Joystick Required

Dec 1, 2007 12:00 PM, By Jim Cooper

Choosing the right joystick for a video application involves the consideration of a number of device traits

Joysticks have become the user interface of choice for many industrial and high-performance control systems, including motorized wheelchairs, microscopes, construction equipment and submarines. In a security environment, joysticks provide the flexibility and precision needed for camera pan, tilt and zoom control. Security personnel can use the joystick to help focus their attention on video images in order to respond quickly and easily to security issues.

With joystick applications, however, come increased requirements for reliability, durability and overall quality. Manufacturers of front-panel control systems need an input device that matches the sophistication of the underlying control software, that can stand up to continual use and that acts as a cost-effective component of the system.

The joystick, as the primary interface between the user and the system, can literally make or break a system. It presents one of the most prominent visual and physical attributes of a system, conveying a strong impression of the quality of the entire unit. User studies have shown that an interface that feels well-constructed will be treated as a fine piece of equipment, reducing abuse at the same time that it raises the product's image in the mind of the customer.

The intuitive nature of the joystick has made it a natural choice for precision control applications, such as camera control. Joystick manufacturers have expanded upon the basic functionality to create a range of specialized products, adapting everything from core materials to appearance in order to meet the special requirements for each application.

Choosing the right handle, for example, is not just a question of how the unit looks but also how it will be used. Using a smaller handle requires the user to grip the joystick with just the forefinger and thumb. This provides the finest control, and at the same time, limits the amount of force a user can exert in comparison to a large handle, which can be gripped with the whole hand.

Core control and ergonomic features

A joystick typically controls movement in three different ways — forward and back, side-to-side, and in/out. In camera applications, the movements are referred to as pan, tilt and zoom control. The fingertip control is designed to allow the widest possible range of control with the most natural and comfortable motion of the hand, requiring minimal effort. This allows the user to focus on the work, not on the tool.

Pan and tilt motions can be guided or unconstrained as appropriate for the application. The guided option allows the motion to be gently biased toward the cardinal directions (North, South, East and West). It is possible to move the handle away from the poles using slightly greater force. In this way, the joystick guides the user's hand naturally along the normal path of movement while allowing for adjustment when necessary. The third dimension - forward and back in mechanical applications and zoom control in cameras - is accomplished by twisting the handle, which is constructed with grooves, or flutes, for a better grip. The twist should operate within a constrained range of no more than 60 degrees (30 degrees off center in each direction). This allows the user to access the full range of the device without twisting the wrist and greatly reduces the likelihood of repetitive stress injuries.

Interface circuitry

The internal circuitry of the joystick translates the user's motion into electrical signals that can be interpreted by the device control software. In the past, these movements were typically sensed by a potentiometer, a variable resistor in which a sliding wiper blade moves across a fixed contact, mirroring changes in position of the joystick. The problem with a potentiometer-based system is that the sliding component is a mechanical device that is subject to wear and corrosion. More modern systems now make use of contactless technology, through which a field is generated within the joystick at the base of the shaft. As the shaft moves, the sensing part of the circuit detects the change in the field and outputs an analog voltage proportional to the distance moved. Friction and wear are eliminated, and the result is a joystick that can perform up to 5 million cycles without failure.

There are several options for how the joystick transmits position data to the main system. The best joysticks support multiple configurations, starting with standard, orthogonal signals, such as those produced by potentiometer-based systems, and ranging to schemes for mixing signals, such as for operating two motors.

Durability

If the joystick breaks, the entire product is effectively broken.

Durability begins with the basic design, so contactless systems are inherently longer-lasting. The quality of internal components also matters. Look for products where internal components are metal rather than plastic.

An unpleasant but real problem in some environments is the propensity for intentional or unintentional operator breakage or abuse. The use of metal components throughout the device, especially at critical points such as end-stops and the Z-axis mechanism, limits this risk.

Protection against dust, oil and liquids is accomplished by the addition of a neoprene sealing boot. A sealing boot is also useful in protecting joysticks in any environment from the occasional spilling of a beverage.

Reliability and fault-tolerance

Here again, contactless designs have the edge by exuding no gradual drift or “noise” as experienced with potentiometer-based joysticks. The performance of potentiometer-based systems gradually degrades over time as a result of friction and wear on moving parts, leading to unpredictability and loss of precision in the control signal. This “creeping degradation,” which usually manifests as an unstable center, can lead to poor performance of the control product.

Conversely, the most advanced joysticks use contactless designs that employ inductive sensing, making the sensor subsystem immune to mechanical wear.

Some systems require a fault-tolerance capability for safety. If the sensor fails, two things must happen to ensure that the device being controlled returns to a safe, operational state. First, the joystick must know that a fault condition exists. This usually requires the constant generation of an internal redundant “mirror” signal, which can then be compared with the main signal being produced. If a difference is detected, the unit can send a special signal to the controlled device, allowing it to “return to center,” or whichever action is most appropriate.

Customization and installation

The most cost-effective joystick models are not necessarily the cheapest. They are those that can accommodate the application's requirements without the cost of a complete custom solution. Look for vendors that can support branding and design requirements - for example, with custom mold rubber handle sheaths using a company's colors and logo - and can support multiple handle options, output signal configurations and either guided or free motion.

The joystick should also fit seamlessly into the front panel, whether using drop-in or sub-panel mounting. Space is always an issue, and a low-profile sub-panel joystick allows for the design of the thinnest possible panels.

For camera control in a security environment, such as a casino, robustness and simplicity of operation are key factors. Security personnel can use joysticks to pan, tilt and zoom cameras to examine areas of suspicious activity and determine if intervention is necessary.

As a central and prominent component of any control panel, including video surveillance systems, the joystick conveys a brand image and lasting sense of quality of the entire system. The right joystick device achieves a balance among precision, reliability, customizability and price, and allows manufacturers to offer their customers a first-class user experience with long-term dependable performance.

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Jim Cooper is product manager for the Controls Division at APEM, headquartered in France. Cooper has been involved in the joystick industry for nearly 20 years. In 1999, he founded Oliver Control Systems along with two colleagues. The joystick supplier was acquired by APEM in 2005.

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