How to improve factory operation efficiency with autonomous mobile robots

In order to improve factory productivity, it is very important to shorten the operation time (production volume) of each process on the production line, such as processing and inspection, as much as possible, but another improvement that should not be forgotten is to shorten the time it takes to transport work-in-progress between processes and the time required to supply parts and materials to each process.

Especially in "variable production" where multiple products are produced on the same production line while changing product items frequently, sometimes shortening the transfer time can improve the overall productivity of the production line more effectively than shortening the operation time of each process. This is because the operation time of each process and the types and quantities of parts/materials used vary depending on the product item, so the time required to switch product items (called "switching preparation") will be longer.

Factories need a handling method that can cope with suboptimal utilization and unsynchronized operations

Generally, in production lines that mass produce a small number of items, conveyors are used to automatically transport items between processes. There is a famous story about the modern pioneer "Model T Ford": by reducing the number of cars to one, and moving them on a conveyor while performing assembly line operations, efficient assembly was successfully achieved. Even now, in places such as food factories, continuous production is carried out without stopping the production line using the same method.

If the locations for loading and unloading and the production volume of each process are fixed, it is easy to synchronize the time of work and transportation, so efficient transportation can be performed using conveyors. However, work and transportation often do not proceed as expected. If this happens, the production line will be blocked, and in the worst case, the entire production line must be stopped to wait for the delayed work to be completed.

Since the 1990s, Automated Guided Vehicles (AGVs) have replaced conveyor belts and moved along transport paths guided by rails and magnetic markers, and are now widely used to transport products, parts, and materials during the production process (Figure 1). In AGVs, the transport path during transportation is fixed, but the quantity and time of goods transported can be adjusted relatively freely. Therefore, it is possible to cope with operation delays caused by minor defects in each process. In recent years, some AGVs equipped with arms that can automatically load and unload have appeared. Moreover, in order to welcome the advent of the factory era, it has evolved into a smarter "autonomous mobile robot (AMR)".

Figure 1 AGV and AMR for more efficient and flexible handling

In the production of variants, a method is needed to move necessary items in a timely manner

However, even AGVs may not be able to cope well with variable production. This is because the unit production line suitable for variable production is not compatible with AGV transportation.

In a unit production line, one operator is responsible for multiple processes. Therefore, the frequency of moving work-in-progress can be relatively reduced. However, not all processes can be handled by one person. Although it is rare, there are two operations: carrying out and carrying in. In addition, when changing the production line, the parts and materials required for the production of the next product must be supplied in advance.

Generally speaking, in a unit production line, multiple workstations are arranged in a row and each is staffed with workers to carry out production. Work-in-progress is carried out in a timely manner and parts are replenished according to the progress of each workstation. Therefore, a transportation method that can freely set the place and time of carrying in and out like a taxi is needed, rather than an AGV with a fixed route and operating schedule like a railway or a fixed-route bus. In addition, in a unit production line, since the automated guided vehicle will move where there are workers, it is necessary to achieve high safety that can isolate the transportation route, which is not required for AGV.

As a method of transporting to solve these problems, AMRs that transport items while changing the moving route according to the conditions of places with people have been put into use. AMRs automatically identify the locations of devices that become obstacles in the transport route and store them in advance in the form of a map. During the transport process, AMRs move safely while using sensors to detect the location and actions of people in the factory. Although the driving environment and speed are different, it can be said that it has the same functions as the cars being developed by the automotive industry (Figure 2). It is expected that AMR technology will be used not only in factories, but also in the automatic delivery of goods and mail.

Figure 2: Technology promotion from driverless cars to AMRs to handling robots used outside factories

Predict the progress of future operations and intelligently move the required parts

In transportation methods such as AGV and AMR, how to use them effectively and efficiently has also become very important.

In order to minimize the inventory of work-in-progress, pre-assembly parts and materials, the ideal application is "Just in me", so that it can be transported in time as needed. In addition, when changing the transportation route according to the situation like AMR, it is also important to find the movement route that can be carried in and out in the shortest time. However, with the development of information processing technologies such as and, it is now possible to find the ideal application method while grasping the status of the entire factory.

First, IoT makes it possible to accurately grasp the progress of work at each workstation of a cell production line and the inventory status of parts and materials. Until now, the status has been communicated through summonses called "kanban". By digitizing it, it is possible to detect work stoppages that will occur later based on the factory situation grasped in real time and come up with countermeasures.

In addition, in factories that carry out variable production, the necessary parts and materials have been manually picked from the warehouse shelves according to the production items and loaded into the transport vehicle for transportation. Now, it is possible to refer to the digital kanban information while the transport robot selects the shelves where the required parts and materials are placed, moves them to the place where people are, and delivers them in the shortest possible time.