Rotary encoders with integrated functional safety
Historically, functional safety was based on an all-or-nothing approach. If safety devices such as e-stops, door switches, and light curtains were in the released state, the machine was running. When you pushed an e-stop or interrupted a light curtain, the machine shut down.
Muting, or more technically speaking, the temporary suspension of a safety function, was one of the first procedures to add a level of gray to safety setups. With muting, you can interrupt a light curtain without stopping the machine. It is important to note that muting is only possible under strict and specific conditions. Muting-enabled safety applications fully protect operators while being less restrictive, increasing productivity and uptime.
Zoning is another gray zone that makes safety more flexible without reducing the level of operator protection. Zoning, while already possible using conventional hardwired safety setups, was significantly simplified with the introduction of small and in many cases inexpensive safety controllers. Some of these safety controllers are able to utilize networked safety I/O devices, thus reducing wiring-related issues. By dividing a machine into a number of safety zones, individual sections can be deactivated while other sections remain operational. Not shutting down an entire machine increases uptime and productivity even further.
Safety encoders are the latest addition to any safety engineer’s tool box, widening the safety gray zone yet again. Properly applied, a safety encoder makes possible machine designs that allow operators and maintenance personnel access to machine components. Without such access, a safety shut down would have previously been required. Safety encoders can be used to verify if blades, presses, or similar motor-driven devices are stopped. More advanced solutions can determine if potentially hazardous motion is within a "safe speed range." Some solutions also have the ability to signal safe direction of rotation. Robotics, material handling, and even metal forming applications can benefit greatly from safety encoders.
Just imagine the following. A sheet metal rolling press, properly hard guarded, needs to be cleaned. Previously this required the press to be turned off before granting the maintenance person access to the hard guarded area. While certainly a safe approach, the drawback is that cleaning the entire roll requires the press to be advanced several times. Each time, the system needs to be restarted and shut down. A time consuming, intrusive process.
The fact that the cleaning process takes additional time is not only problematic from a cost and productivity point of view. Much more important is the fact that the intrusive nature of the process creates the temptation to manipulate the safety device to simplify the cleaning process. This gain in time can ultimately lead to potentially dangerous situations.
This video demonstrates how to use a safety encoder to simplify and speed up the cleaning process while keeping the maintenance person fully protected. In addition to ensuring that the press, when accessed by the worker, cannot spin out of control, the safety application further increases the level of protection by ensuring that the press rolls only move in a direction that expels rather than draws in. When all the hard guarding is in place, these limitations are of course removed.
The best safety system possible always protects the worker and never creates any additional work or undue interference. Taking advantage of muting, zoning, and safety encoders, and processing safety logic on a network-enabled safety controller, allows just that.
If you are interested in reading more about these kinds of safety solutions, please visit our sensing and AS-Interface website where you can find videos, application notes, and example configurations for our line of safety controllers.
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