Sandvik Saws and Tools
Some designers and manufacturers use the term ergonomics to imply quality. A nicely packaged tape measure or air-powered drill is labeled ergonomic, even though it does nothing to remedy repetitive motion injuries. Cushioned grips on the drill might commonly be perceived as an ergonomic feature, even though the designers cite no research to document how, or even if, the padding truly protects the hand.
Imitation ergonomic hand tools can even be counterproductive. For example, common acetate screwdriver handles with their sharp ridges and deep grooves said to “improve the users’ grip” actually do so by biting into the skin on the palm. Eventually, working with the screwdriver causes pain, making workers apply less torque, not more.
Ergonomics has become an overused term, an industry buzzword, so buyers of industrial hand tools must be careful to distinguish between tools that look good and those that truly protect workers while enhancing productivity. Mistakes can be painful and expensive: one case of carpal tunnel syndrome can cost an employer $30,000 in compensation claims and lost productivity. Engineers and designers also need to apply sound research and development techniques to the ergonomic aspects of products they develop before they let the Marketing department slap the phrase “ergonomically designed” on them.
Used correctly, ergonomics have led to advances in worker comfort, safety, and productivity. Recent developments include:
• Adjustable springs in cutters and pliers for electronic assembly to minimize resistance in the handles at the moment wires are cut.
• Antifriction coatings on handsaws let workers cut wood with up to 77% less force than needed using uncoated saws.
• Gradual, V-shaped handle transitions on screwdrivers, rather than abrupt, shaft-to-handle attachments, let workers do coarse and intricate work using their entire hands or just fingertips.
• Thick, wide handles on adjustable wrenches let users painlessly apply two or three times the torque compared to conventional wrenches. The wrenches’ wide handles are also covered with a soft material to help distribute loads over a broader skin area.
While any tool can carry an ergonomic label, those described above are products of a documented 11-point design process. Genuinely ergonomic tools must be validated by such a protocol to quantify actual improvements and the real differences they make to users. In short, ergonomic tools must be proven to reduce risk of both direct and long-term injuries, and to make the job easier.
At the very least, ergonomic hand tools should reduce the risk of direct injuries, such as cuts and bruises. This is why ergonomic tools have rounded contact areas and protective shields to prevent cuts. Properly designed pliers, for example, have no unnecessary sharp edges, even around the jaws. Flared guards on file handles keep fingers from slipping forward over sharp blade tangs much like the guards found on good cutlery.
Ergonomic tools should also minimize the cumulative wear and tear on skin that leads to abrasions, blisters, and calluses. The handles of the ergonomic screwdrivers have a hard core surrounded by a soft thermoplastic gripping surface to protect the skin and preserve the grip. The improved traction between hand and handle prevents rubbing.
Safe design should also ensure that tools will not pinch or snag hands between closing parts. Ergonomic slip-joint pliers, for example, have handles that remain open when the jaws are fully shut to keep from pinching palms.
All these design features address the obvious risk of direct surface injuries. The more complex design challenge is to prevent long-term injuries caused by repetitive motion.
Cumulative trauma disorders, (CTDs) are repetitive motion injuries. The force, precision, and degree of repetition a specific task requires determines its risk of causing a CTD. Most CTDs occur in the hands, which have around 17,000 pressure-sensitive nerve endings and are filled with arteries, veins, and capillaries. Repeated hard blows and sustained pressure on almost any spot can compress nerves and rupture blood vessels, causing numbness, pain and swelling. Over time, high loads on muscles and tendons cause sprains and epicondylitis — the painful tennis elbow sometimes felt through the forearm. Meanwhile, bones and joints routinely subjected to heavy shocks and stresses deform or become inflamed. Workers eventually fall victim to bursitis and other neuromuscular diseases.
Such long-term injuries are the result of several risk factors. Debilitating carpal tunnel syndrome, for example, is caused primarily by poor work positioning or awkward wrist posture. However, the risk of carpal tunnel and other nerve injuries is compounded by high loads.
Ergonomic tools should reduce the effort and musculoskeletal stress required to perform repetitive tasks, thereby protecting workers from long-term injury. Ergonomic design addresses several related risk factors and injury mechanisms.
To reduce the risk of long-term injuries, ergonomic tools are optimally weighted and balanced for their function. Tree cutters designed for professionals who cut thousands of branches a day, for example, have lightweight handles. The handles are carefully balanced to make the cutters more comfortable to use, especially at chest height or overhead.
