The Role Of Robots In Lean Manufacturing

Published: 13th August 2009
Views: N/A

Introduction

Robots have been an off-the shelf purchase item for the last two decades. More than ever, there has been a push to reduce manufacturing costs by using robots. The cost of common robot models from major manufacturers has plummeted due to large volume sales to automotive OEM's and due to the financially negative impact of competition. The performance and range of applications that robots can be used for has also increased exponentially due to mechanical improvements made by robot manufacturers and technical advances made in controller software. While robots are not necessarily lean in nature, they can be programmed to be part of lean system design and lean manufacturing.



Lean Systems and Robots

Automation systems with or without robots cannot be lean by themselves. Designing the manufacturing system to be lean is the challenge that is faced by engineers today. Some of the factors that need to be taken into account while designing a lean manufacturing system comprised of robots are:

• Line production rate requirement

• Equipment reliability and downtime statistics

• Space availability for robotic operations

• Flexibility of process desired

• Cycle time requirements by station or operation

• Repair time of equipment

• Human machine interface requirements

• Product handling requirements

• Maintenance requirements

• Safety standards and ergonomics guidelines

• Line automation requirements (% Automation Vs Manual)

• Conveyor and other transportation requirements

• Allowable scrap rate

• Budget available for the entire system

• Life cycle of manufactured product to ensure acceptable ROI



Based on some or all of the above factors, robots could be an acceptable automation solution that adds value to the system. While small manufacturing systems can be easy to design with limited need for software based validation, larger systems involving multiple robots, tooling fixtures, humans, etc. need to be validated and optimized prior to system build to ensure that the robotic system behaves as predicted. One tool that is being used heavily in the robotic automation engineering business is robotic simulation software to validate robot reach, robot cycle times, robot motion paths and envelopes, robot positioning within the system, to name a few benefits. Using these simulation tools has helped make robotic systems lean in terms of design and manufacture.



Most production lines are designed to be a cooperatively productive and efficient effort between humans, tooling, robots, etc. While it is difficult to ensure strict consistency in humans, robots and machinery can be programmed to be at their optimized best. An efficient automated robotic station ensures that stations ahead of the line are not tied down ensuring better system performance.



Applications in Lean Systems

Material Handling and Machine Tending Applications

Prior to robots, this was purely a manual task. Operators transporting material from one fixture or machine to the next, waiting on the equipment to finish its task, and then relocation of the processed part or parts to another tool or process fixture; these were some of the most common manual tasks that required several operators to manufacture the product. These material handling and machine tending tasks are now almost always accomplished using robots, especially in operations requiring high speed and accuracy. How does this make the system lean?

• There is no wait time for operators since the robots are performing material handling and their wait times could be absorbed by having them perform additional processing operations if possible.

• The robots have negligible downtime for such production operations resulting in limited production loss versus manual operations which tend to be error prone and inconsistent in terms of production rate, shifts, work breaks, etc.

• Robots are inexpensive to operate in the long run compared to manual labor and the return on investment can be fast based on the demand for the manufactured product.

• Robots are repeatable to a high degree of accuracy which results in lowered scrap parts once the robot tasks are optimized.



Multiple Applications - One Robot

While standard off the shelf robots have one arm to which you can mount tooling, the advent of tool changers and dual equipment end-effector design have helped make robotic operations more flexible and lean in terms of higher per cycle utilization. In the die cast industry, robots are currently being used for material handling parts as well as de-gating and finishing operations like deburring and grinding. In the Automotive industry, robots in body shop applications are in some cases used for material handling of parts as well as welding or sealant application through the use of dual application end-effectors or floor mounted pedestal equipment. In applications involving multiple product models, tool changing equipment can be used for robots to disengage/engage new end-effector tooling. Servo motor driven external axes allow robots to be more flexible by acting as auxiliary axes of motion to ensure maximum robot utilization.



This flexibility that allows engineers to process as many operations as possible within the given cycle time and feasibility constraints helps make manufacturing processes lean. Robot vendors have already developed robots with multiple arm configurations. In the future, these multi-arm robots will be more of the norm with operations that are faster, more efficient and lean.



Robots and Vision Applications

Vision systems are being used in combination with robots to help inspect parts for feature existence and feature sizes. Vision systems are more commonly used on robots to act as dynamic guidance systems that allow robots to vary their motion targets based on vision generated guidance information. Vision technology and robots are a natural pairing and the combination has resulted in making robotic operations leaner than ever before.



