Joysticks And Their Applications

Joysticks have become the user interface of choice for many industrial and high-performance control systems. For applications as diverse as security-camera surveillance, motorized wheelchairs, microscopes, construction equipment, and submarines, joysticks provide

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With these 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 their underlying control software, can stand up to continual use and is a cost-effective component of the overall system.

The joystick, as the primary interface between the user and the system, can literally make or break the system and it presents one of the most prominent visual and physical attributes of the system, conveying a strong impression of the overall quality of the entire system. 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.

Selecting the right joystick

The intuitive nature of the joystick has made it a natural for precision control applications. Joystick manufacturers have expanded upon the basic functionality to create a range of specialized products and have adapted everything from the core materials to the overall look and feel to meet the special requirements for each application.

Choosing the right handle, for example, is not only a question of how the unit looks but also how it will be used. 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.

In contrast, assistive mobility applications, such as on motorized wheelchairs, sometimes require a much larger grip using a sphere or a ball to satisfy the users ergonomic needs. Devices can even be modified to accommodate chin or forehead activation.

Core control features/ergonomics

A joystick typically controls movement in three different ways: forward and back, side to side, and in/out. Camera applications refer to it as pan, tilt and zoom. The fingertip control is designed to allow the widest range of control possible with the most natural and comfortable motion of the hand and 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 axes: 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, zoom in cameras, is accomplished by twisting the handle which can be formed 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 fixed contact that reflects changes in position of the joystick. Potentiometer-based system has a sliding component, a mechanical device, that is subject to wear and corrosion.

More modern systems now make use of contactless technology, in 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 sends an analogue voltage proportional to the distance moved. Friction and wear are eliminated and the result is a joystick that can perform up to five million cycles without failure.

The joystick uses several options to transmit 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 and no-contact 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 like end-stops and the Z-axis mechanism, limit this risk.

In the factory environment, protection against dust, oil and liquids is ensured by a neoprene sealing boot. Of course, a sealing boot is also useful in protecting joysticks in any environment from the occasional spill of a soft drink or coffee.

Reliability and fault tolerance

No-contact designs have the edge in reliability with 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 which lead to unpredictability and loss of precision in the control signal. This creeping degradation, usually manifested as an unstable center, can lead to poor performance of the control product and potentially dangerous situations.

Conversely, the most advanced joysticks, such as the 9000 Series joysticks offered by APEM, use no-contact designs that employ inductive sensing, making the sensor subsystem immune to mechanical wear.

Some systems require fault tolerance 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 is compared with the main signal being produced. If a difference is detected, the unit can then send a special signal to the controlled device that allows it to return to center or whatever action is most appropriate.

For mobile applications in particular, radio frequency immunity is important. A wheelchair that moves near a radio signal must not be affected by the signals. Joysticks can provide several levels of radio frequency immunity depending on the risk in your application.

Configurability and customization

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

Installation and manufacturing features

Finally, the joystick you choose must fit seamlessly into the front panel, whether you are using drop-in or sub-panel mounting. Space is always an issue, and a low-profile sub-panel joystick allows you to design the thinnest possible panels.

Jim Cooper founded Oliver Control Systems, a manufacturer of joystick products, which was bought by APEM.