Information technology, the worldwide web, and rapid product development -- they all challenge manufacturers to deliver an ever-faster response to changing market demands. One solution that has experienced renewed popularity is the manual workstation. Pick light (curtain) automation allows a prosaic manual manufacturing platform to meet ever-varying and fast-changing customer needs, while still improving manufacturing profits.
Portable, manual workstations have become popular in the U.S. and have been adapted to handle a growing list of assembly demands, such as variations in product sizes, worker ergonomics and flexibility, portability and even application-specific operating environments. (See sidebar, below, for more on the changing automation equation.) Even large companies like General Motors use operator workstations in assembly operations.
As a workstation''s capabilities expand, they, in turn, place greater demand on workers and supervisors who use them. They have to make manual assembly even more productive and more responsive to rapidly changing customer demands. Recently, attention to assembly productivity has moved from the workstation to its component parts and bins, as well as to the support issues similar to those associated with any other piece of equipment.
Low training and setup times -- once workstation advantages, when assembly tasks were simple -- have taken on more significance as workstation assembly tasks become more extensive and sophisticated. As a result, simplifying and speeding worker training and setup has become a focus of workstation development.
A Guiding Light
Part selection and verification scanners (see sidebar, below, for more) present a simple solution for meeting a manufacturer''s numerous assembly needs. Called "pick-to-light," this technology simplifies part-picking procedures by aiding workers with visual indication and feedback, eliminating wasted motion, and error -proofing assembly operations. It also reduces problems caused by the tedium workers encounter in their workday.
As a result, it plays a role in improving assembly speed and product quality, and lowering costs, including inventory, line changeover and setup, and worker training.
As new generations of workstations deliver production flexibility and throughput, the demands on the people manning them also increase. People are not machines, and even the best and most conscientious workers will tend to make assembly errors and generate product quality problems. The result is rework, or sometimes, the necessity of scrapping the product -- a condition that costs more to fix the later it is detected in the production cycle. These problems become even more acute when assembly components have a similar look and feel.
A light source with a feedback mechanism placed in front of a pick-bin works as an error-checking and correcting mechanism. It also eliminates the need to read a paper list to figure out where the right part is located.
One such part selection and verification scanner is available from Scientific Technologies Inc. The PartScan Series PS7600 looks like a mini safety light curtain. (NOTE: It does not include the requisite safety circuitry and must not be used for personnel protection [safety] applications.). The PartScan can be mounted on just about any rack, bin or shelf, and on static bins or carousels.
The PS7600 Series PartScan belongs to the pick-to-light general class of products that not only verifies correct part-picks, but also guides workers through the part picking process. This enables manufacturing engineers to control the selection of a larger number of parts at a workstation.
To help the worker, selection and verification scanners include bright LED light sources mounted on the front of each of two columns holding the infrared transmitter and receiver detector. The scanner can be programmed to turn the lights on in sequence moving up or down; or moving from the ends to the center; or flashing on-and-off in unison to indicate the appropriate bin.
The worker responds to the indicator lights by picking a part from the bin. Breaking the scanner''s infrared beam mounted in front of the bin signals the controller that the appropriate pick has been accomplished. The controller then activates the next scanner display to indicate the next bin pick until the cycle is completed. The interaction between the worker and the controller determines the pace of the assembly operation.
If the worker breaks the scanning beam in front of the wrong bin, the controller will indicate a fault by initiating an alarm, such as a flashing light and a buzzer or other audible indicator, until the correct pick is made.
Most part selection and verification scanners, including STI''s PartScan, work with any type of controller that can handle contact closure I/O, typically a programmable controller (PLC) or personal computer (PC). An engineer simply programs the sequence of the pick and alarm conditions for the assembly process. Modern programming techniques allow the user to load pre-configured assembly programs to speed setup and changeover.
Leveraged Benefits
Adding bin-pick feedback, such as the PartScan, delivers multiple benefits both during and before the assembly process. The more direct benefits during assembly are increased operator speed and throughput, as well as production quality. Simply activating an indicator light in front of a bin or box eliminates the worker''s requirement to figure out where the next part bin pick occurs. This simple workstation enhancement significantly reduces the time between part picks and speeds assembly. Sources estimate that pick rates can double or triple when utilizing pick-to-light technology. This becomes more important as workstation assembly assignments become larger and more complex.
