Reductions in effort and improvements in comfort lead directly to increased productivity. Because an ergonomically designed tool is more comfortable to use, it will accomplish the same work with less effort than a conventional tool. Less effort means less likelihood of worker injury.
A wide variety of assembly products, such as power tools, hand tools, dispensers, workstations and chairs, offer ergonomic features. Indeed, many tool suppliers tout their products as "ergonomic." However, caveat emptor applies. It's important to distinguish between cosmetic styling and genuine ergonomics.
Selecting the correct product can reduce the threat of overexertion and repetitive motion strains on the assembly line. Before evaluating any item, look for the following basic attributes and criteria:
- Low torque reaction in power tools.
- Low impulse vibration in power tools.
- Neutral hand and wrist positions.
- Low muscle effort.
- Adjustability and flexibility in workstations and chairs.
- Low peak pressures across the grip with a generally even pressure distribution.
- Trigger pressures below 22 psi on power tools.
- Correct tool balance for the application.
Power ToolsErgonomic attributes of power tools include good grip, along with low weight, vibration and torque reaction. Anything that interfaces with the operator, such as the housing, noise level and handle, must be considered.
Simple design features can make a big difference in reducing operator effort. For example, bending the hand down 65 degrees results in a 55 percent loss of available grip strength. The optimum position for transmitting forces between the hand and arm is to ensure the wrist is kept straight and is not twisted. Many tool suppliers have taken this to heart.
The first contact an operator has with a power tool is its handle. It determines how well the assembler can grip the tool without wrist twisting or hand slippage. This interface, along with tool weight, will affect whether or not an operator can maintain his hand in a neutral position.
Housings also play an important role. "In an assembly environment where you have repetitive motion, the operator will sweat, which makes holding and using a tool with an aluminum or steel housing very uncomfortable," says Lori Logan, marketing manager at Deprag Inc. (Lewisville, TX). Logan's company uses a plastic composite on its tools to absorb perspiration and oil.
The shape of the housing is another ergonomic design feature to consider when evaluating screwdrivers, nutrunners and other devices. "Tool manufacturers often force the operator to hold a round tool when his grip is not round," Logan points out. "A round tool requires the operator to grip harder to apply the same torque as our tool." Its ovoid shape positions the index finger tip toward the thumb. The tool also has four distinct corners where the two fingers come together for a design that provides a comfortable, slip-free grip. Since the operator needs to apply less force to firmly hold the tool, he can work longer periods without fatigue.
"The housing widens toward the bottom of the tool, so that the grip is larger where the little finger rests," says Logan. "This design enables the operator to easily grip the tool without slippage, which is important since most of these tools use a push action to start the tool."
A high friction surface on the handle can also improve gripping and allow ventilation, says Bo Lindqvist, an ergonomist at Atlas Copco Tools & Assembly (Farmington Hills, MI). His company's line of power tools feature a tapered straight handle to allow all fingers to grip equally. The design locates handle-to-hand contact angles in strategic locations. "The pressure-contact area of the handle should be at the fat pads of the hand, since fingers and palms cannot withstand excessive pressure," Lindqvist points out.
The use of pistol handles can shorten a tool's length and reduce the bending load on the wrist. Regardless of hand size, the angle on the pistol handle should be around 70 degrees, which corresponds to the natural angle of the hand grip. "This angle makes the tool feel like an extension of the operator's hand," says Logan.
Tool manufacturers have invested a large amount of time and money in ergonomics research in recent years. "Over the last four or five years, we have taken a holistic approach to design products for the user and the application," says Bill Dwyre, worldwide director of marketing at Ingersoll-Rand Co. (Annandale, NJ). "We spent a lot of time on the hand-interface shape, paying attention to the center of gravity of the tool, locating it in the center of the hand so the tool doesn't feel back- or front-heavy."
After extensive testing, Dwyre's company settled on an egg-shaped cross-sectional design of its straight tool handles and a textured grip. The tool handles also feature a flare or flange to prevent hand slippage on the tool.
To adapt the tool to the hand size of the operator, Ingersoll-Rand's pistol tools feature an interchangeable grip. Adjustable handle sizes are built into its line of air- and electric-powered angle nutrunners. "There is no need to add any parts to change the handle from a small to a larger size," claims Dwyre. To change the handle size, the user slides a tube on the end of the tool back, then up onto a track to create three different tool-handle diameters.
During shut off, power tools typically experience a kick or torque reaction generated by the clutch, which can cause many different types of hand and wrist injuries. A variety of clutch designs, as well as handle designs, attempt to reduce the amount of torque reaction the operator feels.
