RSlogix 5000 Servo – Proper Start Up Control 

Our goal is to provide the best education of controlling a servo and show the importance of the order of operation in which the RSLogix 5000 instructions should be programmed, this is hinted at many times by Rockwell in their software but unless you have experienced reasons why then it is not that obvious.

One hint would be if you have ever used the motion axis direct commands to control a servo for troubleshooting or testing. The control insists that we start, stop, reset in a certain order but don’t take those instructions I named literal, these are examples and are going to be talked about below to give you the best training for this.

Next hint that is known in the electrical industry can be compared to the same function of a frequency drive or VFD controls. Meaning, if you have ever had an issue where you commanded a start to a drive-through programmed logic and seen that the VFD did not start then you may be aware of this reason. You cannot start a drive that has a start command held and a stop of some sort has not been cycled.

A similar instance of this happens with abnormal events in a processor like a processor fault or a processor being swapped from remote run to program mode….just an example but there are many.

Abnormal process upsets happen in day to day operations of machines which can come from many different sources. Like any plc controls, Rockwell Automation controls are dependent on what hardware and software you are using the application so it is best to have a base understanding of your system. Ever component no matter who makes it stands a chance of process interrupts.

What I have done here in this article to help best illustrate this is to make a video which talks my best practices when it comes to servo controls and why, this video is a short but to the point to help save you time. If you have any questions then feel free to reach out to me.

In this video, I will justify why I use a specific sequence of operations and its benefits. I will also shed light on the reason why I use an “Off” at the beginning of the operation while using RSLogix 5000 Servo Control. I will take you through a detailed walkthrough of my preferred sequence and the advantages of using the same.

Instructing an Axis OFF in RSLogix 5000 or Studio 5000

In most of the systems that you come across in the industry, you will notice that the sequence starts with an “On” at the beginning. You will also come across the same sequence if you have been trained by Rockwell in some instances. with that being said, they do not cut the system Off before they do an On.

However, as mentioned above, I have always chosen to issue an Off statement up-front because you are uninformed about the present state of the controller.

In the instance shown in the picture, the very first step of the state machine control is to make sure the servo is not faulted or the sercos ring then the motion group is synced and after all that has happened and the HMI_ServoSystem_ProcessStart is pressed then it instructs an MSF to make sure the servo is turned off before any other servo command is done. After the MSF instruction has finished and the Axis status is off then it will transition the state logic to 1.

For instance, there might be a situation where you could have lost communications with the controller due to an anomaly or any unprecedented situation. It is also not possible for you to know for sure whether the servo controller has not been told to run already or to cut on. It might have stayed in the on state for other controller or program reasons as well, which you were unaware of.

It is in my opinion, it is crucial for you to cut it off in order to control it to limit the risk of entering into an uncontrolled state.

To put it in simpler terms, it is just like a drive holding an On bit, or a drive holding an Active bit at all times. Thus, it fails to run when you try to start it. Therefore, in order to avoid any instruction faults, it is imperative for you to cut it Off.

Making Sure The Servo Axis Does Not Have a Fault

Once that’s done, I go to the next part to control a Reset as shown in the image above. I always separate my Resets because in cases of faults or shutdowns, like a Motion System Shutdown, then the Shutdown status bit will come On thereby issuing the Shutdown Reset. However, if the Shutdown State is proper, and there is no Shutdown, but the Axis is faulted, I would only want to reset my Axis.

Therefore, I am not performing both the actions in a single situation. I am only performing the one I need to.

Instructing the Servo Axis to Turn ON

In the picture above, if there is an instance where there is no Axis fault or a Shutdown Status, then I can either go immediately to a state where I can Home it if I wanted to, or I can cut the Servo On. In such a situation, I would first like to monitor the Bus of my Servo controller to ensure it is healthy.

I would then ensure that my Axis is not in a faulted state. I would, at this point turn the servo On. It is to be noted that I am not going to keep issuing an On statement. As soon as it cuts On, the Action Status Bit will come On, and then the servo axis is in a controlled on state so it will maintain it’s position. Immediately after the Motion at Servo On state is done, the next step is to issue the axis to the next controlled state.

However, I would not want to do that until the Axis is truly on. So, I look at the Motion on the Servo Action Status of that axis.

Showing Why We Monitor Axis Tags For Instruction Control

In the previous images, I will cut the system On and go to a state of Two. After that, I will cut the system On at the Axis01.Servo Action Status. Once you do this, you will be able to see that the Motion at Servo On was issued a single time.

