How to determine the ideal level of torque when specifying hinges

By James Stroud, Commercial Product Manager
Southco, Inc.

One of the most common and widely used devices used today is the door hinge. It is so ubiquitous that it’s often taken for granted. However, industrial and systems designers know that hinge technology offers a range of functionality and design options that can be used to improve even simple operations.

When designing an application that hinges two panels together — whether it’s for simple enclosures or large, complex medical equipment — choosing the appropriate level of torque is essential for reliable operation and an intuitive end-user experience. A proper understanding of the different levels of torque and which applications they are best suited for can help device and systems designers choose the ideal hinge solution.

A closer look at torque
Torque has a relatively simple definition: It is the amount of energy or effort needed to move a door or panel from its closed position to an open position. The energy required depends on the weight of the door and the travel distance or arc of motion from closed to open (and back again). It’s also important to consider function and the need to move the panel to one point in the arc of motion and hold it, or to have the motion go from fully open to completely closed.

Today’s suppliers of hinge and positioning technology have portfolios that supply a “torque continuum,” or a range of hinge products with different torque characteristics. Industrial designers can choose the ideal options to meet functionality, ergonomic requirements, quality, and unique features.

These include:

• Holding doors open or closed, and moving panels securely into position without secondary supports or additional components
• Creating an intuitive, zero-drift motion so that when a door or cover is opened, it holds a user-defined or predefined position securely, and with one motion
• Providing specific tactile feedback to enhance the quality perception of the hinged device
• Eliminating additional components (such as gas struts) or routine maintenance (tightening screws to maintain hinge resistance), thereby helping to lower overall costs
• Providing a smoother, more substantial feel to opening and closing action, or to eliminate vibration The torque profile in a selected hinge can change – or elevate – the user’s perception about a particular device

Consider the airplane tray table. Seating designers must use extremely lightweight plastic components in these applications to help airlines reduce fleet weight and conserve fuel. However, a tray table that flops down upon opening can lead a passenger to question the quality of the aircraft itself.

Using a constant torque hinge with a factory-set level of resistance, the tray can be lowered by the passenger with just the right level of force, making the tray feel more substantial — and creating a positive perception of the inflight environment. Additionally, constant torque hinges designed and manufactured with high-quality materials retain the desired resistance after thousands of flights, without maintenance or replacement of parts.

Choosing the right hinge
The most common hinge is also the simplest: the standard, free-swinging hinge for opening and closing, with no resistance. It requires people to exert all the necessary energy to open or close a panel or uses gravity to complete the same operation.

Beyond this basic device, hinge technology can be broken down into four major categories, or “building blocks,” based on the type of torque and controlled motion they supply.

• Constant torque – enables the device to be held securely at every position along the range of motion
• Detent and bistable – these hinges automatically drive to and hold a specific position, such as to 90 degrees
• Damping – hinges that control the speed of motion automatically, without holding
• Counterbalance – hinges with technology that enables heavier objects to feel lighter when opened, or pop open with a simple touch

Although many applications would require only one type of hinge, these different categories can also be combined into hinges that provide multi-functional positioning options in a single device. There are three key factors to consider when selecting the ideal hinge with the ideal torque profile: weight, center of gravity, and direction of movement.

Weight: If a panel is sufficiently light — under a few pounds, for example — then a simple hinge with no torque can offer the most cost-effective solution. As the weight of the door or panel increases, constant torque or detent hinges become more effective solutions. The level of torque in these hinges requires the user to exert some force, but prevents the door from falling. As a door panel’s weight approaches 15 to 20 lbs, and upwards of 500 lbs, counterbalance technology provides a more effective option. With a counterbalance hinge, the hinge prevents the door from falling and makes that door feel lighter so that extra effort is not required to open or close the door.

Center of gravity: The center of gravity for a door or panel is affected by the width and shape of the panel, as well as the location of additional components that are attached to the panel. A light door that has a center of gravity far from the hinge point might feel the same as a heavier door with a center of gravity close to the hinge point. For example, a tractor hood covering an engine compartment might be narrow and made of lightweight material, but because it’s so long, the center of gravity is farther out and requires more torque to lift it than a box or a panel that’s only 12 or 18 inches deep.

Direction of movement: First, it is important to determine whether the panel or door is hinged vertically or horizontally. If the door is hinged vertically and moves side to side, it is working with gravity. The opposite is true for horizontally hinged panels. In some cases, a horizontally hinged door may also need to be moved and held into place in a vertical position. This way, a technician can access and work on the interior of a machine. The energy needed in this situation to move the door from horizontal to vertical will be greater, so a constant torque or counterbalance hinge might make more sense — and particularly when a technician is working underneath a door that needs to be held open overhead.

