Proper workplace and connector design reduces worker stress and boosts product reliability
By David Erickson, field application engineer with the appliances business unit of TE Connectivity
Connector assembly is a critical function in appliance manufacturing. Many connectors are used in power and controls circuits of washers, driers, refrigerators, ovens, and air-conditioning systems. In recent years, the task of connector assembly has become more complex. That’s because advanced sensors, controls, and communication/networking capabilities being used to make more intelligent appliances also require more connectors of many different types. Although robots and automation can be used for some connector-assembly tasks, many connectors are still assembled by hand. Proactively identifying ergonomic issues that affect a worker’s performance helps reduce human error, but also improves workplace efficiency and safety. By focusing on ergonomics — the science for optimizing the design and arrangement of the work environment — manufacturers can spot problem areas, implement best practices, and select appropriate connector designs. The goal is to reduce human error in the factory and product repairs in the field.
Focusing on the ergonomics of connector assembly
Workers tend to make mistakes when they perform hours of repetitive motions during the assembly process of mating two connectors. These repetitive motions may cause carpal tunnel syndrome (CTS), strained muscles and other physical injuries that impact workers’ productivity, morale and health.
Key challenges that arise when connectors are assembled in the manufacturing workspace include:
- inappropriately arranged workspaces that cause repetitive strain injuries;
- connectors that are improperly mated resulting in production line and field failures;
- high mating force required for some connectors resulting in injury to production line workers, connectors not being fully mated, and latches not being fully engaged.
Production line failures and high employee turnover directly impacts a company’s bottom line and interrupt the flow of the manufacturing floor. Field failures can strain your sales managers’ relationships with their customers brand reputation and, indirectly, decrease future revenue.
Prevention is key to addressing these challenges and can be approached by focusing on using ergonomically friendly connector designs and creating a more ergonomic workspace.
Creating a more ergonomic workspace
Today’s manufacturers are challenged to address the repetitive motion and forceful exertion of manual assembly efforts. This is where ergonomics can play a critical role.
By adapting tasks, work stations, and equipment to fit workers, ergonomics seeks to reduce physical stress on a worker’s body and minimize or eliminate serious work-related musculoskeletal disorders (MSDs). A specific methodology should be employed to adjust the workplace to meet employees’ ergonomic needs, which could include these steps:
Step 1: Evaluate the operator’s tasks and risk factors.
Understanding and documenting the sequence of tasks performed by an operator can identify associated ergonomic risks. For example, a connector assembler needs to exert force using his wrist and fingers to press the female and male connectors together. The repetitive movements of gathering and locking the connectors may cause CTS.
Step 2: Use workspace redesign, process/tool improvement, policy change and personal accessories to mitigate risks.
Evaluate each task and assign its associated risks and remedies to four relevant categories: workspace redesign, process/tool improvement, policy changes and personal accessories (Figure 3).
Appropriate remedies should be documented and communicated clearly. Behavioral changes should be reinforced through frequent training and education. Creating a training and communication plan help ensure workers are educated on ways to reduce risk of strain or injury.
Step 3: Evaluate your workspace by using workspace design principles.
For every task, workspace setup is crucial. It is important to consider a range of elements when designing a workspace.
For workspace design, understanding “primary reach zones” is critical to ensure that work is handled most efficiently. These zones are vertical and horizontal areas that a worker can reach with minimal arm, head, or trunk movement. The ideal ergonomic solution is to keep all connectors within the primary reach zone. Additionally, to minimize stress for seated employees, the workstation height should be adjusted to support the particular task.
Ergonomically friendly connectors
Designing connectors is both an art and a science. Connector design engineers need to design for mechanical and electronic needs, reliability requirements and space constraints. They also need to consider human factors by providing intuitive and subtle “reminders” to ensure connectors are connected properly.
Many common problems occur when workers spend hours assembling connectors. Some trouble spots are obvious; others are easy to overlook. Key issues that arise when connectors are assembled in the manufacturing workspace involve:
Production Line Workers
Issues: The pounds of force that a connector requires to be properly mated greatly affect worker stress and productivity. When lower pound-force can be used to create a normal contact, the worker’s task may become easier. Insertion force is a factor of the coefficient of friction, resistance to abrasion and other mechanical variables. Connector design and materials play a key role in reducing friction. For example, a tin-plated brass receptacle terminal designed for low insertion force (LIF) requires 6 lb (27 N) of force on average, which is 40% to 60% lower than the 10 to 15 lb of force required for non-LIF designs. In the case of point-to-point power connectors, LIF designs need a maximum mating force of only 1.5 lb per contact. Of course, when 10 to 12 contacts are involved, the forces add up to 18 lb of force or more for connector mating. High peak insertion forces raise a number of problems — such as CTS — which are addressed by recent connector design solutions.
Solutions: Today’s appliance manufacturers can employ advanced connector designs that improve on standard connectors that have not changed in decades. When encountering higher connector counts due to more signal and power lines in more complex appliances, workers can benefit from LIF terminals and or connectors and terminals. In many situations, it’s worthwhile investigating the benefit that LIF connectors designs bring compared to applying a lubricant to the terminal to reduce mating forces.
Newer designs offer benefits that may include:
- employing adequate and safe push points for leverage during the connector-mating process;
- giving an audible “click” and tactile feedback when the connector is engaged so production workers know when to stop applying force;
- providing a visual key to avoid jamming connectors together in the wrong orientation, such as rounded edges on housings and lead in of connectors to further reduce assembly issues.
Issues: Appliance manufacturers often use subcontractors to fabricate harnesses that assemble cables or wiring into bundles. The ends of wires are pre-fitted with the required terminals or connector housings to save installation time. The subcontractor is responsible for properly crimping the individual terminals and inserting them into a housing. Several ergonomic issues may be encountered, such as repetitive strain injuries and back-outs for terminals that are not fully seated in the connector housing.
Solutions: In some cases, automated harness assembly tools can be used to handle harness-making issues. However, manufacturers who must rely on manual operations benefit from optimizing the workspace by:
- consulting with the connector supplier to create a board system with materials and accessories arranged in a convenient, ergonomic layout;
- simplifying and reducing the number of crimps where feasible;
- avoiding sharp edges that can cause wire snags and using connectors with protective ribs to prevent wire entanglement and latch breakage;
- using correct tooling.
Issues: Maximizing the reliability of each connection requires proper contact seating, contact retention, and position. Otherwise, contacts and or connectors may become loosened during shipment or vibration in operation. Connector reliability problems are often the result of worker errors, which may include inserting contacts improperly in housings.
Solutions: Selecting connector designs that help prevent worker errors can reduce rework in the factory and repair work in the field. Beneficial connector features include:
- offering connector and terminal polarization so workers can perform mating and assembly in only one orientation;
- offering keying options and multiple connector color options in situations where mating multiple connectors of the same position size may create confusion;
- providing an audible and tactile feel that lets assemblers know the connector halves have been fully mated; and/or
- using a terminal position assurance (TPA) device to improve alignment of the terminal in the connector housing, which results in less chance of terminal stubbing as well as reducing mating forces.
Best practices based on experience
An experienced connector supplier can not only boost connector performance, but also human potential. The supplier can offer worker training that complies with the Wiring Harness Manufacturers Association (WHMA) IPC/WHMA-A-620 standard. They can also offer insights into best practices that can help minimize human errors while improving workplace ergonomics.
Figure 5: Anatomy of a 15-position connector design employing polarization, terminal position assurance (TPA) and flat tab and receptacle contact design for low mating forces (courtesy TE Connectivity)