Joysticks have become the user interface of choice in many gaming and broadcast applications
BY JIM COOPER
APEM
Haverhill, MA
http://www.apem.com/
Joysticks have become the user interface of choice for many high-performance control systems in a variety of markets. For applications as diverse as gaming, broadcast, security, microscopes, 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.
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, 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, in comparison to 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 ergonomic needs. Devices can even be modified to accommodate chin or forehead activation.
Control features/ergonomics
A joystick typically controls movement in three different ways: forward and back, side to side, and in/out—referred to in camera applications 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.
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. The problem with potentiometer-based systems is that the sliding component is a mechanical device 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 outputs an analogue 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 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.
Durability
If the joystick breaks, the entire product is effectively broken. 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.
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 use contactless designs that employ inductive sensing, making the sensor subsystem immune to mechanical wear.
As the primary user interface, a joystick can literally make or break a system
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. Joysticks can provide several levels of RFI immunity, depending on the risk in your application.
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 exceed the finest level of control achievable by the human hand.
Entertainment and gaming
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. ■
For more on joysticks, visit http://electronicproducts-com-develop.go-vip.net/controls.asp.
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