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Video: Mechanics Versus Electronics - A Comparison Of Safety Components
Torque overloads can have different causes. For example, they are the result of operating errors or malfunctions in the electronics. To protect the machine applications and avoid expensive downtimes, machine and system builders use various safety devices. In addition to purely mechanical components, many electrical variants can also be used here. A comparison of the two functional principles shows that mechanical safety components have numerous advantages over electronic safety components.
Speed is a crucial factor
This is particularly evident in the response time of both variants: after all, speed is a decisive factor in this context. The faster the control switches off or the component interrupts torque transmission, the less consequential damage to components or the entire machine.
This can be illustrated, for example, from the following scenario from practice: An overload occurs in a machine as a result of a blockage or collision. With electronic monitoring, the information about the torque overload must now be supplied to the engine control. On average, 5 ms to 7 ms elapse. During this time, the control tries to increase the torque further in order to reach the setpoint. In the optimal case, another 10 ms elapse between the signal arrival at the engine control and the engine shutdown. As a result, it takes a total of at least 15 ms to 17 ms from a blockage in the machine to engine shutdown.
A mechanical safety coupling separates the input and output side from each other within 3 ms to 5 ms - i.e. in one third of the time of an electronic shutdown. The 10 ms to 14 ms, which mechanical protection reacts faster, make a decisive contribution to preventing machine and tool damage.
Another advantage of mechanics over electronics is the lower number of possible sources of error. Many sensors are required to protect the systems with electronic monitoring systems as well as possible. In addition to the sensors, torque measuring devices must be installed at important positions within the system. This structure of several and different security components harbors risks and sources of error and must also be checked and maintained regularly. The advantage of a mechanically switching safety clutch at this point is that only one safety clutch is required per axis in the system and therefore only this has to be monitored.
Easy to use
In addition, they score with their simple handling and easy adjustment. If, for example, excessive moments of inertia are present in the entire drive train, so that the clutch would trigger when braking and accelerating, the release torque can be easily adapted to the circumstances due to the existing setting range. Thanks to the variable installation options, the clutch can also be used in the drive train where the likelihood of an overload is greatest.
With its various series of mechanical safety couplings, R + W Antriebselemente GmbH offers the right solutions for a wide range of applications. The torque-limited couplings are available in different model series, sizes and variants and are generally characterized by their high precision. Like all safety couplings from R + W, they work according to a spring-loaded ball detent principle and with specially developed disc springs. In the event of an overload, this ensures that the input and output are separated in the millisecond range and low residual friction. Safety clutches from R + W are set in the factory to the required torque (release torque). However, this can easily be adapted to changing requirements within the possible setting range.
The classic model series (SK / ES) is suitable for torques between 0.1 Nm and 2800 Nm. The various models in the series are available for direct or indirect connection, with a clamping hub, conical clamping ring or feather key connection as well as a torsionally stiff metal bellows or a vibration-damping elastomer version. Depending on the requirements, the model series is also available in different functions - with angle-synchronous re-engagement, as a snap-in clutch, in a release version and as a locked version.
Safety clutches in lightweight construction
In order to meet the constantly changing market requirements, such as lower mass moments of inertia, higher operating speeds or more efficient processes, R + W also has lightweight safety couplings, which are particularly characterized by their high power density. The lightweight safety couplings of the SL series are also available in different functions and in different versions for use in direct or indirect drives.
Industrial safety couplings of the ST series can be obtained as standard for torques up to 250,000 Nm. The robust and powerful couplings of this model series are also available in many designs and sizes for different requirements and applications. Numerous options and special designs, such as safety couplings for even higher torques, complete the R + W range.
When it comes to protecting machines and systems and thus avoiding downtimes, fractions of a second can be decisive. Mechanical safety couplings not only give users a valuable lead in terms of time, they also make an important contribution to increasing process safety and score with their ease of use. (sh)
SPS IPC Drives 2016: Hall 3A, Stand 320
* * Dirk Hasenstab works in marketing and sales at R + W Antriebselemente GmbH.
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