At this stage, the servo axis is active and monitoring position even when not moving. Now, if I cut off the system using the HMI_SystemOFF_PB, I would look at the Axis Servo Action Status as a reference to see if it is truly ON. In this case, if I use the Off button, this will get cut Off, but I would like to monitor that state in order to make sure that my servo is following the instructions.

Also, I would want to do it only once because in case I keep issuing it multiple times then you stand a greater chance of an instruction fault., which is not healthy for machine controls as you have to index it again to clear the error of the instruction.

Check out my Servo Motion Mastery course to get very detailed training and troubleshooting.

Click here to find out my about my servo courses.

This was a video to help you get a better idea and more profound insights into my preference of sequence. The use of Stops and other instructions are also self-explanatory. I do get a lot of questions and requests to justify the use of this sequence. In my eyes, this is a tried and true process that is not going to fail or fault out or even have instruction faults. It will also not try to falsely control something when it is not in a healthy state or in other words, a ready state.

Using the proper bits in the right spot is undoubtedly the correct function. A number of times people tend to ignore this and run into problems. You probably might have been into a code to see an instruction error out due to some reason. This is essential because of the lack of monitoring of the proper state of your Axis, motion Group, or Controller, can cause many different code errors or drive errors making it hard to troubleshoot.

The picture below shows an MAJ instruction in an error state as talked about….just an example.

These are a couple of foundational things that I abide by at Allen Bradley PLC Training. For instance, if we did aim Motion Axis Direct Command, the first thing we will do is to do an Off. We will first make sure it is Off. We will then make sure we fault Reset it to ensure that the system is cent percent healthy. After all this, we will do an On. As soon as it cuts On, we can do a JOG or MAM.

However, the first thing that we want to do is to make sure that we cut it Off, we Reset it, and then we cut it On. Thus, it would make no sense to ignore these when we do it naturally.

I have received this question on my E-mail and through a couple of other platforms that I have like my Patreon member’s area where I do more custom training based on member’s request. This is why I wanted everybody to have a good understanding of the procedure and of RSLogix 5000 Servo Control. You need to choose the correct bits and the correct actions to get a proper and healthy system in order to avoid unexpected faults.

My primary aim at Allen Bradley PLC Training is to teach people, bring value to them, and spread knowledge where I can.

Thanks,

Shane

RSlogix 5000 Servo – Proper Start Up Control 

Our goal is to provide to best education of controlling a servo and show the importance of the order of operation in which the RSLogix 5000 instructions should be programmed, this is hinted to many times by Rockwell in their software but unless you have experienced reasons why then it is not that obvious.

One hint would be if you have ever used the motion axis direct commands to control a servo for troubleshooting or testing. The control insists that we start, stop, reset in a certain order but don’t take those instructions I named literal, these are examples and are going to be talked about below to give you the best training for this.

Next hint that is known in the electrical industry can be compared to the same function of a frequency drive or VFD controls. Meaning, if you have ever had an issue where you commanded a start to a drive through programmed logic and seen that the VFD did not start then you may be aware of this reason. You cannot start a drive that has a start command held and a stop of some sort has not been cycled. A similar instance of this happen with abnormal events in a processor like a processor fault or a processor being swapped from remote run to program mode….just an example but there are many.

Abnormal process upsets happen in day to day operations of machines which can come from many different sources. Like any plc controls, Rockwell Automation controls are dependent on what hardware and software you are using the application so it is best to have a base understanding of your system. Ever component no matter who makes it stands a chance of process interrupts.

What I have done here in this article to help best illustrate this is to make a video which talks my best practices when it comes to servo controls and why, this video is a short but to the point to help save you time. If you have any questions then feel free to reach out to me.

In this video, I will justify why I use a specific sequence of operations and its benefits. I will also shed light on the reason why I use an “Off” at the beginning of the operation while using RSLogix 5000 Servo Control. I will take you through a detailed walkthrough of my preferred sequence and the advantages of using the same.

Instructing an Axis OFF in RSLogix 5000 or Studio 5000

In most of the systems that you come across in the industry, you will notice that the sequence starts with an “On” at the beginning. You will also come across the same sequence if you have been trained by Rockwell in some instances. with that being said, they do not cut the system Off before they do an On. However, as mentioned above, I have always chosen to issue an Off statement up-front because you are uninformed about the present state of the controller.

In the instance shown in the picture, the very first step of the state machine control is to make sure the servo is not faulted or the sercos ring then the motion group is synced and after all that has happened and the HMI_ServoSystem_ProcessStart is pressed then it instructs an MSF to make sure the servo is turned off before any other servo command is done. After the MSF instruction has finished and the Axis status is off then it will transition the state logic to 1.