In a similar manner, adding pick-to-light technology works to improve assembly quality. Picking the right part and putting it in the right place eliminates two sources of potential assembly quality problems.
Although a product like the PartScan cannot guard against picking incorrect parts mixed in the wrong bin or box, it still produces significant improvements in assembly quality. Users of such equipment report low assembly error rates -- typically less than 1 per 10,000 picks, with some error rates said to drop even lower.
The addition of pick-to-light technology also reduces production line downtime. Worker training and startup times are minimized. The company loads the assembly program and verifies bin placement. Experienced workers don''t need to figure out where parts are stored for a new production run, and need little or no training to start a new production run.
In some applications, it reduces worker training for a new production run and workstation setup. Pick-to-light systems have even proven valuable in kitting parts and components for workstations by allowing support workers to place the right tools and parts in a box for a new assembly assignment.
Sidebars -- For Additional InformationVerified Actions Improve Quality Equation
The action of breaking scanner beams serves to indicate whether an action is taken and is correct. This function alone will reduce quality costs by indicating an error before it occurs. This keeps corrective actions close to the source of the problem where it is least expensive to fix. Eliminating defects at the source improves both productivity and quality.
Eliminating assembly errors cuts the labor, additional materials and administrative costs associated with a corrective action. In addition, the simple act of pick verification also reduces warranty costs and reduces the probability of delivering a bad product to customers -- the ultimate quality defect.
A New Perspective On the Automation Equation
Manual workstations make sense where labor is cheap -- they play a significant role in determining the required level of automation. However, additional business factors -- time-to-market, short lead times, and high mix/low volume production runs -- may also favor manual workstations. In still other scenarios, transportation costs and time delays, or a production line''s setup time, make workstations a viable option. The difference may be between five minutes with pick-to-light compared to an hour or more without the technology.
Besides time to market, smaller companies, which must support dozens of options and short production runs, have found value in workstation technology to improve assembly efficiency and productivity. They have become popular in lean manufacturing work environments.
PartScan and Verification
The principle of pick-to-light shifts responsibility of selecting the right parts in the correct sequence from the operator to an automation controller, such as a PLC, which accurately controls the correct pick using a verified sequence program. An indicator light on the part scan alerts the operator as to which part bin to select. The PartScan detects when a worker selects the part when any one of its five infrared beam paths is broken.
Detecting the proper selection, the PLC will then light up the next bin pick. If the beams in front of the wrong bin are broken, the PartScan sounds an alert enabling workers to take corrective action immediately.
Workstations Evolve to Meet Increasing User Needs
Although manual workstations and their accessories have been around for decades, their designs have gone through numerous changes, and continue to develop a proliferation of options to offer increased flexibility and productivity options.
Starting with a basic work surface design and adding options to hold tools and parts in convenient spaces, the workstation has added pneumatic controls for height adjustments, as well as adjustable accessory add-ons that allowed different-sized workers to use the same workstation in comfort.
The workstation concept then changed to include the volume around the work surface and took on greater importance to the total assembly equation. Tools, lift tables, chairs, footrests, and fixtures were placed in strategic ergonomic locations.
Workstation developers studied operators and their interactions with part bins and tools. They asked: "How do we get better productivity and efficiency from a workstation?" With each new generation of workstations, companies and manufacturing engineers became accustomed to expecting increased functionality and capability.
Application-specific workstations were developed to handle specific assembly requirements with custom solutions. Electronics assembly demanded workstations that used electrostatic dissipative (ESD) technology and a confined work envelope.
Other workstations had designs to meet clean room requirements or included heavy-duty components to handle assemblies for automotive, truck and off-road equipment subassemblies. Of course, this assembly work was all done in a safe and healthy workspace requiring additional safety add-ons.
Workstation designers eventually refined the meaning of fast and flexible assembly at a workstation to include fast changeovers for new production runs. They also looked at using multiple workstations in a flow cell assembly line.
Now, not only must workstations work as modules changing with each production run, but each workstation must also handle multiple operations to minimize product and material handling. Extra handling contributes both to production cost and increases the possibility of introducing product damage or defect.
Users now expect that each new generation of workstation must handle and incorporate new and varied workstation concepts. The latest generation of workstations uses light-guided and worker-detection technology to improve the speed of worker training, production support and quality concerns as greater expectations are heaped on the once humble workstation.