Choosing the Right Joystick

Joysticks have become the user interface of choice for many industrial and high-performance control systems. Joysticks provide the flexibility and precision needed by system designers and users alike. 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.

As the primary interface between the user and the system, the joystick, 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. The intuitive nature of its use makes 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 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 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 degrees (30° off center in each direction), this allows the user to access the full range of the device without twisting the wrist — 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, 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 systems is that the sliding component is a mechanical device subject to wear and corrosion.r 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.

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.

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 spilling of a soft drink or coffee.

Reliability & fault tolerance

Some systems require fault tolerance for safety.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. Joysticks can provide several levels of RFI immunity, depending on the risk in your application.

Contributed to Control Engineeering by Jim Cooper, product manager, controls division at APEM Components Inc. APEM website .

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