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VOLUME -22 NUMBER 8
Publication Date: 08/1/2007
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August 2007 Issue
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Joysticks: Crucial Component for Test Systems
Joystick as part of a measuring system control.
By Jim Cooper, Product Manager Controls Division, APEM, Haverhill, MA
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 the flexibility and precision needed by system designers and users alike.
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.
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, adapting 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 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, when compared with a large handle, which can be gripped with the whole hand.
In contrast, assistive mobility applications (such as motorized wheelchairs) sometimes require a much larger grip often 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
A joystick typically controls movement in three different ways — forward and back, side to side, and in/out — in camera applications, referred to 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 with 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 (N,S,E,W). 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° (30° off center in each direction), This allows the user to access the full range of the device without twisting the wrist — greatly reducing the likelihood of repetitive stress injuries.
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, mirroring changes in position of the joystick. The problem with potentiometer-based system is that the sliding component is a mechanical device subject to wear and corrosion. Today's systems 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 outputs an analog voltage that is 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 a failure.
There are several options for how the joystick then 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.
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 like end-stops and the Z-axis mechanism, limits this risk.
In the factory environment, protection against dust, oil, and liquids is ensured by a neoprene sealing boot. That same sealing boot also protects joysticks in any environment from accidental spills of such beverages as soft drinks or coffee.
Reliability & Fault Tolerance
Here again, contactless designs have the edge — 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", 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, utilize contactless 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 can then be compared with the main signal being produced. If a difference is detected, the unit can then send a special signal to the controlled device, allowing it to "return to center", or whatever action is most appropriate.
For mobile applications in particular, radio frequency immunity is important, so that the signal is not affected if, say, a wheelchair moves near a radio signal. Joysticks can provide several levels of RFI immunity, depending on the risk in a given application.
Configurability and Customization
The most cost-effective joystick models are not necessarily the cheapest, but those that can accommodate the application's requirements without the cost of a complete custom solution. Look for vendors, like APEM, who can support branding and design requirements — for example, with custom mold rubber handle sheaths using company colors and logo — and can support multiple handle options, output signal configurations, and either guided or free motion.
Finally, the joystick must fit seamlessly into the front panel, whether the application uses drop-in or sub-panel mounting. Space is always an issue, and a low-profile sub-panel joystick allows for designing the thinnest possible panels.
Joystick cross section shows non-contact sensors.
For camera control in a security environment (such as a casino), robustness and simplicity of operation are the key factors, allowing personnel to focus their attention on the image, not the device, and to respond quickly and easily to security issues.
Precision Camera Control.
The requirements for camera control in the microscopic, the submarine, and the broadcast videography markets are quite different. These products require the highest quality and resolution available. The best joystick models, such as APEM's 9000 series, exceed the finest level of control achievable by the human hand.
Going beyond the core requirements for strength and reliability, a redundant, fault-tolerant design ensures that if a unit does fail, it fails in a safe way. In a wheelchair system, this might mean returning to center and switching off the propulsion. The joystick handle must be ergonomically fitted to the needs of the user, to allow easy grasping, or low resistance to make the handle easier to move.
Joysticks have replaced many traditional lever systems for the control of tractors, loaders, and cranes. Like the machines they control, these joysticks must be built from robust metal and rubber components that can stand up to grueling usage.
Coordinate Measuring Machines (CMM).
CMM developers require the highest level of accuracy and consistency. This is an application where the calibration of the measuring device must be right on target, so the non-degrading contactless option is the best choice. The joystick should offer the same level of control whether on a tabletop or a gantry system.
Entertainment and Gaming.
Finally, industrial joysticks aren't all about work. High performance joysticks are increasingly used to control sophisticated arcade games and entertainment systems. One example is a mechanical "bull" installed in barrooms, which allows one person to control the action with a joystick, in an attempt to "throw" a friend off of the bull.
As a central and prominent component of any control panel, the joystick conveys the 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 OEMs to offer their customers a first-class user experience and long-term dependable performance.
For more information, contact: APEM, P.O. Box 8288, Haverhill, MA 01835-0788
978-372-1602 fax: 978-372-3534 or 978-372-9516 E-mail: firstname.lastname@example.org Web:
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