For instance, there might be a situation where you could have lost communications with the controller due to an anomaly or any unprecedented situation. It is also not possible for you to know for sure whether the servo controller has not been told to run already or to cut on. It might have stayed in the on state for other controller or program reason as well, which you were unaware of. It is in opinion, it is crucial for you to cut it off in order to control it to limit the risk of entering into an uncontrolled state.

To put it in simpler terms, it is just like a drive holding an On bit, or a drive holding an Active bit at all times. Thus, it fails to run when you try to start it. Therefore, in order to avoid any instruction faults, it is imperative for you to cut it Off.

Making Sure The Servo Axis Does Not Have a Fault

Once that’s done, I go to the next part to control a Reset as shown in the image above. I always separate my Resets because in cases of faults or shutdowns, like a Motion System Shutdown, then the Shutdown status bit will come On thereby issuing the Shutdown Reset. However, if the Shutdown State is proper, and there is no Shutdown, but the Axis is faulted, I would only want to reset my Axis. Therefore, I am not performing both the actions in a single situation. I am only performing the one I need to.

Instructing the Servo Axis to Turn ON

In the picture above, if there is an instance where there is no Axis fault or a Shutdown Status, then I can either go immediately to a state where I can Home it if I wanted to, or I can cut the Servo On. In such a situation, I would first like to monitor the Bus of my Servo controller to ensure it is healthy.

I would then ensure that my Axis is not in a faulted state. I would, at this point turn the servo On. It is to be noted that I am not going to keep issuing an On statement. As soon as it cuts On, the Action Status Bit will come On, and then the servo axis is in a controlled on state so it will maintain it’s position. Immediately after the Motion at Servo On state is done, the next step is to issue the axis to the next controlled state. However, I would not want to do that until the Axis is truly on. So, I look at the Motion on the Servo Action Status of that axis.

Showing Why We Monitor Axis Tags For Instruction Control

In the previous images, I will cut the system On and go to a state of Two. After that, I will cut the system On at the Axis01.Servo Action Status. Once you do this, you will be able to see that the Motion at Servo On was issued a single time. At this stage, the servo axis is active and monitoring position even when not moving. Now, if I cut off the system using the HMI_SystemOFF_PB, I would look at the Axis Servo Action Status as a reference to see if it is truly ON. In this case, if I use the Off button, this will get cut Off, but I would like to monitor that state in order to make sure that my servo is following the instructions.

Also, I would want to do it only once because in case I keep issuing it multiple times then you stand a greater chance of an instruction fault., which is not healthy for machine controls as you have to index it again to clear the error of the instruction.

Check out my Servo Motion Mastery course to get very detailed training and troubleshooting.

Click here to find out my about my servo courses.

This was a video to help you get a better idea and more profound insights into my preference of sequence. The use of Stops and other instructions are also self-explanatory. I do get a lot of questions and requests to justify the use of this sequence. In my eyes, this is a tried and true process which is not going to fail or fault out or even have instruction faults. It will also not try to falsely control something when it is not in a healthy state or in other words, a ready state.

Using the proper bits in the right spot is undoubtedly the correct function. A number of times people tend to ignore this and run into problems. You probably might have been into a code to see an instruction error out due to some reason. This is essential because of the lack of monitoring of the proper state of your Axis, motion Group, or Controller, can cause many different code errors or drive errors making it hard to troubleshoot.

The picture below shows an MAJ instruction in an error state as talked about….just an example.

These are a couple of foundational things that I abide by at Allen Bradley PLC Training. For instance, if we did aim Motion Axis Direct Command, the first thing we will do is to do an Off. We will first make sure it if Off. We will then make sure we fault Reset it to ensure that the system is cent per cent healthy. After all this, we will do an On. As soon as it cuts On, we can do a JOG or MAM. However, the first thing that we want to do is to make sure that we cut it Off, we Reset it, and then we cut it On. Thus, it would make no sense to ignore these when we do it naturally.

I have received this question on my E-mail and through a couple of other platforms that I have like my Patreon member’s area where I do more custom training based on member’s request. This is why I wanted everybody to have a good understanding of the procedure and of RSLogix 5000 Servo Control. You need to choose the correct bits and the correct actions to get a proper and healthy system in order to avoid unexpected faults. My primary aim at Allen Bradley PLC Training is to teach people, bring value to them, and spread knowledge where I can.

So if you have any queries, you can reach out to me on YouTube, or on this website, or any other platforms like Patreon. I will be glad to help you. Thank you for your support.

Thanks,

Shane