"The clutch is an important issue on repetitive assembly work," explains Logan. "We designed our screwdrivers with a special clutch that reduces the impact at shut off." This soft-touch clutch design delivers a softer click at shutoff relative to conventional clutches, which translates into less strain on hands, wrists and elbows. This soft shut off also means greater product quality, especially on sensitive assemblies. "Sometimes, the impact of the shutoff transfers from the motor to the bit then to the product, which can potentially cause damage," notes Logan.
Right-angle tools are second to straight tools in presenting low or no rotational force to the operator's hand. "Most of these are lever tools," says Logan. "As torque travels from the clutch, it meets the angle, which prevents the torque from traveling past the lever."
Another means of combating torque reaction is through torque arms that support the weight of the tool and absorb torque reaction. These devices make tools more ergonomic as they get into higher torque levels.
"The heaviest parts of a power tool are the motor, gearing and clutch," says Logan. While these may not present a balancing problem with straight screwdrivers, these items can make pistol-grip power tools nose-heavy.
"Horizontal assemblies, where you would use a pistol grip, require a well-balanced tool," says Logan. To make pistol tools lighter, Deprag employs a short nose design. "This also keeps the operator's hand from having to extend downward."
"Most of the larger tool companies have made major advances in making more ergonomic tools by addressing torque and operator comfort, but there are certain laws of physics you just can't get around with a handheld tool," says Bob Reid, vice president of Weber Screwdriving Systems Inc. (Mount Kisco, NY). To remove any interface, Weber and other companies supply assembly systems with mounted tools. "We ask people to consider taking the tool out of the operator's hands, which removes issues of tool weight, vibration and torque," explains Reid.
More and more manufacturers are also using lightweight materials for their tool housings. According to Dwyre, "The benefits of composites in air tools are several-fold. First, of all they reduce weight."
The composite construction also provides insulation from the cold conducted through the handle from the air. "We take the composites construction further by adding glass-filled nylon to create a structural composite," says Dwyre. "We then overlay that with a soft-touch material with a rubbery feel that allows the user to grip the tool with less force."
Designing and building tools with high power-to-weight ratios is another way to reduce tool weight. "Heavy tools not only put a higher load on the wrist, they also make precision tasks more difficult," says Lindqvist.
AIMCO (Portland, OR) claims the titanium and magnesium parts used in its nutrunners make the tools 20 to 40 percent lighter than comparably sized models. According to Norma Lauzon, an AIMCO spokesperson, "lighter weight tools not only contribute to a high level of operator comfort, they also reduce fatigue, increase productivity and contribute to overall work quality." The tools feature a high power-to-weight ratio. "The higher the [ratio], the higher the torque and speed, and the lower the weight of the tool," says Lauzon.
Hand ToolsHandle angle, grip and weight are just as important in hand tools as they are in power tools. The amount of force the worker applies when using pliers, snippers and other tools is another ergonomics issue. This comes into play in the design of the handle, head and cutting-edge.
Unfortunately, the market has been flooded with cheap tools with fancy-looking handles that purport to be ergonomic. "A comfortable handle alone will not bring the desired ergonomic benefit, particularly if it will not cut or grip properly," warns John Hopkinson, manager of industrial sales at Anglo American Enterprises Corp. (Somerdale, NJ). "Genuine ergonomics in hand tool design seeks to reduce the amount of feed-force or hand force necessary to achieve a given task, such as cutting, gripping, turning or driving a screw."
Tool design starts by understanding how the human body works. "An understanding of how a tool will be used and the mechanics of the human body allows us to create a better ergonomic tool," says Gary vanDeursen, corporate vice president of innovation and design at Stanley-Proto Industrial Tools (Covington, GA).
"The ideal design fits how the hand and body work. The hand can rotate through one-third of a circle. Beyond that point, the worker is flexing his arm too much."
Tool handles from Stanley-Proto feature a soft rubber cover. "With some rubber, it can be too soft or too hard," explains vanDeursen. "This one is just right. It also features a small diamond pattern we have tested extensively. The texture provides a number of edges that are close together, which makes for better force application."
"The handle of the tool should be as comfortable as possible and spread the load over a broad area to avoid localized pressure points on the palm and fingers," adds Hopkinson. A contoured and grooved handle improves the gripping ability of the operator's hand, as does two-component handles with soft and hard surfaces. The latter also maximizes comfort.
Anglo American's line of hand tools feature a curved-angle contour that provides a wide, rounded contact area. "We use lightweight materials, such as chrome-vanadium steel, to reduce weight without losing strength," explains Hopkinson.
Aven Tools Inc. (Ann Arbor, MI), a supplier of ergonomically designed hand tools and soldering stations, considers the same features in its hand tool designs. "We have scientifically designed our cutters and tools so the handles fit the hand better," says Mike Shahpurwala, Aven's president. "They provide a large surface area to present fewer pressure points on the hand."
