Home / CNC Training / Lesson 2: Crash & Recovery
CNC Training Module: Section 2.7: Fast Start - Crash & Recovery

Lesson 2: Crash & Recovery

This tutorial provides a detailed guide on the crash and recovery process for CNC machines, specifically focusing on the differences between closed loop and open loop systems. The instructor explains the implications of each system type when a physical crash occurs and demonstrates the recovery steps necessary to restore machine functionality. Key content covered includes:

  1. Introduction to crash recovery processes for CNC machines
  2. Explanation of closed loop vs. open loop systems
    • Closed loop: Features a feedback loop to prevent damage during a crash
    • Open loop: Lacks feedback and may continue moving against a physical barrier until stopped manually
  3. Demonstration of a physical crash using a closed loop system (Maverick four by eight)
    • Turning off soft limits for demonstration
    • Observing the system’s response to hitting a physical barrier
    • Automatic deactivation of the motor to prevent damage
  4. Steps to recover from a crash in a closed loop system
    • Powering off the machine
    • Waiting 10-15 seconds before rebooting
    • Homing the machine after reboot
  5. Explanation of the crash recovery process for an open loop system
    • How the system continues to attempt movement during a crash
    • Use of the emergency stop (e-stop) switch to halt all motion
    • Reactivation of the system by deactivating the e-stop and rehoming the machine

Main purpose: To educate users on the crash and recovery processes specific to closed loop and open loop CNC systems, ensuring they understand how to properly handle physical crashes and restore machine functionality.

Key takeaways:

  • Understanding the differences between closed loop and open loop systems in CNC machines
  • Procedures for safely recovering from a crash in both system types
  • Importance of using the emergency stop switch in open loop systems
  • Steps for rebooting and rehoming the machine after a crash for continued operations

Video Summary

Remember This Checklist:

  1. Understand the difference between open loop and closed loop systems
  2. Learn how a closed loop system reacts to physical crashes
  3. Know the procedure to reset a closed loop system after a crash
  4. Identify how an open loop system behaves during a crash
  5. Understand the steps to recover from a crash in an open loop system

Introduction to Crash and Recovery (0:00-1:21)

0:00-0:05 – Introduction to the training video
0:05-0:14 – Overview of the crash and recovery process for the system
0:14-0:36 – Explanation of open loop and closed loop systems
0:36-1:00 – Details about closed loop systems and their feedback mechanism
1:00-1:21 – Description of open loop systems and their lack of feedback

Demonstration of a Crash with Closed Loop System (1:21-2:45)

1:21-1:38 – Introduction to the crash demonstration using a closed loop system
1:38-1:56 – Explanation of turning off soft limits for the demonstration
1:56-2:07 – Moving the Y axis to simulate a crash against a physical barrier
2:07-2:45 – Observation of the system’s automatic shutdown upon hitting the barrier

Resetting the Closed Loop System (2:45-3:35)

2:45-3:00 – Explanation of the system’s deactivation after a crash
3:00-3:15 – Procedure to reset the system: power off and power on
3:15-3:35 – Waiting period recommended before rebooting the machine

Operational Status After Reset (3:35-4:29)

3:35-3:50 – Homing the machine post-reboot to restore operational status
3:50-4:05 – Confirmation of successful homing routine completion
4:05-4:19 – Summary of steps taken for closed loop crash recovery
4:19-4:29 – Introduction to handling crashes in open loop systems and their recovery procedure

Full Video Transcript

Introduction to Crash and Recovery (0:00-1:21)

0:00-1:20: “Hey, hey, welcome to another training video. Today we’re gonna be performing another crash and recovery process, and that is what happens to the system and how do you recover when you actually have a physical crash with the machine. Now, before we get to actually performing a physical crash on the system, I want to explain two things, um, about the machines themselves. We manufacture two types of, you could say, uh, controller systems when it comes to how the motors are receiving information to move along the axes. Uh, one is a open loop and one is a closed loop system. The closed loop systems are everything from a maverick four by four and larger. Uh, they have two wires going into each motor because one wire sends communication to the motor, and then the second wire is the motor sending information back to the driver. So if by chance the motor cannot progress past a certain point because of a physical barrier, it’s going to inform the driver to simply shut off so that it stops moving that access. Now on an open loop system, that’s the Maverick three by five machines. Um, it doesn’t have that feedback loop. There’s only one wire per promoter. So if it does hit a physical barrier, um, it can keep trying to push past that physical barrier. It won’t damage anything, but it won’t stop until you press the emergency stop switch.”

Demonstration of a Crash with Closed Loop System (1:21-2:45)

1:21-2:08: “So let’s, let’s show you what happens when we actually crash a physical barrier with a closed loop system here on the Maverick four by eight. Now what I have done here is I’m simply going to move the um, axis of the Y axis and I’ve turned off the soft limits. We had a dedicated video that shows how that protects you, you know, from hitting physical barriers. Well, I’ve deactivated those and so that we can demonstrate what we’re we’re about to do today. Regardless if this is actually your tool or your spindle actually running into something here on the table, um, this will kind of simulate that of it, of it, of it hitting a physical barrier. So I’m still gonna move this up against the side of the carriage and you’ll see it, um, bump up against the side of that gantry. Um, and it will automatically switch off when we do so. So here it is.”

2:13-2:45: “So we can see it just hit that physical barrier and because the motor was unable to progress past that surface, um, it sent signals back to the driver and the driver is now deactivated. So if I try to actually move that axis at all, okay, the y axis, it’s completely deactivated, so I won’t be able to proceed on with anything until we’ve reset the system to get that driver, um, back on track. And to do that, we simply power off and power on the machine again and rehome the system. And this is all back on track ready to use.”

Resetting the Closed Loop System (2:45-3:35)

2:43-2:45: “And this is all back on track ready to use.”

2:49-2:58: “I will usually wait about 10 or 15 seconds anytime I’m rebooting the machine just to let all the electronics completely shut off before we turn them back on.”

3:01-3:09: “With the system powered on, we can now home the machine like we normally would. We’ll speed up this process for you in the video.”

3:19-3:29: “Now that the system has been rebooted and the homing routine is complete, um, we are operational and we can continue on with any other setups or operations that we wish to proceed with.”

Operational Status After Reset (3:35-4:29)

3:35-4:29: “So those are the steps and procedures that we take. If we do a physical crash with a, with a closed loop system, if we perform a physical crash or accidentally perform a physical crash with a open loop system, uh, it’s very similar but just slightly different. Instead of the machine just, you know, turning off the driver like we saw, um, earlier while it’s hitting a physical crash, it’s going to continue trying to move in that direction. And so we just push the e-stop switch, okay, now we’ll stop all motion in the middle of that physical crash, we can then deactivate the estop switch and instead of having to turn the system off and then on again, because we haven’t tripped any drivers like a closed loop system, all we have to do for an open loop is rehome the machine. So just go press that home system button. Once it’s done with this, with the homing routine, we are back on track just like this system was when we did a full reboot.”