A secure hold: Constant torque
Constant torque hinges offer a device intuitive movement, so that the amount of effort to move it is just enough to respond to deliberate motion. However, the device will hold in place for basic touch interactions.

One example of this is a touchscreen monitor at a supermarket’s checkout counter. A constant torque hinge attached to the monitor’s base lets a user tilt the monitor up and down for optimum viewing and interaction. At the same time, tapping the icons on the screen can be performed without the screen moving from the desired position. Also, a constant torque hinge provides one-handed operation of the screen, rather than pushing a button or flipping a lever to position it.

While constant torque hinges have been available for some time, there are suppliers who continue to introduce new innovations in this technology. One-way, constant-torque hinges, for example, provide constant torque in only one direction of movement against gravity — while providing free-swinging motion in the other. This type of product can be useful in applications such as storage cabinets with large doors. By removing the friction from the hinge in one direction, the door can be easily opened, while torque applied in the other direction holds the door open for access.

Drive and hold: Detent hinges
Detent hinges provide specific motion and tactile feedback. The door or device is opened and locks into place at a preset angle, typically with a distinctive “click” that can be felt. These types of hinges are often useful for lightweight cabinet doors or other devices that must be consistently opened to remain out of the user’s way.

Detent hinges require the user to keep moving the device until it reaches the right position for the working environment — say, at a preset angle of 90 degrees. Bistables are variations on detent hinges and offer a built-in spring mechanism that automatically drives the door or device to the preset angle once the door is open. This functionality is useful for doors, access panels, or covers that must be opened to a minimum angle for easy entry, or to avoid collisions with surrounding equipment.

A controlled opening: Damping hinges
A door, compartment, or other device using a damping hinge means it will move steadily to an open or closed position when force is exerted, rather than popping open or requiring the user to push it closed. This smooth, steady motion is becoming widely preferred in a number of high-end applications, such as car interiors, where the operator expects a more intuitive user experience.

For items, such as eyeglass storage compartments, USB port carriers, or other compartments that are opened and closed, damping hinges add to the user experience and present a high-tech, finely engineered interior.

Minimal effort required: Counterbalance
Counterbalance hinges expand the torque continuum by allowing heavy doors and panels to open or move easily. They incorporate spring mechanisms that store energy when the door or panel is closed. Then, on opening, the energy is released and balances the effort required to move the panel through its range of motion to a fully open position.

For applications where operators are routinely opening and closing heavy doors – industrial copiers are one example – counterbalance technology can help reduce fatigue and improve operator efficiency. For instance, a door with a symmetrical torque hinge may require 56 lbs of effort to open from fully closed to 90-degrees open. By using a counterbalance hinge, the energy required to open the door can be reduced to 3 lbs.

For heavy doors, designers once used gas struts or other such devices, but these are prone to technical problems and failure over time. Counterbalance hinges are a more economical, single-device choice.

The newest counterbalance hinges can also incorporate a latch to support pop-up opening. So, when first opened, a heavy door will lift a few degrees, allowing the end-user to establish a firm grip on the panel. Newer innovations in counterbalance hinges use torsion bar technology to create the counterbalance energy, combined with cam and roller systems to meter out that energy through the full arc of motion.

The result: opening an 80-lb panel feels like lifting a door that weighs 5 lbs. Plus, the effort feels balanced throughout the whole range of opening and closing motions.

Value adds
Designers recognize that every time an end-user opens, closes, or moves a hinged device, the user is exerting a force and undergoing a distinctive tactile experience. New hinge technology that uses the full torque continuum offers designers the opportunity to create more sophisticated solutions for a variety of different applications.

Different types of hinges with different torque profiles can also be combined to satisfy multiple requirements. For example, detent and damping functionality can be combined in a single hinge, so that a door easily opens to a fixed position and clicks in place, and then moves on its own to the closed position when pushed shut.

The key to success is determining the use case for each application, which means deciphering the ideal ergonomics for opening, closing, and positioning a panel or door. To do so, user feedback is essential. Fortunately, well-established hinge suppliers have extensive experience working with end-users to determine the optimum solution and ideal torque for each application.

The author…
James Stroud is a commercial product manager for Southco, Inc. He has over 26 years of experience working in various roles supporting Southco, globally, including in Europe and Asia. In his current role, Stroud manages a portfolio of access hardware products, evaluates industry trends and market needs, and launches new solutions to further expand Southco’s product line.

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Filed Under: Flanges • supports • mounts • brackets • hinges
Tagged With: Southco
 

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