Fewer pressure points mean the operator will not feel any pain or discomfort when working long hours. To make screwdriver handles still more comfortable, Aven enhances the handle design by constructing the handle from a soft material. The material allows workers to apply greater force to the tool and, thus, higher torque. It also absorbs perspiration to eliminate tool slippage.
Xuron Corp. (Saco, ME) also designs its tool with a comfortable grip and handles that don't generate pressure points. "We make the handle shape to fit the hand with the handles extending beyond the palm to avoid the handle ends from cutting into the hand," says Mark Hamilton, Xuron's sales manager.
Return springs on pliers and cutters save the operator from repeatedly opening the tool. For someone doing a heavy amount of cutting, such as plastic trimming and deflashing applications, this characteristic can be important. "If there is too much tension in the spring, the operator has to counter when closing the tool, and that can lead to fatigue," Hamilton points out. "We build in a light spring action that will open the tool but still allow easy closing."
To accommodate different-sized hands, many hand tools come with different handle lengths. For instance, Xuron offers a curved handle that allows an assembler to get the head into tight areas without moving his wrist.
DispensersHand applicators and plastic squeeze bottles or tubes that are used to dispense adhesive, solder paste and other materials require assemblers to do more than simply apply the fluid. The operator must also pay attention to the amount applied and its placement. In addition, repetitive hand pressure from squeezing often leads to fatigue.
Automatic dispensers reduce worker fatigue, enabling assemblers to work longer without discomfort. Ergonomic syringes allow operators to hold the devices comfortably; the process is similar to using a pen.
Air-powered models are ideal for repetitive work where joints are uniform in size and shape, and under factory conditions where air lines are available. They are lightweight and require minimum physical effort, which is ergonomically beneficial.
Material is forced from a syringe and out of the dispense tip by a piston when air pressure is applied behind the piston. Lower pressure is used for thin fluids like cyanoacrylates and solvents; higher pressure is used for thick materials like sealants and greases.
"Air-powered dispensers that use a timed air pulse to apply controlled, repeatable amounts of fluid are a highly productive alternative to hand applicators such as squeeze bottles, tubes, swabs and toothpicks," says Claude Bergeron, a fluid application specialist at EFD Inc. (East Providence, RI). "Controlled air pressure, instead of hand or finger pressure as the force used to apply the fluid, reduces repetitive motion and the risk of carpal tunnel syndrome."
"Dispensing is really a multiple task operation," explains Bergeron. "As morning moves into afternoon, the operator's ability to repetitively and consistently perform these tasks diminishes. Quality decreases, as does production output. By removing the variables from the process, air-powered dispensers can help assemblers raise adhesive application from an art to a science."
With air-powered dispensers, the operator needs only to concentrate on tip placement and depressing a foot peddle or finger switch to initiate the dispense cycle. The goal is to make the assembly application easier, simpler and more accurate.
"The worker's attention is no longer divided between placing the tip, applying the adhesive, monitoring air levels and making adjustments to the dispenser," says Jere Donohue, CEO of Intelligent Dispensing Systems Inc. (Encino, CA). "This eliminates overfills and underfills. That translates into lower material costs and less costly rework or the scrapping of some electronic components."
WorkstationsBefore selecting a workstation, it's important to evaluate the assembly application and existing production processes to develop an optimum work environment. "You can spot trouble areas right away," claims Karl Wojcikiewicz, product marketing manager for ergonomic workstations at Bosch Rexroth Corp. (Buchanan, MI). "Foam rubber taped to equipment edges, boxes under workstations to support the worker's feet, and tape put on air tool handles to counter vibration or the cold temperature of the tool. These indicate ergonomic problems and indicate the potential costs that may arise due to injuries."
Wojcikiewicz says there are a number of general guidelines to consider when setting up a work area. "You don't want to bend, twist or stretch at the workstation," he advises. "No work should be above the level of the heart, and you don't want to lift more than 10 pounds with the arm extended."
Working methods, work size, work area layout and training all contribute to a successful ergonomic environment. "One of the first things people need to understand is that the product, by itself, will not perform magic for the company," says Ray Gottsleben, vice president of sales and marketing at Arlink Inc. (Burlington, ON). He believes a workstation must be set up correctly, the task sequence designed correctly, and the worker trained correctly to realize all the benefits of an ergonomic workstation.
"A primary principle in creating an ergonomic work area is to ensure the worker performs his task without a lot of force while holding his body in a nonawkward position," adds Joy Ebben, Ph.D., an ergonomist at IAC Industries (Brea, CA). "This is the first line of defense."
Supervisors need to match the people and the job with the workstation, says Ebben. Much goes into assessing which workstation matches these requirements. Work methods are a key consideration. For instance, are the assemblers working alone or in a group? Is it a progressive assembly or is the complete assembly done at one stand-alone station? What kind of people will be performing the work? Manufacturing engineers also have to consider the types of tools being used and the demands for electricity, air and lighting.
