Guard Locking Switches

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Guard Locking Introduction

Overview

Guard locking switches are used to protect hazardous areas where a danger is not immediately removed after a stop request. On many machines removal of power of the motor or actuator will not necessarily cause a reliable and immediate stopping of the dangerous motion. Typical applications are: high inertia rotating machines, fast rotating machines, and machines where high pressure needs to be released from pneumatic valves.

Gates protected with guard locking switches are usually opened on exception basis. For example: to clear a jam or to regularly maintain the machine. This type of switch should not be used for frequent access during normal operation of the machine.

Guard locking switches use a solenoid to activate a lock which blocks or releases the tongue from the switch.

Rockwell Automation offers two different types of guard locking switches:


Power to Lock

When power is applied to the solenoid, the tongue is locked in the switch. When power is removed, the lock is released allowing the tongue to be extracted from the switch.

Power to Release

When power is applied to the solenoid the lock is released allowing the tongue to be extracted from the switch. When power is removed, the tongue is locked in the switch.

Why Use Power to Lock or Power to Release?

  Power to Lock Power to Release
Advantage When the power is removed from the cell after a “controlled stop,” the doors unlock allowing maintenance personnel to go in easily. Power is not applied to the switch all the time, only when the door needs to be opened.
Sudden lose of power does not compromise safety of personnel, as the doors stay closed.
Disadvantage Sudden lose of power will unlock the door allowing personnel to go in the hazardous area and the machine may not be stopped. Loss of power will not unlock the door and maintenance personnel will not be able to go inside the cell.
  

Different methodologies can help decrease the risk that the danger is removed before the operator has access to the hazardous area:

Time based

The risk assessment process and stop time measurement will determine the maximum time for the machine to stop from its normal speed of operation. This time defines the delay between the request to open the gate and the authorization to access the zone by unlocking the gate by energizing (Power to Release) or de-energizing (Power to Lock) the solenoid.

This time delay can be implemented by using any of our time delay units such as the MSR178 or MSR138 safety relay or by software in one of our Safety PLC.


Stop motion

Another methodology is to measure when the motion is stopped. When the no-motion is detected, the lock is released to allow personnel to enter the hazardous zone.

The CU2, CU3, or MSR57 safety relay will be used to detect the motion is stopped.


Safe speed conditions

In some applications, the user may need access while the machine is running at a safe speed. The MSR57P used with encoder technology can handle this application. It will verify the speed of the motion and allow access only if the speed does not exceed a preconfigured limit or otherwise the machine will enter a stop condition.

Typical Sequence of Actions

1. The operator requests to enter the hazardous area
2. A controlled or immediate stop of the machine is initiated
3. The machine is stopped: time delay expired or stop motion detected
4. The gate is unlocked by either energizing (Power to Release) or de-energizing (Power to Lock) the solenoid
5. The operator opens the gate and works in the hazardous area
6. The operator exits the hazardous area and closes the gate
7. The operator restarts the machine
8. The gate is locked by either de-energizing (Power to Release) or energizing (Power to Lock) the solenoid
9. The machine returns to its normal speed

Manual Override

Click to enlarge - TLS-GD2 _(Manual Overide)_02_4C


In the situation where a person is still in the hazardous area, the door is locked and the machine restarts, the TLS guard locking switch product family provides two options for the person to escape the hazard (in addition of an Emergency Stop located outside of the hazardous area):

Option 1: Rear Escape (Not Latched)

A 40 mm push button is mounted on the back of the TLS and is accessible from the inside of the cell. Pushing the rear escape push button releases the lock mechanism inside the TLS guard locking switch allowing the door to be opened, the machine to stop and the person to escape the hazardous area.

Option 2: Flexible Release (Latched)

The flexible release push button accessory is designed to be installed inside the hazardous area to provide a means of escape for personnel who become trapped there. It provides remote access to the manual release mechanism within the TLS-GD2 switch in the event of an emergency situation. The flexible release can be retro-fitted to existing TLS1-GD2 and TLS3-GD2 switches or installed along with a new switch.

