Solution Summary: Tool-balancing Arms
A tool-balancing arm, or zero-gravity arm, is an innovative solution that can hold heavy construction power tools while allowing workers to perform their tasks normally, significantly reducing fatigue and stress placed on upper extremities, and improving the workers’ accuracy and efficiency. More specifically, this tool is designed to increase the safety and productivity of workers who are working on mounted platforms such as scaffolds and lifts.
Several construction tasks (e.g., drilling, sanding, bolting) could involve working on aerial platforms and using powertools (e.g., grinders, impact drills, and chipping hammers) at the same time. Zero-gravity arm systems enable workers to operate these heavy tools comfortably for long time periods. The zero-gravity system can be attached via two spring-arms to scaffolds and aerial lifts to counterbalance the weight of power tools.
The system includes a double-arm unit and universal attachment accessories that ensure secure connection of the tool to aerial platforms (see Figure 1). The zero-gravity arm unit is made of aerospace-grade aluminum and steel, weighs around 35 lb., and can hold tools weighing up to 36 lb. Figure 2 displays the components of the tool: the gimbal emulates the function of hand and wrist; the unique spring and cam architecture of the zero-gravity arm enables uniform lifts throughout a range of vertical heights; and the mounting block helps transfer the payload to the platform.
Figure 2. Top‒three main components of the solution. Bottom‒more details of a zero-gravity arm (Photo courtesy of Ekso Bionics)
Installation of this solution on aerial platforms follows these steps (the accessories are designed and engineered to support a broad range of platform configurations):
• Put the mount on the inside of the aerial basket by positioning the mounting hooks on the top and middle rails and locking them as shown in Figure 3-a.
• Remove the lock pin, insert the arm into the mount, and replace the lock pin as depicted in Figure 3-b.
• Secure the arm by locking the docking ring to the safety latch, then inserting the tool holder into the receiver (Figure 3-c).
Figure 3. Setting up the zero-gravity arm on an aerial basket. a) Set up and secure the mount. b) Set up the arm. c) Set up the tool holder. (Photo courtesy of Ekso Bionics)
After setting up the tool, there are three different ways to attach a power tool to the zero-gravity arm. Figure 4 shows these options.
Figure 4. Tool holders. a) Gimbal. b) Universal. c) Slings and pigtail tool holders. (Photo courtesy of Ekso Bionics)
The gimbal technology (Figure 4-a) gives the worker better control over the tool because it allows the tool to rotate freely (although use of the gimbal is limited to specific tools). The slings and pigtail tool holder (Figure 4-c) provides more flexibility and allows workers to take the tool under the platform and comfortably perform tasks such as drilling the floor. The manufacturer claims that the training time to achieve competency with this tool is only 30 minutes. Zero-gravity arms also are very low maintenance and do not require electricity or compressed air to operate.
Any injuries to the soft tissues (muscles, tendons, ligaments, joints, and cartilage) and nervous system could be classified as musculoskeletal disorders or MSDs (OSHA, 2000). These injuries often damage upper limbs/extremities (i.e., arms, from fingers to shoulder, and neck), lower limbs/extremities (i.e., legs from hips to toes) and back (http://www.hse.gov.uk/msd/index.htm) and can cause numbness, stiff joints, muscle loss, etc. Ignoring ergonomics principles can expose workers to physical stress, including excessive force, vibration, awkward postures, static postures, and repetitive motions that could lead to serious MSDs such as carpal tunnel syndrome (CTS).
The Bureau of Labor Statistics has reported that in 2015 MSDs accounted for 31 percent of all cases of nonfatal occupational injuries and illnesses requiring days away from work. (https://www.bls.gov/news.release/osh2.nr0.htm). Data from National Safety Council (NSC) also show that MSDs are twice as likely to occur in workers’ compensation claims as the total number of claims for amputations, fractures, bruises, contusions, cuts, lacerations, burns, and chemical burns. The National Institute for Occupational Safety and Health (NIOSH) has named construction tradespeople/construction industry among the highest-risk workers/industries for MSDs.
While various risk factors could contribute to MSDs, this study has focused on two conditions: 1) exerting excessive force and 2) maintaining static postures. These conditions can put pressure on workers’ nerves and hurt their tendons.