Another important factor is whether the assembler will be standing or sitting. "This can be tough to determine," says Ebben. "Putting plastic tips on wire is a simple, light task easily supported by a bench with four legs and a chair. But, if the part is a 2-foot tall chassis, the assembly operation may require a hydraulic workstand."
Companies operating more than one shift will require workstations that can accommodate a number of different workers during a 24-hour period. Assemblers should be able to optimize their workstations quickly and easily.
Indeed, adjustability is key to making a workstation fit the person and the assembly task. Some suppliers offer aluminum extrusions that make workstations flexible. Special T-slots in the aluminum extrusions allow quick and easy movement of parts bins, work instruction holders, lighting and other accessories. "The T-slot is an ideal method," claims Wojcikiewicz. "This makes the workstation nearly infinitely adjustable for any situation and worker."
Other attributes to consider in a workstation are surface height, angle and depth; the ease of adding or changing shelves and other attachments and accessories; and comfort features such as beveled edges.
It's important to efficiently use the vertical space around the workstation. "Vertical space includes the entire distance from the floor to the upper limit of the workstation," explains Gottsleben. "Tools and parts should be within easy reach and organized around the worker. Any items that are not used as often should be stored up high or even below the work surface."
Product life cycles can also place demands on workstation flexibility. "The life of today's products continues to shrink," notes Duff Elleby, president of Ergosource Inc. (Wayzata, MN). "Manufacturers are challenged with tearing down old lines as a product's life expires. As a result, any capital investment must be flexible. By using modular components, an ergonomic workstation can be disassembled and then reassembled using the same components to create a configuration appropriate to the new process requirements."
"Change is inevitable and constant," adds Gottsleben, "so workstations need to accommodate that fact, and be easily and quickly reconfigured when the need arises."
ChairsSitting is often harder on the back than standing. As a result, chairs should adjust to suit an individual's comfort level.
"Seating is an important operator interface to the workstation," claims Gottsleben. "People who are uncomfortable in their seats will tend to get up and walk around more often. These 'walking wages' are costly and add no value to the bottom line."
Inadequate seating support places unnecessary strain on the back, leg and stomach muscles. According to James Frobose, manager of engineering at BioFit Engineered Products (Waterville, OH), an ergonomic chair supports a balanced work posture and minimizes fatigue. "A balanced work posture means the torso and hips are supported so that minimal force is exerted to hold the torso stable," Frobose points out. A stable torso provides a better anchor for arms, hands and legs, resulting in less fatigue and less risk of cumulative trauma disorders.
A wide variety of seating types and adjustment options is available. "The options are huge," says Ron Buettner, vice president of sales and marketing at Bevco Ergonomic Seating (Waukesha, WI). "They can have tilting backs, height-adjustable backs, seats that slide, tilt and raise or lower, and adjustable arms in width, angle and height." Such adjustments should allow a seat to accommodate a range of different-sized people.
These adjustments also provide assemblers with the means of changing chair positions throughout their shift. "Someone sitting in the same manner all day can become uncomfortable," explains Buettner. "The chair needs to be able to conform to multiple seating positions so it remains comfortable throughout the day."
"You want the ability to raise and lower the seat height in any increment within the range of the pneumatic cylinder," adds Gottsleben. "Chair lifts come in different ranges, depending on whether it is a chair or a stool. Back depth, or the distance between the front edge of the seat and the back support, should also adjust to compensate for the length of a person's upper leg." Another important adjustment is back angle, or tilt for lumbar and back support.
Good circulation should always be maintained. "A seat pan that tips forward a little bit and has a waterfall front edge rather than a square edge improves blood circulation in the legs and eases fatigue," says Gottsleben. Along with the waterfall front edge, chairs should typically be at least 1-inch wider than the hips and thighs on each side. A concave seat contour will evenly distribute an assembler's weight.
Foam used in the construction of the chair is also important, but often overlooked. "Foam is produced with varying characteristics and quality," warns Gottsleben. "Some will break down over time and take a permanent set, at which point it loses its ability to adequately support the person." Better quality foams will continue to spring back and provide consistent support over time, even when the chair is used by a variety of people, molding itself to each individual's particular contours.
Robust chair construction contributes to long-lasting support and adjustability. While inexpensive office chairs may offer low-cost adjustability, they are not always suited to the plant floor. "There is a wide range of chair quality out there with a wide range of features, hence a wide range of costs," explains Gottsleben. "It is important to educate yourself on the differences between them and understand the reasons for pricing differentials.
"Design, and the quality of components, materials and construction techniques used in industrial seating, covers a broad spectrum," adds Gottsleben. "Seating can be subject to a great deal of abuse and wear and tear. It's important to invest a few additional dollars for a quality product that will last."