Determining the Right Level of Torque When Specifying Hinges

November 4, 2019 Rachel Pilgren-Kane

Counterbalance technology can help reduce fatigue and improve operator efficiency by making heavy lids and panels on large pieces of equipment, such as industrial copiers and blood centrifuges, feel lightweight.

By James Stroud, Commercial Product Manager, Southco, Inc.

One of the most common and widely used devices in today’s world is the door hinge. It is so ubiquitous that it’s often overlooked and in many cases, taken for granted. On closer consideration, however, industrial and systems designers often discover that hinge technology offers a sophisticated range of functionality that can be useful to improve the operation of the systems they design.

When designing an application that hinges two panels together, whether it’s for a simple enclosure or a large, complex piece of medical equipment, choosing the appropriate level of torque is essential to creating reliable operation and an intuitive end user experience.

Understanding the different levels of torque and which applications they are best suited for can help device and systems designers choose the hinging solution with the appropriate level of torque, in order to enhance the end user experience and reliability of the application.

Understanding 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 is based upon the weight of the door, the travel distance or arc of motion from closed to open (and back again) and whether there is a desire to move the panel to one point in the arc of motion and hold it, or always have the motion go from fully open to completely closed.

Today, leading 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 choose from different options within this continuum to satisfy functional and ergonomic requirements and supply touch point experiences that convey unique impressions of quality and functionality. 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 thus creating a positive perception of the inflight environment. In addition, constant torque hinges designed and manufactured with high-quality materials retain the desired resistance after thousands of flights, without maintenance or replacement of parts.

Selecting the right hinge with the right torque

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 in order to select the right hinge with the right 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 does require the user to exert some force, but prevents the door from falling. As a door panel’s weight approaches 15 to 20 pounds, and upwards of 500 pounds, counterbalance technology begins to provide a more effective option. With a counterbalance hinge, the hinge prevents the door from falling and makes that door feel lighter so that the end user is not putting towards any extra effort into overcoming the door’s weight to open or close it.

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.

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. In this concept, opening an 200-pound engine hood for instance feels like lifting a door weighing just five 10 pounds, and the effort is balanced through the whole range of opening and closing motions.

Direction of movement: For direction of motion, it’s important to determine whether the panel or door is hinged vertically or horizontally. If it’s hinged vertically and moves side to side, it is not working against gravity the same way a horizontally hinged panel does, which needs to move up or down. In some situations, a horizontally hinged door may also need to be moved and held in 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 higher, so a constant torque or counterbalance hinge might make more sense, especially wen the technician is working underneath a door that needs to be held open overhead.

Constant torque: Hold securely at every position

Constant torque hinges provide intuitive movement of a device so that the amount of effort to move it is just enough to respond to deliberate motion, while holding it in place for more casual or touch interactions. A now-common example of this is a touchscreen monitor at a checkout counter, in a supermarket for instance.

A constant torque hinge attaching the monitor to the base lets the cashier or user tilt the monitor up and down for optimum viewing and interaction. Tapping the icons on the screen can be performed without the screen moving from the desired position. In addition, a constant torque hinge provides one-handed operation of the screen, rather than pushing a button or flipping a lever in order to position it.

Constant torque positioning hinges, like Southco’s E6 Series, provide reliable positioning with consistent operating efforts, and eliminate the need for secondary support components to hold doors or panels in position.

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 instance, 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.

Detent hinges: Drive and hold to presets

Detent hinges provide very specific motion and tactile feedback: The door or device is opened and locks into place at a preset angle, usually 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 — for instance, a preset angle of 90 degrees.

A variation on detent hinges is called bistable, which contains 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.

Damping hinges: Controlled opening

With a door, compartment or other device using a damping hinge, it moves steadily to the open or closed position when force is exerted, rather than popping open or requiring the user to push it all the way 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 like eyeglass storage compartments, USB port carriers and other compartments that are opened and closed, damping hinges add to the impression of a high-tech, finely engineered interior — a crucial element that many designers seek to achieve.

Counterbalance: Move heavy objects with minimal effort

Counterbalance hinges expand the torque continuum by allowing heavy doors and panels to be easily opened and moved. They incorporate spring mechanisms that store energy when the door or panel is closed; upon 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 pounds of effort to open from fully closed to 90-degrees open. Utilizing a counterbalance hinge instead, the energy required to open the door can be reduced to 3 pounds.

In the past, to enable the opening of heavier doors, designers would incorporate gas struts or other devices, which are prone to technical issues and failure over time, to provide the added lift. Counterbalance hinges now provide a more economical, single-device solution. And the newest counterbalance hinges can incorporate a latch to support pop-up opening: When first opened, the heavy door lifts a few degrees, allowing the end user a firmer grip on the panel when they are trying to move it to the desired position.

For applications that require the lifting of larger lids and panels, counterbalance torsion spring systems like Southco’s CB Counterbalance Hinge series can be used to neutralize the weight of heavy doors, providing motion control for easy and safe opening and closing.

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. In this concept, opening an 80-pound panel feels like lifting a door weighing just five pounds, and the effort is balanced through the whole range of opening and closing motions.

Adding tactile value to “open and close”

Leading suppliers of hinge technology have recognized that every time an end user opens, closes or moves a hinged device, the individual is both exerting force and experiencing a distinctive tactile experience. The advent of more hinge technology that incorporates a range of torque options and touch point experiences gives industrial designers a new set of tools to enhance the user experience and thus, the impression they have of the devices being used.

This torque continuum offers the opportunity to create more sophisticated solutions. Different types of hinges with different torque profiles can 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 in a controlled fashion to the closed position when it is pushed shut.

The key is to determine the full usage case for each application– what ergonomic effort should be expended to open, position and close a device, what user feedback is needed or desired to accomplish this motion effectively and on a repeatable basis. The ability to fully customize the torque level allows the designer to ultimately define what the end user experience will be. The industry’s leading hinge suppliers have extensive experience working through these usage cases to help define the optimum solution and can provide in-depth expertise to cost-effectively configure the right hinge with the right torque for each application.

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