**2. Background Studies**

#### *2.1. The Conventional Exterior Wall Painting Work Process and the Problems*

According to an analysis based on a field examination regarding exterior wall painting work currently performed in South Korea, the process of the exterior wall painting work can be categorized into the following: (1) preparation work; (2) installation work; (3) painting work; (4) disassembly work; (5) horizontal moving work; and (6) demobilization work. Figure 1 illustrates the detailed work process.

**Figure 1.** Conventional exterior wall painting work process.

To understand the exterior wall painting work currently performed in South Korea and investigate the problems of the current method, a questionnaire including questions related to the following three major aspects (Sections 2.1.1–2.1.3) was distributed to 69 on-site field managers who work for seven construction companies (including both general and specialty contractors) in South Korea.

#### 2.1.1. Aspect of the Supply and Demand of Human Resources

Conventional exterior wall painting work is strongly dependent on laborers, as shown by the ratio of the laborer cost to the total construction cost of 80% [13]. Therefore, the supply and demand of exterior wall painting laborers with good quality and construction speeds are very important factors for completing exterior wall painting work successfully and economically. On the other hand, there has always been a difficulty in the supply and demand of skilled laborers, because of the inherent high risks involved in the exterior wall painting work of high-rise apartment complexes. In the survey, all respondents also indicated that such laborer issues would continue to become much more serious in the near future considering that it generally takes approximately eight to nine years for an entry-level laborer to become a skilled laborer, and there is an undersupply.

#### 2.1.2. Aspect of Productivity and Quality

According to the survey result regarding the productivity and quality aspects of the conventional exterior wall painting work, 57.8% of respondents perceived the following to be the most urgen<sup>t</sup> problems to be solved in the aspects of productivity and quality: (1) a decrease in productivity due to the work done by insufficiently skilled laborers and unskilled laborers; and (2) inconsistent thickness of the painted surface due to manual work and deviations in the workmanship of the labor force, respectively. Most of the survey respondents also answered that such problems are expected to worsen in the future due to aging of the labor manpower and the phenomena of avoiding construction fields among the younger work force of South Korea.

## 2.1.3. Aspect of Safety

Conventional exterior wall painting is a high-risk type of work, in which the work is performed by a laborer while suspended in a hanging scaffold. According to the survey regarding the risk and safety aspects of the conventional exterior wall painting work, 66% of respondents answered that the risk of exterior wall painting work is still very high, and alternatives, such as automation (applying robots), need to be considered in an effort to prevent or minimize deadly accidents that can occur in the exterior wall painting work conducted by labor work force.

#### *2.2. Development Status of Gondola-Type Exterior Wall Painting Robot*

To resolve aforementioned problems, a GEWPro has recently been developed in South Korea for the automation of the exterior wall painting work in high-rise buildings [3]. In this study, the characteristics of the developed GEWPro based on its composition and specifications were analyzed to develop a performance evaluation and LCC analysis model [10–12]. The GEWPro is equipped with the capability for exterior wall painting of apartment complexes as its major function and is supplemented with a function for cleaning the outer walls as well. To perform painting and cleaning work, the GEWPro is composed of four parts—"main body of the robot", "hanger", "paint and cleaning water supply device", and a "controller". Figure 2 shows the composition of the main body of the developed GEWPro, and lists its detailed specifications.

**Figure 2.** Major composition of GEWPro.

#### 2.2.1. Main Body of the GEWPro

The main body of GEWPro consists of a camera, painting tool, robot's arms, winder, suction pan, and a cleaning tool. The painting tool is the main device for performing exterior wall painting work and can carry out the exterior wall painting work through six nozzles that are equipped with an anti-scattering cover. The robot arms of GEWPro were installed to enable the simultaneous painting of the protruding areas and blind spots of the external walls without additional work and could perform the painting work through two nozzles. The suction fan was designed to improve wind resistance performance of GEWPro and maintain a consistent distance between the exterior wall and main body of GEWPro during the exterior wall painting. Using the two suction fans installed in the main body of GEWPro, it is possible to perform stable painting work and overcome protruding obstacles while moving up or down. Winder and endless wires are designed to minimize the risk of falling accidents of GEWPro. In addition, a camera attached to the main body of GEWPro allows real-time monitoring of the condition and painting quality of the exterior wall painting work. A cleaning tool has been designed to clean the outer walls, if necessary, by brushing and washing with water.
