There are many factors that can lead a company to consider implementing a conveyor system into a new or existing process—a need for better or more consistent product quality, higher throughput requirements, and safety concerns, are just a few. But conveyors are complex systems that must integrate with other key components in the factory, whether they be robot cells or manual work stations. I recently spoke with Dan Ertel, Principal Development Engineer for Dorner Manufacturing and Kevin Gingerich, Director of Marketing at Bosch Rexroth, about the conveyor selection process and what technical and non-technical factors integrators and end users should consider.
According to Ertel and Gingerich, the selection begins with an analysis of whether automation makes sense for the process in question. Once a decision is made in favor of implementing a pallet conveyor, both technical and non-technical considerations should drive the selection.
Collins | Linear Motion Tips: What factors help an integrator or end user make the decision to implement a conveyor rather than use manual labor?
Ertel | Dorner: One of the main determining factors on whether or not to install a pallet conveyor is the amount of product you’re turning out on a daily basis. If you’re only producing a few units per hour or a handful a day, it might just make sense to keep a more manual-intensive system in place. Pallet conveyors are ideal for ramping up production, so if you are planning to produce several hundred or more units per hour, a conveyor system would likely be a smart choice.
Gingrich | Bosch Rexroth: Bosch Rexroth uses a tool called the “Lean Production Decision Matrix.” The Matrix plots production volume against product mix to help end users or integrators decide whether to automate or not, and if so, whether to automate just individual processes or an entire manufacturing system. The opposite ends of the spectrum are “low volume/high mix” and “high volume/low mix,” with various permutations in between. In a low-volume/high-mix scenario, generally you are making or customizing a wide variety of products to order, and the volumes for individual products are low enough that investments in automation would simply not be worthwhile. However, if the scenario includes one or more processes that are shared by a large enough variety of those products, you might choose to automate those processes; or if you have a process that requires extremely high precision and repeatability, or is a dangerous process, it might be a good idea to automate that.
Collins | Linear Motion Tips: Once the decision to automate has been made, what are the technical application parameters that need to be addressed?
Gingrich | Rexroth: For conveyor systems, the size and shape of the product you’re moving typically determine the initial choices:
- How wide is it?
- How tall?
- Are there protrusions or accessories that will be added that will require clearance areas or special fixtures?
- Is the assembly top-heavy?
- How heavy is it overall, including the weight of the workpiece pallet and any fixtures?
- Is it a sensitive product that could be damaged during transport?
Answers to these questions will help the integrator or end user determine the necessary conveyor width, the model of conveyor chosen, and the transport medium on which the workpiece pallet will circulate (belt, flat-top chain, roller-chain).
Additional critical parameters may include the available floor space in which the process needs to take place, the desired daily (or hourly) output, which processes will be automated and where will they be located in the transport sequence, differences in product models or variants that will be made on the same system, the ergonomics and quality assurance of any manual processes, and even how to offload finished product and transfer it to packaging and shipping processes. Another important consideration is that the output of the system match customer demand as closely as possible.
Ertel | Dorner: There are several factors to consider prior to specifying a pallet system conveyor. The first key piece of information is the size of the pallet needed to hold the product and which sides of the product will need access during the assembly process. A single strand conveyor pallet system is very flexible going through multiple corners and inclines while remaining on the same belt and is great for smaller assemblies. However, a single strand system does not allow access to the bottom of the product or allow larger products like a twin belt does. A twin belt system also allows for reorientation the leading side of the pallet anywhere in the system through use of a lift and rotate module. This can be important when the assembly is interfaced with a machine and requires a specific orientation.
Product flow is another important consideration when laying out a pallet system. At what location do the pallets need to be diverted off the main line and possibly merged back on? Both the Dorner SmartFlex and Precision Move Systems offer turning corner divert and merge modules while a twin belt system offers a 90 degree lift and transfer in both merge and divert modules.
Another factor that needs to be considered is where the pallets are required to make stops. And if the product being moved is fragile, will it be damaged by a sudden stop? If so, cushioned stops will need to be specified instead of fixed stops. Also shock isolation bumpers built into the pallets will protect fragile products when the pallets accumulate in the system.
If a station requires more accurate positioning, to within a couple thousandths of an inch, then a lift and locate station is required. A manual assembly station may be able to use a simpler stop assembly to hold a pallet in a position. A lift and locate station also has the advantage of isolating the pallet from the conveyor so several hundred pounds of force can be applied downward if required.
The key is knowing this type of information early in the design process so it can be taken into consideration when designing the system. Also the weight of the product and the location of pallet accumulation needs to be factored into the design of the pallet conveyor system. This will help determine where the conveyor breaks will be and how loaded each conveyor will be.
Collins | Linear Motion Tips: What non-technical factors should be considered?
Ertel | Dorner: With pallets, you need to consider how product will be placed on and taken off of them. Will the application involve the pallets being removed from the conveyor completely, or will they remain in place? Also, if the conveyor’s path takes it to an elevated level, guarding or netting should be considered to prevent product from falling if there’s a jam in the system. These are some of the programming considerations that need to be examined during the initial design stages.
From a safety standpoint, professionally built conveyors are designed to have employee interaction with them. There’s not a lot of danger, per se, to working around them. That being said, sound safety precautions still need to be followed: remove loose jewelry when working near conveyors; be familiar with its operation and emergency on/off switches etc. It’s also important to review the safety precautions with machinery and equipment that the conveyors are feeding. Employees need to have a good sense of situational awareness to their surroundings to be safe and productive.
Gingrich | Rexroth: The potential for future re-configuration is perhaps the most important non-technical factor, and one of the reasons that pallet-based, flexible assembly conveyors are widely used in automated assembly operations. Nearly all such systems feature a bolt-together aluminum frame, which can be taken apart and re-configured, expanded, or even recycled if needs change.
Maintenance is a frequently neglected consideration, but a critical one, because well-maintained conveyors can last and last, while still providing the needed performance. Safety is paramount, of course, so users will want to make sure that systems include the proper guards around pinch points, lock-out/tag-out procedures are properly followed, and that all of this is regularly checked as part of routine maintenance procedures.
It’s also important not to forget ergonomics in system design. For manual operations, how are the tools to handle the assembly presented? Are the parts that are needed for assembly supplied within easy reach? Is the height of the conveyor appropriate for your workers, or do you have adjustable stools or platforms for them to use so they do not experience fatigue too quickly during their shifts? Is the area well-lighted? Overall, you want to make sure that you’ve considered everything that could interfere with production, even if it means mounting cup holders to the side of the conveyor so that workers don’t spill their drinks inadvertently on the products they’re making.
Conveyors offer many advantages over manual operations, but their implementation often has to be justified through return-on-investment (ROI) analysis, especially when a conveyor is replacing an existing, manual process. To this point, Gingerich points out, “Any ROI calculations need to be based on the whole system, since the entire system is performing the work that was previously done manually.” This includes not only the initial purchase price and installation, but also operating costs—energy, maintenance, and the cost to stock wear parts. These operating costs are the biggest factor and are often overlooked. Fortunately, automation suppliers have the knowledge and experience to estimate these costs based on the desired duty cycle of the system.