Designing automation systems to be lean is one of the largest challenges faced by engineers today. When designing a lean, robotic assembly system, engineers should consider the following factors:
- Allowable scrap rate.
- Conveyor and other transportation requirements.
- Cycle time requirements by station or operation.
- Equipment reliability and downtime statistics.
- Flexibility requirements.
- Human machine interface requirements.
- Product life cycle.
- Automation requirements. (How much of the process will be automated and how much will be done manually?)
- Production rate.
- Handling requirements.
- Maintenance requirements.
- Repair time of equipment.
- Available floor space.
- Safety standards and ergonomics guidelines.
- Number of product variants.
Traditional assembly lines are designed to be an effective collaboration between man and machine. While the machines (including robots) can be programmed for optimal performance, people cannot. When designing lean robotic workcells, engineers must account for the “human variable” by ensuring that each station in the line is capable of consistent performance.
Most importantly, the use of robots must be justified by a return-on-investment (ROI) analysis. Robots can significantly improve the ROI in a manufacturing environment, especially when they are implemented in support of a lean initiative, but again, planning is critical. The robots must be incorporated into an overall lean environment to get the desired results.
Robots in Lean Systems
Prior to robots, material handling and machine tending were purely manual tasks. Operators would transport material from one fixture or machine to the next, wait for the equipment to finish its task, and then relocate the part to another tool or process fixture. Several operators were usually required. Today, these labor-intensive tasks are often accomplished using robots, especially in operations requiring high speed and accuracy.
Robots are also playing a role on packaging lines. For example, food manufacturers are increasingly using robots to handle all their back-end processes. Robots pick goods from a conveyor and place them into packaging. Another robot places the packages into cases, and a third robot places the cases accurately on a pallet.
The inherent flexibility of robots gives food manufacturers the ability to meet varied customer demands. For example, Walmart may have a different packaging and palletizing requirement than Costco or Kroger. With robotics, each order can be picked, packaged and palletized automatically to meet each customer’s requirements.
How do robots make such applications lean? For one, there is no wait time for operators. A material handling robot can be set up to multitask, performing additional processing steps between operations.
Robots have negligible downtime. Robots deliver a limited production loss compared with manual operations, which tend to be error-prone and provide inconsistent production rates.
Robots are less expensive to operate, compared with human labor—especially when overtime is required. Robots’ ROI can be quickly realized when there is high demand for the product.
Robots are capable of highly accurate, highly repeatable tasks. Once the application has been optimized, robots produce little or no scrap.
Robots do not get fatigued. Their performance is not compromised by heat, dust, humidity and other challenging work environments.
Many Applications, One Robot
When incorporating robots into a lean environment, engineers should try to integrate as many operations as possible within the given floor space.
Standard robots have a single tool mounted to a single arm, which is more efficient than human labor, but limiting due to the lack of flexibility. Today’s robots can incorporate tool changers so the robot can handle more than one task. With one robot able to perform multiple functions, the manufacturer will see improved utilization and a faster ROI.
In the die cast industry, robots are commonly used for material handling, degating, and finishing operations, such as deburring and grinding.
On automotive body lines, robots are often used for material handling, welding and sealant application. Robots that need to perform more than one function are equipped with tool changers so they can swap out end-effectors on the fly. Mounting the robot to a servo-driven linear axis allows one robot to tend multiple machines or work on extra-large assemblies.
While single-arm robots dominate today’s manufacturing landscape, multiarm robots will become the norm in the near future.
Robots and Vision
Vision technology and robots are a natural pairing. Vision systems are commonly used to allow robots to vary their motion targets based on vision-generated guidance information.
Operations that required making visual distinctions and decisions (such as racking and unracking of parts, part picking from bins, and part inspections) were once exclusively handled by people. With vision guidance, these same tasks can be performed by robots with better consistency, accuracy, repeatability and speed. Vision-equipped robots can also reduce imperfections and scrap material in finishing operations, such as routing, grinding and sealing.
In the inspection arena, robots are used heavily in flexible measurement systems. Robots equipped with vision cameras can collect information from multiple locations, dramatically reducing the number of cameras and fixtures required to inspect parts.
The latest trend in robotics is coordinated motion. In such a system, two or more robots are governed by a single controller. The controller allows for easy communication between robots so they can simultaneously perform coordinated operations on a single large part. Coordinating robot movements can significantly reduce the time wasted in the manufacturing process.
In the automotive industry, roof assembly is now commonly performed with one robot gripping the roof, while other robots weld it to the car body. Robots are also used to transfer parts between assembly stations instead of dedicated equipment, such as shuttles or lift-and-carry systems.
Custom tooling is required in almost every assembly plant. If the assembly process allows for a slightly lower level of structural accuracy, robots can be used in place of hard tooling. Robots with docking end-effectors or “geo end-effectors” reduce the need for custom tooling and provide greater flexibility, while maintaining a significantly high degree of accuracy and strength.
Robots and Cycle Time
Major assembly plants often have hundreds of robots performing material handling, machine tending, welding, finishing, painting and other operations. Wasted motion in any of these applications can cause cycle time issues, creating bottlenecks and loss of production. Poor path planning can also lead to quality issues.
Optimizing cycle time in robotic workcells is critical for lean manufacturing. Some common cycle time issues include:
- Lack of part inventory.
- Unsafe work conditions, causing workers to slow down when working in close proximity with robots.
- Poor equipment design, resulting in frequent downtime.
- Poor human-machine interface.
- Poor software and controls engineering, resulting in inefficient I/O and communication between equipment.
- Detailed planning of robotic operations prior to system integration can go a long way towards controlling equipment and labor costs.
Workplace Safety and Robots
Most manufacturing operations have a degree of injury risk. One of the primary reasons to automate a process using robots is to improve workplace safety. High-risk tasks, such as unloading parts from a fast-moving press or working with molten metal, are definitely not suited for people. In these cases, robots are invaluable in lowering the risk of injury or death.
An unsafe workplace leads to fear-driven human inefficiency, lowered production rates, higher insurance and workers’ compensation costs, and high employee turnover. Conversely, a safe workplace boosts morale, increases employee retention, and lowers costs.
Robots can make the work environment safer by performing tasks that are unsafe for humans, but robots themselves can be unsafe. For example, if a robot cell is not guarded properly, operators may take longer to service the station because of fear of injury. Wherever robots are used, the environment must be carefully analyzed and proper protocols instituted to keep the workcell safe. If the employees don’t feel safe, the workcell will not be as lean as designed.
Many applications require the strengths of both people and robots, but until recently, this could be very dangerous. Now, specialized software can allow robots and operators to collaborate much more closely without compromising safety. This technology combines the flexibility of human interaction with the precision and handling capacity of robots to make applications lean, accurate and safe.
If used correctly, robots can enhance a lean manufacturing environment. Robots offer speed and accuracy that can’t be achieved with human labor. Robots can also reduce operating costs, decrease scrap and increase flexibility. Few other manufacturing technologies can reduce waste as well as robots.
The capabilities of robots have only increased with time, while their costs have continued to fall. Robot suppliers are constantly upgrading their products, giving them increased payload capacity, greater accuracy, increased reach and range of motion, improved speed and acceleration, faster communication with external equipment, better safety features, and lower operational costs.
If you have not explored incorporating robotics into your manufacturing environment lately, it’s time to take another look. Robots promise better quality, reduced costs, less waste, and a fast ROI.