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Machine designers are always looking for ways to provide machine safety to reduce damage caused by accidental collisions which can lead to replacement costs and lost production for the end customer. As machine designs today are increasingly reaching new mechanical and productivity limits, the need for fast, comprehensive protection is becoming even more important. The Mechanical units offered by ComInTec address that need and offer distinct advantages in a wide range of applications.

Mechanical

The mechanical torque limiter / overload safety coupling is designed to protect key components of machinery and systems from overloads. These devices will overload when a pre-set calibration torque is reached, as this setting is lower than the breaking point of the weakest drive component. The units are simple to calibrate and can be easily adjusted to suit different areas of the machine.

Why is electrical sensing seen as an economical alternative?

Electrical

Electronics and control technology have advanced at the same pace as the development of today’s high speed and precision machines, leading many customers to believe that a lower cost option is to control torque levels electrically by monitoring the motor current or temperature.

Increasingly, motor current dependent systems are being used though there are 2 distinct disadvantages when compared to the mechanical torque limiter.

1)          When an overload occurs and there is a sharp increase in the torque because of a crash situation a signal from the monitoring circuit must first be sent to the controller. The controller then attempts to increase the torque until it reaches the preset value which can in most cases take the same amount of time again before the drive is actually stopped. Depending on the application, this can be anywhere from 15-20 milliseconds. 

A mechanical limiter will allow for instant disengagement of the driver from the driven and when installed in a strategic position will significantly reduce the reaction time to 1/3 of that offered by the electrical sensing. 

Another key advantage is that complete disconnection will, in addition, remove the impact from the shock of the collision, in particular where high speeds and inertias are involved. With electrical torque control the drive will eventually be stopped but due to the shock impact present a high level of damage can still occur.

2)          Another disadvantage of the electrical method is the number of areas where a failure can occur. Electrical methods generally require a number of sensors to ensure maximum protection, and in addition, customers may use additional torque sensing devices as secondary systems. This complex arrangement only adds to the costs and potential failure points.

A mechanical torque limiter can be used simply, one on each axis only, providing complete disconnection between the driver and driven with fast easy adjustment possible over a broad range.

Disadvantages of Electrical:

10-15 millisecond reaction times
Multiple sensors required
Unsuitable for high speed or large inertias
Complex arrangements                              

Advantages of Mechanical:

1/3 of the reaction time
1 unit per axis only, can be positioned anywhere on the drive train.
Simple set up with easy adjustment
Potentially lower overall costs
Absorption of shock loads
Use at high Speeds
Better reliability
Use in heavy environments
Excellent configuration versatility

How will the New EN ISO 13849 standards impact machine designers?

The common categories of inspection for the safety of machinery will be upgraded to a higher level, in accordance with EN ISO 13849 standards. To meet this standard, the designers of machines and systems will need to allow for the installation of suitable control and/or safety systems.

 ComInTec torque limiters, designed in accordance with  modern engineering practices, are proposed as mechanical components required for installation within the drive chain in order to maximize the safety level of the machine, according to the new EN ISO 13489 -1 standard. 

Therefore, the aim is to prevent and avoid damage or deformation of mechanical parts due to sudden or accidental overload, reducing the probability of failure and unproductive downtime.
The new legislation compliance date has been extended until late 2011, due to the difficult and unclear interpretation. The current standard EN 954-1 remains in force up to this date.