Kaizen of panel replacement work process utilizing simulation and virtual environmentKaizen of panel replacement work process utilizing simulation and virtual environment

March 28, 2022

Using Simulation to Improve Conditions for Construction Workers
- Reducing Construction Time through Kaizen PART 2 -

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  • SDG ICON. Goal 8: Decent work and economic growth
  • SDG ICON. Goal 17: Partnerships for the goals

Toyota Motor Corporation’s Frontier Research Center has been working to develop construction methods for wall-mounted solar panels (photovoltaic, or PV panels) as one aspect of its research into innovative infrastructure technologies. This time, with the completion of verification evaluation of PV panels on the Tokyo Metropolitan Expressway, work was fulfilled on the walls to restore the original sound barriers (Image 1). In this article, by getting back to the basics of Toyota's Kaizen, which is “To improve conditions for workers,” we will discuss Kaizen (improvement) activities undertaken by Obayashi Corporation (Obayashi) and Toyota Central R&D Labs, Inc. (TCRDL) for this project.

  • Steps in panel replacement work
    Image 1 Steps in panel replacement work

How Kaizen Improves Conditions for Workers

Q. What actions did you take to improve conditions for workers?

Sakai: First, as previously, we looked at improving the operation efficiency. For this work, we again jointly developed panel replacement equipment with Obayashi, but for the Kaizen, we were conscious of considering smooth-flowing work processes.

This involved reorganizing the work content and procedures so that, as much as possible, workers can continue working uninterrupted. With driving a car, for example, with of a road that facilitates good traffic flow, it is possible to continue driving at a constant speed with lower chance of getting caught in a traffic jam or stopping at a red light, making it possible to reach the destination sooner, with improved fuel efficiency. Essentially, improving the flow reduces time wasted, which leads to improved conditions for workers.

Q. That may be so with cars, but “workers can continue working uninterrupted” does not sound like improved conditions, instead, wouldn’t it increase their physical burden?

Sakai: Certainly with manual labor requiring handling of heavy objects, it’s impossible to keep working without a break. On this occasion, we identified work that was physically laborious, and strived for Kaizen of such work processes, achieving improvements that allowed workers to handle work with reduced physical burden. We also set working hours to seven hours or under per day, excluding breaks.

In essence, these initiatives aimed to create an improved process whereby there were no impediments to working for a certain period, while reducing physical burden and incorporating recovery breaks. In terms of the example of cars I gave earlier, it’s possible to arrive faster and more comfortably at the destination, with the time to take a rest before the next scheduled activity.

Simulation to Consider Panel Removal

Q. Can you explain how you used simulation to implement Kaizen in the removal process?

Sakai: To put it simply, we simulated the construction work on the Tokyo Metropolitan Expressway virtually.

The biggest issue with this process Kaizen was that, unlike production line infrastructure at plants, we did not know the conditions at the removal work site where we wanted to implement Kaizen until the day of work.

In a plant, it is possible to actually observe the work, see with your own eyes what the problem is, consider Kaizen proposals, implement them and verify the results. But that is not possible with construction work. Consequently, because we discussed much of the work based on our assumptions, and when we could only share fragmentary diagrams and words, it was very difficult to share information accurately within the team.

Therefore, we reproduced a part of the Tokyo Metropolitan Expressway virtually to check the work flow, whereby we were able to advance verification of the results of our Kaizen.

Q. You undertook repeated Kaizen using the virtual work site! Can you describe the virtual simulation in more detail?

Sakai: To begin, we recreated the visual aspects, such as the topography, structures, and construction machinery, using 3D CG1. The focus of this Kaizen was the workers’ way of working. To this end, we also recreated the workers virtually to visualize how they work in cooperation with other workers and machinery in this environment.

As a result of the simulation, we realized that, using the conventional equipment, the workers who were replacing the existing PV panels with the sound barriers, and the workers who were drilling holes in the pillars, were waiting for the other to finish their work, resulting in an inefficient work process.

Using the simulation (Image 2), we were able to confirm that, by enlarging the equipment, both parties could work simultaneously, reducing waiting time. Then, we asked Obayashi to produce a prototype of the larger panel replacement equipment incorporating our knowledge. (Please see Obayashi’s related release for a prototype of the larger panel replacement equipment on (Japanese Only))

  •  Comparison of waiting time before and after Kaizen
    Image 2 Comparison of waiting time before and after Kaizen

Q. So, you were able to improve the work flow through Kaizen. What kind of virtual simulation did you use to promote Kaizen of the physical burden?

Sakai: In order to verify whether a process was physically strenuous, we quantified the muscle fatigue. This concept of “fatigue” was an important point in this initiative.

Even without a heavy load, workers may get fatigued through repetition of light tasks, and even if they are exhausted, it is possible to resume work after a rest. In essence, the way exhaustion arises varies for the same work according to the order and timing.

We collaborated with TCRDL to introduce a “muscle fatigue model2,3 that took into account accumulated fatigue and recovery. When we calculated the degree of fatigue for the task of drilling holes in the pillars, before Kaizen, workers were still forced to wait for long periods even after recovering to some extent. But we learned that by only improving the work flow, workers were unable to get sufficient rest and the physical burden had worsened.

To rectify this, we introduced new equipment to assist with time-consuming marking work (marking the points for drilling holes in the pillars) and the physically demanding work of positioning the tools, and thereby improved the nature of the work. As a result, we not only managed to reduce the physical burden on workers, but also reduced the work time, which helped to secure time for recovery (Image 3).

  • Physical burden of drilling holes in pillars and recovery
    Image 3 Physical burden of drilling holes in pillars and recovery

As a result of advancing Kaizen of work processes, in simulation, we managed to reduce the time required for the panel replacement cycle, which was initially 14 minutes per panel (6 minutes of work, 8 minutes for recovery). Eventually, the replacement time was 8 minutes (5 minutes of work, 3 minutes for recovery. (See video.)
Following the Kaizen, the workers involved gave positive feedback, commenting that work was easier, less exhausting than with the old method, and that the work flow had clearly improved.

Future Prospects

Q. Finally, can you tell us about the future prospects?

Sakai: Because the muscle fatigue model and work simulation that I discussed earlier are still under development, we only tested it on comparatively small-scale construction. In the future, we hope to collaborate with various companies and researchers, increase the accuracy of simulation technology, and propose the Kaizen that is close to workers to apply it on larger-scale construction and to achieve more precise Kaizen.

  • PV panel replacement project member from Obayashi Corporation, Toyota Central R & D Labs., and Toyota
    Image 4 Project members (the author is in front row, third from the right)

Author: Noriaki Sakai
Assistant Manager, Infrastructure System Group No.2, R-Frontier Div.
He had previously been responsible for mechanical design and assessment of partner robots, as well as data analysis of production facilities. For this project, he was involved in planning and implementation of the simulator.


3D computer graphics
Utilizing the model of Frey-Law et al.
Ting Xia, Laura A. Frey Law, "A theoretical approach for modeling peripheral muscle fatigue and recovery", Journal of Biomechanics, 41(2008), pp.3046-3052.
John M. Looft, Nicole Herkert, Laura Frey-Law, "Modification of a three-compartment muscle fatigue model to predict peak torque decline during intermittent tasks", Journal of Biomechanics, 77(2018), pp.16-25.

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