All but the youngest engineers and designers know from experience that no piece of machinery or production line will endure for long without a change or two. Products’ shapes, materials, features, and internal components can change or shift. Production lines can go from making one product to another—or from using one type of machine to a newer one—and management usually wants the changeover done as quickly and inexpensively as possible.
Although purely mechanical changes are difficult enough, changing the wiring complicates everything. When machines are being manufactured, wiring harness redesign (plus retesting and, often, requalification) adds costs in both time and resources. Running new wiring means redesigning conduit runs, plus, again, retesting and often recertification.
These considerations are opening the door to exploring (and often deploying) wireless switches. That’s because wireless switches give manufacturers flexibility in placing and relocating machines. Some applications may also allow the use of completely wireless energy-harvesting switches which work without batteries or power connections.
Wireless switches such as those from ZF and Steute contain small transmitters with a nominal range of approximately 1,000 ft. outdoors and 100 ft. indoors. (Local conditions may reduce those ranges, but signal repeaters can solve such problems.) A receiver connects to the system’s controller. Receivers can be PCB modules for direct integration or 32-channel receiver modules with data ports for interface integration, which may be suitable when creating just one or a few systems. There are also USB receiver modules available for prototyping.
A technician can quickly and easily place-mount an energy-harvesting wireless switch on a forklift, then program it so the driver can remotely open and close garage doors. There’s no need to spend the time and money wiring it into the forklift’s electrical system.
Wireless signal transmitters now fit within the bodies of all but the smallest switches. External switch activation options are limited more by the choice of configurations already being manufactured than by the nature of wireless switching.
That said, there are limits on the complexity of wireless switches. For example, wireless switches, in the interest of low energy usage, only send switch status changes. They are, in that regard, even simpler than momentary switches because they can relay only that they have been activated, not any data on how long a finger or foot may have been on those switches. But the choice to signal only switch-status changes is critical for energy-harvesting switches and is also a tremendous runtime extender for battery-powered switches.
Although these switches don’t latch into one status or another that can be polled—and, in fact, they have no mechanism for polling—this should not present significant obstacles to deployment. Valid last-status readings, for example, can be monitored by controllers that get data from companion wireless receivers.
Innovative engineering can also play a role in expanding the capabilities of wireless switches. For example, a mechanical rocker activating a wireless switch on each side leaves no doubt as to the nature of a new activation.
In some energy harvesting switches, it takes manual activation or the application of a relatively strong external force to trigger signals. That’s because a Chiclet-sized magneto (magnet and coil) inside has to be physically triggered to generate 330 mW—just enough power to transmit a brief wireless signal. Hand remotes, command switches, foot switches, handle switches, and some pull-wire switches are good implementations of energy harvesting, as are some position and limit switches. Other self-powered switches tap into solar power or rely on rectified RF energy, much like an old crystal radio.
Energy harvesting is not an alternative for wireless switches based on magnetic or inductive sensing; these are also available but require an internal battery for power.
Energy-harvesting wireless switches, such as these from Steute, can be push-button, rotary, or require users to have a key for security. Switches are designed to be independent, and controller programming determines their actual functions.
Limitations on Wireless
There are some circumstances in which wireless switches may be inappropriate. For example, any application requiring repeated polling of the switch status is not possible simply because direct polling of wireless switches is not available. But in this case, as mentioned earlier, controllers with reliable memory of the last switch-actuation status may provide an alternative for polling.
There is also some small latency before the receiver recognizes the activation of a wireless switch. Most of this latency is a result of error-checking in the signal path. There is also some minimal latency between switch actuation and generating the radio signal as the powering charge builds internally.
Designers need to be aware of this latency, but it is usually trivial in the context of any operator-actuated switch event. Still, engineers should probably not use these specific switches where rapid-fire process-originated switch activation is required. Also, ongoing, even modestly rapid-fire switching would weigh against using any battery-powered wireless switch. That said, power wiring tends to be more easily available than signal wiring, so wireless may remain a good choice, depending on the application.
ZF/Steute energy-harvesting controls can combine four switches in one handheld unit.
Wireless in Action
Consider the articulating boom of a fire truck ladder or cherry-picker bucket as representative of similar challenges in broadly comparable equipment, from cranes to periscopes. Any of these applications are likely to have need for manual control and an emergency stop or shutdown.
End-of-travel (or mid-travel) switches activated by the motion of a component on a device are often required for safe operation, but these devices are often customized to the needs of the client. Energy-harvesting wireless switches are easy to install at relative rather than fixed points (as in, always X in. from the far end rather than always some different calculated distance along a length). A key benefit for the designers is that this eliminates the need for custom wire harnesses for each build.
With energy-harvesting wireless switches, control becomes easy to extend from the device itself to any number of ancillary or accessory items. For example, a bucket worker along a power line could remotely trigger vehicle warning lights, emergency calls, or upstream-relayed connection commands. All these things can be done with zero wiring reaching along any boom or snorkel.
Failure response: In food manufacturing, feed lines may push ingredients past cutting wires that separate the ingredients into portions for additional handling. When a cutting wire fails, any failure to halt processing creates waste and lost time, so the quicker the situation can be rectified, the better. A wireless switch mechanically connected to the cutting wire can sense a break and trigger an immediate interruption on the line. Because the switch does not add to the power or signal wiring of the production equipment, it becomes easier in the future to make any needed processing reconfigurations.
Failure elimination: It seems redundant to note that wireless switches have no wires, but the point is extremely relevant in production environments where the wiring itself is vulnerable to failure—as in foundries, where casting splashes can destroy wires and cables. Some environments put wiring at risk with deliberate explosions, a risk that wireless devices avoid.
Emergency stops: The best available protection against damage to both personnel and equipment is often the ability to shut things down, hence the widespread use of emergency stops switches, panic switches, and other similar safety standards.
The same ZF/Steute switch hardware is used in several different configurations for ZF/Steute energy-harvesting switches. They can operate in temperatures from −40°F to 185°F, with the rocker switch having a life of at least 100,000 operations and the snap switch lasting at least 1,000,000 operations. The switches also have an IP40 rating.
New equipment, new regulations, or newly perceived risks can often lead to the need to modify these safety controls to add more ways to stop things safely. Adding one or more wireless switches to a factory or assembly line that already includes wireless switches may require as little as an hour, including installation of the switch, updating the controller instructions, and a test.
Even in environments without wireless switches, adding one or more wireless switches, receivers, and control adaptation is quicker than adding another wired switch. This may be why many initial inquiries into deploying wireless switches come from places where there is a new and urgent need to add a stop button or to add them in new places such as supervisory bays. For applications where only those with the proper authority should shut down or start up a process, there are key-operated wireless switches available.
For people designing manufacturing and production equipment, wireless switches in initial designs provide the most benefits when systems are expanded or reconfigured, which eventually happens to all equipment. There are also initial deployment benefits in reducing the need for wiring and conduit runs, including runs to locations off the factory floor.
Wireless switches can be controlled by an operator’s foot, like this energy-harvesting pedal switch from ZF/Steute.
For people designing manufactured equipment, wireless switching adds flexibility in several ways. It lets factories change layouts and assembly lines without changing or dealing with cable harnesses. It puts makes control over fixed facilities mobile, as in controlling access doors from a forklift. It accommodates design updates with more agility, and reduces the number of wiring and connection points that might present after-sale service or repair issues.
The category is relatively young, and designers should not feel limited by the wireless switch configurations that are already in production. Wireless switch manufacturers are willing to work with designers in creating or adapting their products to specific needs.
Ryan Eder, Product Marketing Manager