Many common construction tasks, such as drilling and bolting on aerial lifts, involve repetitive lifting and holding of heavy powered hand tools for extended times in static postures anywhere within the reach of a worker’s arms, from low to overhead, exposing the worker to the risk factors of MSDs. Holding the tool in a stable situation, especially in overhead or near-full arm extension positions, would localize the stresses to fingers, wrists, and arms. In a study on hand injuries, Armstrong and Chaffin (1979) found that forceful exertion with flexed wrist is significantly associated with CTS. Hymovich and Lindholm (1966) also pointed out that grasping hand tools while performing repetitive tasks could cause MSDs to hands. Zero-gravity arms can reduce stressful hand and wrist activity and fatigue by removing the tools’ weight from a worker’s body, shifting focus to the task and not the burden of these heavy tools. This solution also allows workers to securely mount power tools to the arm, minimizing the risk of dropping tools and avoiding struck by injuries.
How Risks are Reduced:
Ergonomic tools are designed to fit a worker’s body to reduce physical stress and eliminate serious MSDs. Evolving from Steadicam technology, spring-loaded zero-gravity arms are types of weight balancers that can alleviate physical stress to workers’ hands and arms. They mainly eliminate the need to use muscular energy to hold construction power tools, especially on aerial lifts and scaffolds; workers can maneuver tools as if the tools were weightless through a patented spring system technology.
A report by United States Ergonomics (http://www.equipoisllc.com/documents/Equipois_zeroG_executive_summary.pdf#view=Fit) indicated that total muscle work could be decreased by 33% when using zero-gravity technology, resulting in a low potential for fatigue. In fact, the results demonstrated that this solution can keep the exertion level below the fatigue threshold. The spring system simulates weightlessness by creating a counterbalance: “each arm uses a large spring that pulls upward with constant force on a tool. When the arm holding the tool moves, the position of the end of the spring changes to compensate for the movement. That's 20 pounds of lift on a 20-pound tool, no matter where it's positioned.” (http://money.cnn.com/2011/03/22/technology/equipois_zeroG/index.htm).
Armstrong, T. J., & Chaffin, D. B. (1979). Carpal tunnel syndrome and selected personal attributes. Journal of occupational medicine.: official publication of the Industrial Medical Association, 21(7), 481-486.
Hymovich, L., & Lindholm, M. (1966). Hand, wrist, and forearm injuries: the result of repetitive motions. Journal of Occupational and Environmental Medicine, 8(11), 573-577.
Occupational Safety and Health Administration. (2000). Ergonomics: The study of work. US Department of Labor.
Effects on Productivity:
One of the main advantages of adopting this technology on construction sites, other than enhancing safety, is the improvement of productivity. This improvement could be achieved by reducing the cost of overexertion injuries; requiring fewer workers’ breaks and rotations due to less fatigue; using more powerful (although heavier) tools; allowing workers to focus on the work; and reducing mistakes. Field tests have shown that using zero-gravity arms can keep workers’ heart rates in a lower range, resulting in much less fatigue and much faster performance.
In a return-on-investment (ROI) study (https://2t2ine2n47g337am722tf6ek-wpengine.netdna-ssl.com/wp-content/uploads/2017/05/Ekso-Bionics-Corporate-Presentation-2017.pdf), the manufacturer claimed that a specific task requiring 3,024 work hours could be done in 1,296 hours when using eighteen zero-gravity arms. Based on a labor cost of $40, and a rent price of $300 per week for each tool, this study reported a $63,720 decrease in cost associated with rental of zero-gravity solutions. Considering the purchase option (with a list price of $11,000), the report concluded that a savings of 45 days of a worker’s time could pay for the price of the tool.
In another case in Hong Kong, IOT network news reported that for drilling work, the zero-gravity system improved productivity by over 50%. (https://www.iot-nn.com/2017/04/25/innovative-zero-gravity-arms-recognised-by-construction-company/). Women and older workers in the construction industry also could benefit from zero-gravity arms and similar tools, which could help create a more equitable workplace in the industry and increase diversity.
• Similar ideas have been adopted in other industries such as manufacturing, aerospace, and defense.
• The training time is short: less than 30 minutes.
• The system requires zero external power and needs minimal maintenance (regular cleaning and occasional lubrication).
• More focus on work and less fatigue could arguably result in fewer mistakes and higher work quality.
• The system is compatible with a wide range of tools.
• The system provides much more flexibility in maneuvering the tools compared to conventional tool balancers.
• It’s also easier to mount zero-gravity arms than tool balancers in construction sites (they usually need large infrastructures).
• The only advantage of tool balancers (which is more apparent in manufacturing than in construction) is their higher load capacity.
Jean Christophe Le, MPH - CPWR The Center for Construction Research and Training
Behzad Esmaeili, PhD - Geroge Mason University
Pouya Gholizadeh - Geroge Mason University
Bruce Lippy, PhD - CPWR The Center for Construction Research and Training
David Chan, CIH, CSP