1. What is a 3-position enabling device?

A 3-Position Enabling Device (3PE) is a manually operated protective device that is widely used with industrial robots. 

A 3PE is active only when the robot is in manual mode. As a manually operated protective device, it allows robot movement when it is continuously activated (held in the center-ON position).

When de-activated (released or fully compressed), the enabling device stops operation and initiates a Category 2 safeguard stop (according to IEC/EN 60204-1). After fully releasing the 3PE, the control system allows motion to be initiated when the user presses the 3PE to the center-ON position.

In the UR20 robot arm, 3PE functionality is built into the 3-Position Enabling Teach Pendant (3PE Teach Pendant) shown in Figure 1 below.

Figure 1: How to hold the 3PE Teach Pendant

2. Why is a 3PE and mode selection required for ur20?

Added risk due to longer reach, higher payloads and greater operating torques and speeds, associated with the bigger UR20 (and UR30) robots, require the use of a 3PE Teach Pendant.

As a requirement, a 3PE device or a 3PE Teach Pendant must be used with an operational mode switch. This requirement ensures safety, consistency and optimal performance.

3. Enhancing usability with a tool mounted Freedrive button

Using the 3PE Teach Pendant while positioning a welding torch with one hand can be difficult depending on the implementation method.

For example: Many UR20 welding applications use a touch to teach programming model, that requires the operator to manually position the welding torch to define waypoints.

To enhance the user experience, a new method of enabling Freedrive with safety inputs, was introduced in PolyScope 5.13. This function enables Freedrive in manual mode without requiring the user to activate the 3PE on the Teach Pendant.

The Freedrive input is intended to be used in conjunction with a dual channel switch mounted onto, or near to, the tool and wired into a pair of safety inputs in the controller (Figure 2). Mounting the Freedrive input onto or near to the tool is critical to ensuring the user can press the Freedrive button and move the robot at the same time. 

Proper implementation and usage of a Freedrive button should be factored in when performing a risk assessment.

Figure 2: Enabling Device -Wiring Diagram

Figure 3: Freedrive selection in the Safety IO configuration

4. Using THE 3-position enabling devicE for work cell safety

Many applications require the 3PE signal to be integrated into the safety system for the entire work cell. One way to access the 3PE signal is by using the Robot is not stopping function under the safety output. (Figure 4)

The signal is High when the robot is stopped or in the process of stopping due to an emergency stop or safeguard stop. Otherwise, the signal is Low.

Figure 4: Robot Not Stopping Output Selection

5. Manual mode vs. Automatic Mode

When using the 3PE Teach Pendant , the robot is operating in manual mode or automatic mode. The hybrid mode is not be supported.

Manual Mode or Teach Mode is used for configuring and programming the robot.

Automatic Mode is used for running the program.

* The Speed Slider on the Run screen can be enabled in the PolyScope Settings.
** The robot operates at Manual Reduced Speed unless Manual High Speed is activated.

6. Testing and Running Programs:

To test or run a program, operators have two options:

• Hold the 3PE button in Manual Mode: For testing purposes, operators can hold down the 3PE button in manual mode while the robot follows the programmed instructions. If the button is released during operation, the program stops.
• Switch to Automatic Mode: When ready to run a program, operators can switch the 3PE to automatic mode to initiate program execution.

Note: The maximum speed of the robot is limited in Manual Mode to 250mm/s, unless high speed mode is enabled. The program can run faster in Automatic mode based on how the program is written.

7. Selecting Operational Modes

The UR20 with 3PE Teach Pendant offers the following methods for selecting operational modes:

a. Using a mode selection switch

1. Wire the mode selection switch into the yellow safety I/O in the controller.
   
   Figure 5: Connection of the hold to run switch and mode selector.
   
2. Navigate to the Installation Tab and select Safety I/O
3. Configure the Operational Mode Input:
   • The robot is in Automatic Mode when the Operational Mode Input is low.
   • The robot is in Manual Mode when the Operational Mode Input is high.
   • Ensure compliance with ISO 10218-1: article 5.7.1 for physical mode selectors

Figure 6: Configuring the safety I/O in PolyScope

b. Using the Teach Pendant

1. In the Header, select the profile icon:
   
   • Automatic indicates the operational mode of the robot is set to Automatic.
   • Manual indicates the operational mode of the robot is set to Manual.
   • PolyScope automatically switches to Manual Mode when the Safety I/O configuration with Three-Position Enabling Device is enabled.

Figure 7: PolyScope 5 in Manual Mode

Figure 8: PolyScope 5 Automatic Mode selection

Figure 9: PolyScope 5 in Automatic Mode

c. Using the Dashboard Server

1. Connect to the Dashboard server.
2. Use the following commands:
   • Set Operational Mode Automatic
   • Set Operational Mode Manual
   • Clear Operational Mode
   • Refer to Universal Robots support for more information on using the Dashboard server.

Conclusion

Following these guidelines and leveraging the new safety function, welders and operators can maximize  UR20 and UR30 potential, while ensuring safety and efficiency. Whether teaching, validating, or running programs, the 3PE Teach Pendant plays a pivotal role in optimizing robot operations and operator safety.

References

Support article for 3PE Teach Pendant

3PE Teach Pendant Manual e-Series

3-Position Enabling Device and Mode Selector- Connection and Configuration for CB3 and e-Series