Vital / Eden Solves Problem of Unsafe Broken Keyed Switches!

Problem:

Siemens VDO, a manufacturer of automotive instrument panels and infotainment products located in Huntsville AL, was experiencing a safety issue with their circuit board assembly equipment. The machines have a door which allows the operator to load the machine. This hinged door closes from above and must be closed in order for the machine to operate safely. The safety switches installed by the manufacturer were keyed interlock switches which use a mechanical key mounted to the door. This key must mate with a plastic switch that is mounted to the machine. Due to misalignment issues with the doors and repeated opening and closing, the head of the switch had broken, yet the machine continued to operate with the door open!!! Why?

All keyed safety switches are designed so they are held open (i.e. safety circuit is not made) when the key is removed. This is shown in figure 1. When the key is inserted, it rotates the cam to a position where the spring driven ball can move upward, closing the safety contacts in figure 2. Unfortunately, as shown in figure 3, if the head of the switch is loosened or broken, the spring will push up, closing the safety circuit and allowing the machine to run in an unsafe condition.

Solution:

As a solution, Siemens VDO selected the Vital dynamic signal technology developed by Jokab Safety North America. Vital is the heart of a new solution which makes it possible to install/connect many different types of safety devices in the same safety circuit and still achieve safety category 4 according to EN 954-1. The Vital module is based upon a dynamic single-channel concept as opposed to conventional dual-channel safety relays. Up to 30 dynamic sensors can be connected directly in the safety circuit and be supervised by only one Vital module. The Vital therefore replaces several safety relays.

On the door, the conventional keyed safety switch has been replaced by an Eden series noncontact switch. The Eden design which is comprised of Adam and Eva switch pairs, is a noncontact, non-magnetic design for use on interlocked gates, hatches etc. A coded signal is transmitted from the Vital control device via Adam to Eva which inverts the signal and sends it back again. The maximum sensing distance between Adam and Eva is currently 15 mm, which is significantly greater than standard magnetic sensors. Up to 30 Edens can be connected in series and still achieve the same safety level in the safety circuit. It is also possible to connect safety light beams and E-stops in the same safety circuit.

Designed for ease of use, the Eden has an LED for local indication of the switch state. Green is made, Red is open and flashing Red/Green indicates that another switch located prior to the flashing switch on the same circuit is open.

Pictured above, the broken keyed switch is shown below the newly installed Eden non-contact switch. Quick connection, extended sensing range and noncontact operation make the Eden the ideal solution for reliability and ease of use.

System Benefits:

The benefits of this technology include:

• Increased machine safety due to replacement of mechanical key switches
• Simplified safety system design
• Greatly simplified troubleshooting via LED diagnostics
• Potential cost savings due to reduced safety relay requirements for many applications
• Increased machine availability due to non-contact, reliable switch design

Future Use:

The Vital solution should be considered for all safety applications going forward. It provides a cost effective, reliable and easy to troubleshoot solution for all safety applications. It is easily retrofit into existing applications and can accept e-stops, light curtains and safety mats. For further information visit www.jokabsafetyna.com. Article courtesy of Daniel Diehl, Edison Automation, Inc.

See Vital Solution and Eden non-contact, non-magnetic safety switch for more information.