The unit is installed at an accessible height next to the guard door, inside the guarded area, while the TLS-GD2 can be mounted outside the guarded area. The flexible release is available with either a 1 m (3.28 ft) or a 3 m (9.84 ft) cable.

Pushing the black button on the flexible release, the movement of the cable activates the release mechanism within the switch, allowing the door to be opened, the machine to stop and the person to escape the hazardous area. The flexible release is then reset using the blue reset handle.


Selection Guide

Product 440G-MT TLS1-GD2 TLS2-GD2 TLS3-GD2 Atlas 5
Click to enlarge - 440G-MT47##_Product_GS Click to enlarge - 440G-T27##_Product_GS Click to enlarge - Atlas 5 GD2_Product 01 GS
Holding Force 1600 N (360 lb) 2000 N (450 lb) 5000 N (1124 lb)
Housing Material Metal Plastic Metal
Locking Mechanism Power to Release Power to Release Power to Lock Power to Release Power to Release
Escape Release None Rear Escape and Flexible Release None Rear Escape and Flexible Release None
Safety Contacts 2 N.C. 3 N.C. 2 N.C. 2 N.C.
Aux Contacts 2 N.O. 1 N.O. 1 N.O. 1 N.O.
Solenoid Monitoring Direct Drive 1 N.O. & 1 N.C. 2 N.C. 2 N.C.
  

Typical Sequence of Actions and Contact Status

Step 440G-MT TLS1 TLS2 TLS3 Atlas 5
Step 1—Hazardous Area Protected Solenoid Power De-energized De-energized Energized De-energized De-energized
Click to enlarge - Step 1 - Hazardous Area Protected_GS Solenoid Feedback A/B Not Available Closed/Open Open/Closed Closed/Closed Closed/Closed
Safety A/B Closed Closed Closed Closed Closed
Aux A (/B⋆ ) Open Open Open Open Open/Open
Step 2—Access to Hazardous Area Authorized Solenoid Power Energized Energized De-energized Energized Energized
Click to enlarge - Step 2 - Access Authorized_GS Solenoid Feedback A/B Not Available Open/Closed Closed/Open Open/Open Open/Open
Safety A/B Open ⋆  Closed Closed Closed Closed
Aux A (/B ‡ ) Closed Open Open Open Open/Closed
Step 3—Access Authorized AND Door Open Solenoid Power Energized Energized De-energized Energized Energized
Click to enlarge - Step 3 - Access Gate Open_GS Solenoid Feedback A/B Not Available Open/Closed Closed/Open Open/Open Open/Open
Safety A/B Open Open Open Open Open
Aux A (/B⋆ ) Closed Closed Closed Closed Open/Closed
Step 4—Gate Ready to Be Locked Solenoid Power De-energized De-energized Energized De-energized De-energized
Click to enlarge - Step 4 - Gate Ready to be Locked_GS Solenoid Feedback A/B Not Available Closed/Open Open/Closed Closed/Closed Closed/Closed
Safety A/B Open Open Open Open Open
Aux A (/B⋆ ) Closed Closed Closed Closed Closed/Open
Step 5—Door Locked and Hazardous Area Protected Solenoid Power De-energized De-energized Energized De-energized De-energized
Click to enlarge - Step 5 - Gate Locked_GS Solenoid Feedback A/B Not Available Closed/Open Open/Closed Closed/Closed Closed/Closed
Safety A/B Closed Closed Closed Closed Closed
Aux A (/B⋆ ) Open Open Open Open Open/Open
  
⋆ Direct drive of the contacts from the solenoid forces the safety contact to open even if the door is closed.
‡ Aux B solenoid auxiliary contact is available only on the Atlas 5 safety switch.

Application Example

Click to enlarge - TLS-GD2 _Example_01_4C


Operating Conditions


Maintenance Conditions


Remarks