Large gripping surfaces spread loads evenly and reduce the chances that long-term pressure will restrict circulation and deform or damage joints. For example, pliers with broad grips distribute and reduce hand pressure while screwdrivers with rounded handles prevent pressure points no matter how the tool is held.
True ergonomic tools also deliver the greatest power with the least effort. Low-friction handsaws maintain smooth cutting strokes with low resistance, whereas uncoated blades bind and jerk, adding impact forces to already high friction loads. Wire cutters from Sandvik Saws and Tools Co. have self-adjusting springs that reduce their resistance as the cutter’s handle are squeezed closed, exerting minimal resistance when the wire is cut.
In addition to preventing injury, ergonomic tools should make the job easier. Screwdrivers with color-coded caps, for example, help users locate the right driver quickly. And low-friction saws use handles with an index-finger groove for better control.
But not all tools with such features have validated ergonomic designs. It pays to look beyond ergonomic labels and carefully evaluate the claims of manufacturers, and ask for the supporting research.
Getting the ergonomics right
At Sandvik, engineers apply an 11-point process that ensures the tools they design will be ergonomic and have real benefits. The two-to-three-year process relies on user research to validate a design and begins with a preliminary specification covering the function and working environment of the tool. Background research identifies common injuries and risk factors.
Professional users test prototypes and results are quantified by electromyography to gauge muscle tension and a goniometer to track users’ hands. Prototypes are revised and tested again by more users to improve function and comfort. Pilot production tools are evaluated once more before the tool goes on the market. A five-year follow-up verifies that the ergonomically designed tool is being used properly to prevent injuries. With multiple iterations of testing and refinement, the 11-point process is neither simple nor cheap.
The recent, successful development of a wire cutter provides a good example of Sandvik’s design process. The cutters are part of Sandvik’s Rx Series for electronic assembly. Electronic assembly work is a repetitive precision task with a high risk of strain injuries. Workers can make up to 10,000 cuts/day and up to 120 cuts/min. Although carpal tunnel syndrome is tied to the position of the hands and the work, the magnitude and distribution of hand loads are contributors. Sandvik engineers set out to design a cutter that would be used by a mostly female work force with relatively small hands and alleviate stresses on the palm.
More than a half-dozen different prototypes were developed to evaluate different handle configurations that would reduce loads on the palm. Long, straight handles didn’t conform to the curve of the hand, and cutters with one curved handle and one straight actually increased the chance of injuries when a left-handed worker used an irreversible right-handed tool. Hourglass handles fit the hands of only part of the user population. Heavily cushioned handles denied users operator feedback. Prototype research finally provided the most comfortable and efficient solution: wide, slightly rounded, and extra long handles. Wide, round handles distribute forces over a wider area than conventional grips. The extra length let them extend beyond the sensitive median nerve area in the palm to dissipate damaging hand loads.
As a person squeezes a conventional pair of spring-loaded pliers, resistance increases as the tool closes. Then, when spring resistance is at its maximum, it combines with the force needed to actually cut the wire. To minimize the peak force for each cut, the Rx Series cutters used an innovative spring dubbed the Biospring. It opens the handles automatically, but reduces the force required to close them as a user squeezes. By the time the jaws close, the only force on the handles is that required to actually cut the wire. To fit different hands, the spring adjusts, letting user set how wide the handles open.
Carefully documented user feedback provides important data for the design process. A five-month scientific survey verified that users preferred the comfort of the ergonomic tool over the previously used clippers.
Industry is already aware of the importance of ergonomics, but it must also understand the real value of genuine ergonomic hand tools. As workplaces become safer from hazardous materials and disabling accidents, repetitive motion injuries will become a larger portion of all injury claims. Higher productivity and fewer injuries can counter the higher cost of ergonomic design and tools.
11-Point Program for Ergonomic Tool Development
1. Define the tool being developed with preliminary specifications.
2. Conduct market analysis to determine which tools professional users prefer.
4. Build working prototypes. To focus users on product performance, prototypes are made from the same material and in the same colors.
5. Record first prototype handtools at work (User Test #1).
6. Evaluate and modify prototypes.
7. Survey a wider selection of users (User Test #2).
8. Produce a production-representative prototype based on final design recommendations.
9. Generate manufacturing specifications.
10. Prepare for tool launch by production (User Test #3).
11. Five year follow-up gages user reactions in the field.
Show Me the Research
• Compare designs. Look for ergonomic features that address CTD and other risk factors in your application.