3.1 Customer requirements
To derive the customer requirements, we conducted relevant literature reviews and a traditional layout process analysis through on-site observation. There were 13 factors first derived from this process, and a total of 11 requirements were finally defined as required quality through feedback from the site managers in general contractors and specialty contractors for structural work.
After identifying the requirements, a questionnaire was conducted to evaluate the degree of importance for each factor. Through an online survey that took about 10 days, 49 completed questionnaires were collected targeted at construction site managers. A total of 42 questionnaires were used for analysis; seven of the completed questionnaires were judged to be unreliable. On average, the respondents had about 18 years of experience in building construction works (Table 1), and most respondents answered that there was a need for automating layout work (90.6% of respondents checked more than 3 points (normal) on a 5-point scale).
Table 2 shows the importance levels for the CRs that converted the average value of each requirement surveyed on a 5-point scale into 100 points. The most important requirement was to secure marking accuracy within the tolerance (CR1), considering the purpose of the layout operation. Next, it was considered important to drive performance coping with site conditions (CR3), keep constant marking quality (CR4), and easy operation and maintenance (CR11). This is believed to be because the robot system in this study should drive and mark in poor ground and working conditions, unlike the systems for interior layout on finished floors.
3.2 Technical characteristics and correlations between CRs and TCs
Related technical characteristics (TCs) were derived through analyzing the 11 requirements. TCs were suggested by the members of the research group based on their knowledge, experience, and relevant documents because they have a high understanding of the operational processes. The robot system can be largely divided into driving, marking, and power supply units, and 16 technical factors required for each unit and robot design were derived to satisfy the customer demands.
Next, the correlation between CRs and TCs was derived through a group meeting of the task-force team to prioritize impacts of the TCs on achieving customer needs. The strength of the relationship was assessed with values of 1 (possibly correlated), 3 (moderately correlated), and 9 (strongly correlated), as proposed by Cohen [7]. As shown in Table 3, movement control (TC6), marking control (TC11), and sensing (TC12) devices have correlations with the largest number of CRs. Movement control and sensing devices have high correlations with the demands of CR3, 8, and 9, while marking control devices have high correlations with CR1, 2, and 4.
To quantify the importance of each technical factor, absolute weight (AW) and relative weight (RW) were calculated by equations 1 and 2, respectively. From the AWs and RWs, the prioritized TCs are concerned with component control and sensing. Movement and marking control and sensing devices reflect about 31.7% in the design of the layout robot. Next, important technical factors were shown in the order of ink supply device (TC10), robot weight (TC3), and marking speed (TC9). The presented six factors contribute more than 50% of the total RW and thus were selected as key TCs to propose innovative solutions while meeting customer demands.
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)
3.3 Contradiction analysis
Technical correlations in the roof of the HOQ were derived from the task-force team of the research group to identify design bottlenecks. In this study, the interaction between TCs was represented as symbols + and –, indicating positive and negative correlations, respectively (Fig. 2).
Highly important technical factors, including TC6, TC11, and TC12, mainly showed negative correlations with speed (TC4, TC9), weight (TC3), size (TC2), and/or battery capacity (TC15). The negatively correlated TCs are described as technical contradictions reflecting the requirements, as follows: (C1, C2) For easy and accurate control while coping with uneven ground conditions, movement and marking speed should be slowed; (C3) To ensure precise marking and sensing performance, the complexity of equipment increases, resulting in an increase in battery consumption; (C4) For various types of marking while maintaining marking quality, the volume of the robot system should be increased.
Among six technical factors, the factors with technical contradictions between them were set as the improving factor for the characteristics with higher weights. In addition, battery capacity can be improved while reducing the complexity of the system, which is excluded from establishing contradictions. The presented four contradictions should be transformed into technical parameters in TRIZ. The improving and worsening features were converted into highly relevant parameters to use inventive principles in the contradiction matrix, as shown in Table 4. Each solution principle number in Table 4 indicates one of the 40 inventive principles proposed by Altshuller [6].
