Through the years, the use of mother-daughter cart solutions in conjunction with vision guided vehicles (VGVs) has become more widely recognized, and for many applications is considered to be a Lean best practice.
While many users documenting the successful implementation of such as system could list the benefits unique to their specific application, there are three key advantages evident across the users of these systems: improved safety, inventory reduction in the assembly area, and improved material handling efficiency.
The term "fork truck free" (or better stated as the initiative toward increasing fork truck "effectiveness") has become the first initiative for many facilities beginning their Lean journey. Primary motivators for this initiative are often not only efficiency related, but are also tied to an objective to improve safety in the workplace. The fact is, any time heavy machinery (for the sake of our discussion - fork trucks and/or tuggers) is operated manually, the potential for human error leading to personal injury or product damage is present. Extensive case studies support that the installation of VGVs in conjunction with mother-daughter carts significantly reduced personal injury and damage to product. VGVs allow material movement to be predictable, dependable, and also available in environments that may not be suitable for operators for safety reasons. Recently, the installation of a VGV into a painting operation addressed safety concerns by allowing the VGV guided mother-daughter cart system to travel with a train of material through production areas that were unsafe for human driven traffic. Given the accuracy in which the VGV system is able to function, the route was timed to function in concert with the conveyors and travel closer to the production line than the previous manual route. The end results were: efficient movement of parts through a paint operation without safety concerns, recognized space savings in the plant, and reduced part damage.
There are many "wastes" to consider when evaluating the efficiency of a production system—time, space, effort, and inventory are just a few. They are all measurable, and all directly affect profitability. While maintaining adequate inventory is a requirement for production, too much inventory in the production area perpetuates other wastes. Work areas become cluttered, physical effort and steps are wasted to support production, and there is increased opportunity for error. Using a VGV and mother-daughter cart delivery system facilitates options for materials to be stored off-line, often in a supermarket style area, where they can be loaded and sequenced or kitted to support production. With this method, items can be brought to the line on a schedule, in sequence if required, and presented in the best ergonomic location, without a material handler transporting them. If materials can be replenished and displayed in rack or cart form, consider replacing your existing layout with a mother-daughter cart system and use a VGV to run the delivery route.
While moving inventory off-line is a way to save space and add error proofing to a process, it is often viewed as inefficient due to the distance required to transport materials (non-value-added activity) back to the work area. Having a material handler transport these parts from one area to another is not an efficient use of time and resources. However, utilizing a mother-daughter cart with a VGV to transport parts reduces the waste of human effort. Mother-daughter cart designs allow for carts to remain coupled while unloaded, which is more efficient than cart only trains that require manual effort to decouple carts and replenish line side inventory. When unloading is complete, the train can be sent back to the supermarket area to be loaded for the next supply run. These VGV guided cart systems are dependable, so operators quickly adapt and support them as welcomed additions to the team.