Operations such as racking/unracking of parts, part picking from bins, visual inspection of parts, which were normally handled by human operators, are now being performed by robots with higher consistency, accuracy, repeatability and speed due to vision systems used in conjunction with the robots. Finishing operations such as routering, grinding, sealing are now being applied more accurately with fewer imperfections and scrap parts thereby contributing solidly to Lean Manufacturing. In the inspection arena, robots are utilized heavily in Flexible Measurement Systems (FMS). Robots mounted with vision cameras to collect feature information for multiple inspection locations have resulted in a drastic reduction in the number of vision cameras and fixtures required to inspect parts. In the past, the same inspection would have been performed with several fixed vision cameras.

Cooperative Applications and Coordinated Motion

Fixture tooling that is custom designed is part of almost all product manufacturing plants. In some cases where the assembly process allows for a slightly lower level of structural accuracy, robots can be used in place of hard tooling fixtures. Robots with docking end-effectors or "geoend-effectors" allow for reduced tooling content and greater flexibility while maintaining a significantly high degree of accuracy and strength. Many assembly operations like roof assembly in automotive assembly are being done with a robot firmly gripping the roof on the automobile while other robots perform welding operations to assemble the roof to the main auto body. Robots are also used for part transfer between assembly stations instead of transfer equipment like lift and carry systems or shuttles thereby adding to the flexibility of the system.



The latest trend in robotics that is gaining acceptance as a lean process is coordinated motion. In this system, two or more robots are controlled by a single controller which allows for easy communication between robots to simultaneously perform coordinated operations on a single large part.



Robots and Cycle Time

Most manufacturing lines are processed at a high gross production rate while they run at a lower net production rate. While larger corporations can afford this expensive production rate safety factor, smaller manufacturing companies need lines that run almost at max capacity to control equipment costs. Preprocessing of robotic operations prior to system integration can go a long way towards controlling equipment costs. Cycle time analysis of robotic operations using simulation tools is critical to ensure that the system is lean.



Some of the common cycle time issues impacting lean manufacturing are:

• Lack of part inventory for robots causing delays in production

• Unsafe work conditions causing slow human operation in situations where robots and humans work in a cooperative environment

• Poor equipment design resulting in wasted repair efforts

• Bottlenecked stations causing part blocking or starvation at other stations

• Individual robots over cycle causing entire station to be over-cycle

• Wait times on other equipment causing robots to go over-cycle

• Poor processing resulting in work overload on robots, operators or machines

• Poor human machine interface causing delays in manufacturing

• Poor software and controls engineering resulting in inefficient I/O and communication between equipment



In major manufacturing assembly plants, there could be hundreds of robots performing material handling, machine tending, welding, finishing, painting and other assembly operations. Wasted robot motion can cause cycle time issues that can lead to bottlenecks and loss of production. Poor path planning can cause product quality issues that can lead to scrap parts. The cost of lost production is a critical factor in lowering corporate profit. Ensuring that the cycle time for robotic work cells is optimized is very important to the lean manufacturing plan.



Workplace Safety and Robots

One of the primary drivers to automate a process using robots is the safety factor. Most manufacturing operations have a degree of human injury risk. Some simple part transfer operations may be safe for humans to perform while others like unloading parts from a press/die or foundry operations with molten metal are definitely not fit for manual operations. In these cases, robots are invaluable in lowering risk to humans.



An unsafe workplace leads to human inefficiency driven by fear. This in turn leads to lowered production rates and employee retention. A safe and secure workplace helps by improving morale and lowering costs which in turn improves the bottom line. Unsafe working environments can lead to waste in terms of effort and time. For instance, if a robot cell is not guarded properly, operators may take longer to service the station because of fear of injury. Ensuring that robotic operations are analyzed carefully for safety and the proper steps are taken to make the workcell safe is very important to make the system lean.



Conclusion

The above cases are just a few examples of how robots, if used correctly, can contribute to lean manufacturing. Robots help achieve higher production quality at a reduced operating cost compared to manual manufacturing. They help produce more parts with fewer defects using less equipment while maintaining their flexibility for future changes. Their capability is only increasing with time. Major robot manufacturers are regularly upgrading their robots with increased payload capacity, greater accuracy, increased reach and range of motion, speed and acceleration, faster communication with external equipment, better safety features, lower operational cost, to name a few. The most significant impact to lean manufacturing related to robots lies in their ease of use. Programming robots to perform manufacturing operations has evolved into a easy to use PC based process that can be easily understood and applied by engineers as well as skilled trades at the plant floor, thereby helping make model updates, maintenance and robot process upkeep lean.



Founded in 1989, Applied Manufacturing Technologies, Inc. (AMT) is a leading supplier of complete consulting and engineering services, offering single-source engineering solutions to the automation and manufacturing industries. The company's service offerings range from design and simulation to programming, installation and support of industrial automation solutions.



Applied Manufacturing Technologies

website: www.appliedmfg.com

email: jmerhib@appliedmfg.com

phone: 248-409-2100

Report this article Ask About This Article


Loading...
More to Explore