3.4 Problem-solving ideas and design alternatives based on the inventive principle
Among the invention principles corresponding to each contradiction, one to two invention principles that fit the design of an automated marking robot were used to derive problem-solving ideas. The ideas were derived through analogy thinking by referring to the conceptual solutions provided by inventive principles. For example, to resolve the C3 contradiction, a conceptual solution using the principle of “prior action (10)” was derived: “Place objects in advance so that they can go into action immediately from the most convenient location.” With reference to the solution, the idea of “replacing sensing devices for precise measurement and control by inputting the location of obstacles in the drawing in advance” was derived. The problem-solving ideas for other contradictions were derived by the same principle and process, as shown in Table 5.
The presented ideas were organized and integrated to derive design alternatives for marking robots. First, they can be distinguished by the driving and marking operation method. The first method is to separate the robot’s driving and marking (idea A). The robot performs the marking operation while it is stationary, increasing the speed of movement by decreasing the positional precision when operating the robot. On the other hand, the second method is to enhance the overall speed of work by performing marking operations while the robot is running (idea D). This approach requires a relatively low speed of movement of the robot and minimizing marking lines to secure marking accuracy.
Next, the ideas are classified by the marking method. First, the printer head of the noncontact type from the floor integrated with ink supply unit moving on a single axis (ideas I and O) can be applied. This can print various types of marks including lines, texts, and symbols while requiring a supplementary device to maintain a certain distance from the floor surface. Second, a method of drawing a line of constant length through marking the head of a bar type (idea J) can be applied. These types of marking methods are suitable for operating the robot separately from marking and driving. On the other hand, in the operation method of marking and driving simultaneously, a point-by-point marking method such as a cross (+) shape (idea H) can be applied instead of lines at regular intervals to secure precision in marking. Regardless of the marking method, the marking head shall be exposed to the outside of the robot body to perform marking adjacent to rebars protruding over the floor and installed on one side of the robot body for easy control (idea C). In addition, for driving wheels, the two-wheeled steering drive system with suspension devices (ideas B and E) and one- or two-wheel caster is adopted for efficient movement and rotation in narrow spaces as well as improvement of driving performance on uneven floors.
As a result, three design alternatives are derived through the combination of robot operation and marking methods, as shown in Table 6. Regardless of design alternatives, the robot’s position and orientation can be accurately calculated through a movable prism target installed on the top of the robot body and tracking of the total station (idea G). In addition, the location information of fixed obstacles on the robot’s driving path can be inputted in the drawing in advance (idea K), and the avoidance path can be generated to replace the expensive sensing device for precise recognition.
3.5 Evaluation of alternatives and selection of optimal robot design
A quantitative assessment was conducted to select an optimal design solution among the three alternatives. In general, the usefulness of solutions is assessed through comparisons with existing systems that are subject to improvement. However, this study used comparative evaluation among the alternatives because it is not intended to improve existing systems. Six evaluation criteria were first set based on the user requirements that are highly correlated with the key TCs and of high importance, and the weight of each criterion was calculated from the importance value of the requirements being targeted. The degree to which each alternative meets the established evaluation criteria was derived on a five-point scale through consultation between the task-force team members. The final performance score of each alternative was calculated by multiplying the weight by the corresponding score of each criterion and then adding it together.
As a result of the evaluation, the first alternative to marking using the noncontact type of printer head while stationary was selected as the optimal design solution with a score of 4.17 (Table 7). The third alternative was best evaluated in terms of duration reduction on marking work, but the complexity of algorithms for position calculation and control of the robot increases and additional devices are expected to be needed to secure marking precision. In the case of the second alternative, it is possible to mark only a line shape of a certain length by stamping the bar type marking head. Thus, the performance in terms of the variety and quality of the marking was assessed to be relatively poor.
It was evaluated that with the first alternative, it was possible to secure excellent performance in terms of marking precision, which is the most important requirement, as the printer head moves and marks uniaxially along with an auxiliary device to maintain a certain distance from the floor in a stationary state. In addition, unlike other alternatives, it was evaluated excellently in terms of being able to mark various types of lines, symbols, and texts. The complexity is minimized by configuring the device to enable marking through direct jetting from the ink cartridge without a separate supply unit, and it is possible to secure the diversity of marking colors more easily by allowing only the cartridge to be additionally attached depending on the situation. Figs 3 and 4 show the concept design of the robot and operation process based on the first alternative, respectively.