The roots of error-proofing can be traced back to product-quality guru Edward Deming. Deming introduced his principles of improving product quality and design to the United States in the 1940s, although they gained greater favor in Japan in the 1950s. A short time later, Shigeo Shingo made known the Japanese concept of poka-yoke (pronounced POH-kah YOH-kay), or mistake-proofing.
“Back then, fastening error-proofing in the U.S. was done by many inspectors on the production line,” says Michael Poth, director of marketing for Stanley Assembly Technologies. “Countless error-proofing improvements have been made since then to take the variables out of the fastening equation.”
Poth provides the following timeline of error-proofing improvements over the past 50 years or so:
1950s: Fastener assembly is dominated by Yankee screwdrivers, ratchet wrenches, stall-type air tools and pneumatic impact wrenches. Electric tools are predominantly used for drilling and grinding.
1957: First "Shut-off" tool is introduced. The air supply to the motor was shut-off when clutch released at predetermined torque. Because the shut-off feature reduces operator influence on torque control, shut-off tools eventually become known as "Torque Control Tools."1962: Thor Tool Co. introduces an impact wrench with a hydraulic impulse mechanism The hydraulic pulse unit makes a "softer" impact wrench. This was a precursor to the later day impulse wrench.
1966: Stanley introduces the T shut-off assembly tool, which used a simple spring-loaded air valve to shut off the motor air supply when the motor pressure reached a predetermined value.
1968: GSE introduces offers a rotary torque transducer, which allows very accurate dynamic torque measurement.
1969: Ford Motor Co. begins measuring torque performance of assembly tools. The company discovers torque value is greatly influenced by the joint and begins testing assembly tools on a wide range of joint torque rates.
1970: Ford establishes the Certified Tool Program and the Power Tool Manual, as well as torque control targets for acceptance into the Power Tool Manual.
1974: Ford recognizes common practice by tool operators of tampering with assembly tool torque adjustment settings. Ford aAsks tool manufacturers to remove torque adjustment from the tools.
*Stanley introduces TA shut-off assembly tools, which allow torque to be adjusted via remote pressure regulation.
1976: Sanyo introduces DC electric assembly tools to Japan’s automotive industry.
Late 1970s: Japanese assembly plants start using DC electric tools and pneumatic impulse wrenches in tandem with click wrenches for fastener assembly.
1981: Uryu (Japan) introduces pneumatic impulse wrench to US through Japanese transplant auto plants. GM's partnership with Toyota (Nummi) initiates widespread use of these tools throughout GM assembly plants. Ford doesn't approve them for use in their plants because of poor torque control.
Early 1980s: Assembly tools with integral torque transducers are introduced. The tools allow direct measurement of dynamic torque during the assembly process.
*Chicago Pneumatic, Ingersoll Rand, SPS and others begin to offer DC electric tools for threaded fastener assembly. Automotive engine assembly plants begin to use these tools, which have 320-volt motors, considered too high voltage for hand-held tools.
*Rockwell offers the Pro-Spec plant-wide torque monitor and control system. GM buys these multi-million dollar installations to control and collect torque data for all critical assembly operations
1985: Stanley introduces a pneumatic assembly tool with torque transducer, angle encoder and integral solenoid valve. This tool allows a new level of torque control by using closed-loop control to measure dynamic torque and shut off the tool when target torque is reached.
Late 1980s: Pneumatic assembly tools with torque transducers and angle encoders are introduced.
1988: Beta Tech introduces the FSC, a low cost single spindle pneumatic tool controller to control any brand tool. GM buys these for point-of-use control systems for pneumatic tools.1988: GSE buys Techmotive Tools and introduces a 160-volt DC electric portable assembly tool line. With this transaction, the vendor becomes a competitor. All assembly tool manufacturers immediately look for other sources for their torque transducers.
1990: Atlas Copco introduces the LTV line of clutch shut-off portable assembly tools. The line is certified into Ford's power tool manual.
*BetaTech introduces CFP (Common Fastener Platform) controller line for DC tools. The concept allows any brand DC assembly tool to be controlled by a common controller. Chrysler and GM buy into the concept.
Early 1990s: Power tools became available with an integrated controller that uses an electronic sensor to control torque.
1994: ISO 5393 is revised; a hard joint is now defined as 30 degrees, a soft one 720 degrees or greater. Ford begins to use this as their standard test method for tool certification.
1996: Stanley buys BetaTech.
1998: Atlas Copco introduces the DS series, a low-cost DC system that eliminates the torque transducer by sensing motor current instead. The series sets a price point for portable DC electric assembly tools.
2001: Stanley introduces the QPS series. A torque controller is integrated into the tool, and torque is controlled with an electronic sensor.
Future Trends…
Cordless Tools.Operators will trade off almost any other tool property in order to be free of the cord. Cordless tools allow more flexible assembly.
Battery Technology.Today's tools use Ni-cad batteries. Developments with nickel-metal hydride, lithium ion and lithium polymer film technologies will lead to higher energy storage and lighter weight. Lithium polymer has the potential to store four times the energy per pound compared to nickel-cadmium.
Fuel Cells. Eventually, fuel cells, probably using liquid methanol fuel, will displace batteries. Much higher energy is possible with liquid fuel.
Wireless Error Proofing. Cordless tools will benefit from RF-based error-proofing systems, which will enable the tool-when the work is in station-to count good cycles and to automatically set the control target depending on the product.
Wireless Networking. Plant-wide data collection will be much easier to install with wireless data communication.
Flexible Assembly for Multi-Fastener Assemblies. Assembly plants need to be able to handle a wide variety of product mix and quick changeover to the next model. Programmable assembly, which uses a single spindle to move sequentially to multiple fasteners, will allow flexible assembly.
Fastener Recognition. Sensing the position of an assembly tool in 3D space will allow operator placement of the tool in any sequence, while the system will recognize which fastener it is about to assemble and set its control parameters accordingly.
Ultrasonic Fastening Control. The ability to measure the actual clamp load of the fastener, rather than measuring the torque, has the potential to completely change the industry. Perfect torque control gives only +/- 25 percent control of fastener clamp load. Ultrasonic control has the potential to deliver +/- 5 percent clamp load control.
