen, and the top surface changes from the convex to the concave, the height changes gradually from higher than the plane to below the plane

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Fig. 5.
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The model’s side that has a vertical plane, the gap between the button and the plane can be seen, and the top surface changes from the convex to the concave, and the underside is higher than the plane

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By the above analysis of the shape of the circular button, it is found that the shape of the circular button is determined by the shape of the side and the top surface, Relative to the height of the plane where button is and the division between the plane and the button. The combination of different shapes of elements will bring a lot of changes in the feeling of operation.

In this study, we will take the button of car’s heater control as the main research object.

With the advancing of science and technology and the development of the automatic driving, All operations related to driving a car are going to the direction of the technology control With this change, high-tech equipment that equipped in car are increase gradually.

According to the result of investigation from JD Power (Fig. 6), compared with the result previous year, the installation rate whether voice recognition system or function of Bluetooth connectivity increased in 2015 year [2]. In order to realize the function of the additional high-tech equipment and the change to the direction of technology control, there has been great changes taken place in car’s user interface. The points about “Is it easy to operate?” “Is it easy to understand Operation method” “How about the position” “Is it easy to press button?” and so on which are related to the feeling of operation about user interface became the important factors to improve customer’s satisfaction.

Fig. 6.
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The installation rate about voice recognition system and function of Bluetooth connectivity

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Figure 7 is result of a survey which conducted by JD power in December 2015 for User’s degree of dissatisfaction with vehicle equipment, the lower the score, the less dissatisfaction. According to the result, dissatisfaction can be divided into dissatisfaction of manufacturing and dissatisfaction of design, the score of is still the same as last year 1.7 points, but dissatisfaction of design by last year’s 8.6 points rose to 9.6 points, is 5 times more than dissatisfaction of manufacturing. I think the problems that are related to the feeling of operation such as not easy to use and difficult to understand which caused by design become reasons for user dissatisfaction.

Fig. 7.
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The survey of user’s degree of dissatisfaction with vehicle equipment

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In this study, first, through experiment of operating buttons with different functions to achieve a certain goal based on the impression of operation which formed in the mind in advance before the actual operation in order to achieve a certain goal which can be realized by heater control to make the user’s mental model more clearly.

Through the experiment to evaluate how the change of each factor which related to button’s shape will bring the impact to the feeling of operation to clear the influence between the elements of the shape of the button and the feeling of the operation. And further, make the proposal of a new design of heater control’s user interface that can improve the user experience in combination with people’s unconscious action in daily life as the goal.

2 Consideration on User Mental Model for Heater Control

2.1 Experiment

2.1.1 Experimental Installation and Space Composition

For the experimental installation, HP personal computer and visual line measuring device (Tobii) were used. In addition, we prepared four kinds of Japanese cars’ heater controls (Fig. 8) as user interface to be evaluated.

Fig. 8.
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Four kinds of Japanese cars’ heater controls

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For the composition of the experiment space (Fig. 9), we used the ‘Thrustmaster T500 RS Racing Wheel’ as steering (foil), the SECT international company’s play seat as car seat, and the other operation panel was made 1/1 model with corrugated cardboard.

Fig. 9.
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Experiment space

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2.1.2 Evaluation Method

First, imagined four scenes about when it is hot, cold, need to remove the fog of the glass and use the function of Auto (Fig. 10), and We evaluated the operation on these scenes. There are seven items in Evaluation items (ease of operation, ease of searching, ease of seeing in icons, understandability of icons, similarity with operation images, goodness of feedback, understandability of layout), we conducted seven grades by SD method. We also made a comment on the feeling of operation freely (Fig. 11) [3] Finally, we compared the four types in the questionnaire (Figure 12).

Fig. 10.
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Four scenes assumed

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Fig. 11.
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Evaluation item by SD method

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Fig. 12.
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Questionnaire

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2.1.3 Experimental Method

A total of three men and women at the age of twenty who have driver license but did not have a driving habit had participated in the experiment, the experiment participants sat on a seat on the real space with a gaze measuring device (Fig. 13). According to their own impression on the operation of the four different scenes were operated buttons.

Fig. 13.
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Experimental situation

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After the operation for each type of each scene was completed, evaluation was carried out in a questionnaire. Finally, we compared the four types in the questionnaire and received evaluation.

3 The Influence that the Element of Buttons’ Shape Brings to the Feeling of Operation

3.1 About Shape

We will discuss the concept of shape in this research. Shape refers to the appearance that the eye can see and state [4]. Not only the appearance but also the meaning of the state of things that can be recognized externally by touching with the hands or seeing with eyes. Therefore, the elements related to shape in this study include not only the appearance of the button of the heater control, but also the position on the operation panel and the inclination of the panel.

3.2 The Summary of Buttons’ Shape and Operation Panel

Figure 14 shows the result of classification about the shape of the buttons in the heater control and the operation panel. From the photographs of various heater controls, after classifying the buttons with different shapes by function, we classified again by the operation method.

Fig. 14.
figure 14

result of classification about the shape of the buttons in the heater control and the operation panel

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The three types of operation panels that have the base structure summarized from the photographs of many operation panels are shown on the right side of Fig. 8. By adding changes in inclination, bulging, dents and so on to these three types, it can become structures of others operation panel.

4 Future Works

In order to clarify the user’s mental model for heater control, we will continue to do experiment and collect data. The part of the preliminary experiment that have done so far is just to verify the rationality of the experiment procedure, the assumed four scenes and evaluation items’. We are planning to conduct experiments on making the environment during driving from now on, using the LCD screen, connected to the play seat and the handle in the current experimental environment, operate the handle and pedal according to instructions issued on the screen. It is necessary to separate experiment participants according to the frequency of driving a car to analyze On the other hand, a model was made according to the appearance of buttons along with each kind of operation panel made of corrugated cardboard, It is necessary to clarify the influence that the shape element of the button bring to the feeling of operation by changing the position on the operation panel and the inclination of the panel.