Servo Homing Part 1 - LS Electric L7C & L7P Servo System at AutomationDirect

For this homing tutorial, we’re going to use the exact same hardware as we used in the quick start video. The only difference is the Servo motor is now coupled to a linear slide with three proximity sensors to give us the over-travel limits and a home signal, which I wired to these pins on the I/O connector. You would normally wire a homing start signal from your controller to a digital input to initiate homing. Or you could also send a command via coms to start homing. I didn’t do either of those here because we’re going to control homing from the drive configuration software. Could I have made this the positive limit? Sure! It just has to align with however you set up your directions in the drive configuration. So let’s do that. In the drive configuration software – which you can download for free from AutomationDirect.com – I’ll select the drive I am using and hit the connect button. I see the drive information pop up over here and this green blinky light down here so I know I am connected. Let’s go to setup, and return to factory setting so you know exactly where I am starting from. Yes, we want to do that. Give it a couple seconds. Let’s also reset the drive’s controller to ensure we have a good clean start. Yes we want to do that. Wait for it to reconnect and we are good to go. Bring up the setup wizard. Go online. Yes, we want to read the parameters from the drive so when we write out the new ones we don’t overwrite the drive with whatever this configuration software's default values were. We want to set up the encoder for auto, and we want to be in index mode. Homing doesn’t make sense in velocity or torque modes and homing is handled by your controller in pulse mode. You could use homing in the mode where you start in index mode and then go to pulse mode. This next screen is fine. This rotation dialog is the key to getting homing to work because it defines the positive direction. Right now it says a positive command will turn the shaft counterclockwise. If I reach over and rotate our slides screw counterclockwise, we see the carriage moves this way. So this is the “positive” direction and this will need to be set up as the positive limit switch in the digital I/O dialog when we get to it. If we switch this, then a positive movement generates a clockwise rotation of the screw, which is this way, and we would have to define this guy as the positive limit in the digital I/O dialog. That’s really important – your limit switches and direction definition have to be aligned or homing won’t work. For us, we’ll use this default direction which again, makes this the positive direction so this guy will need to be the positive limit. For this demo, we aren’t concerned with ESTOP or braking so I’ll skip through that stuff. I’ll select the internal torque limit which is currently set to 300%. That’s so the drive will limit how much torque can be applied if you slam the carriage into one of the end stops, a foreign object gets bound up in the power transmission, or If the material or product you are moving gets caught or stuck on something during the move. And normally, you will want to set to something gentle like a 25 or 30 percent torque limit when you first start out just in case something goes wrong. We’re not using the position signals, so we can skip that. Digital inputs. We’re not using a servo on signal because we’ll control that from the software. We wired the home signal to Input 2 and it’s NPN. We’re not using these. We wired the over travel sensors to the default inputs seven and eight and in particular, we need Pin 7 to be the positive over travel limit and Pin 8 to be the negative limit to align with the direction we set up earlier. Those are also NPN. Limit and home switches should always be normally closed, that way if you get a break in the wire the machine won’t run until you fix it. We aren’t going to use the emergency stop in our demo where the shaft isn’t really coupled to anything, but you will definitely want to add it and test it for use in your system. And we’re not going to use this either. Outputs: I’ll turn all of these off except the origin signal. That tells us when homing thinks it’s done. This is where you select the homing method. We’re going to skip this page because we are going to use this button up here to bring up this side menu where we can do the same configuration stuff and test homing at the same time. It even has this little reference diagram. Unfortunately, these descriptions don’t show up over here, so I’m going to grab a screen shot of the descriptions, so we have them handy later. And we’re done! Make sure the drive is disabled, and write the configuration to the drive. Wait for the confirmation ... there it is. Normally I would save it to file, but we haven’t set up the homing yet, so I’ll wait on that. And don’t forget to do a soft reset of the controller after a write to ensure it has a fresh start with the new parameters. Wait for it to reconnect. Got it. Some parameters, like a mode change require a soft reset. We make it a point to highlight the parameters that require a soft reset when we come across them in all the videos. In the setup wizard, the online button is dimmed. That happens sometimes, so I’m gonna click away on several of these tabs just to force the screen to refresh when I come back to the wizard. Now we can get back online with the drive. And yep, we want to read the drive parameters. Before doing homing, let’s check everything out. First, let’s test our sensors. Bring up the inputs dialog. If I hold a screw driver over what I think the positive limit should be – yep the positive limit lit up. Negative limit? Yep. And home sensor. Perfect. This carriage has two detection points which are also called flags, pawls, tags, etc., which means the home position will change depending on what we’re doing and which of these hits the sensor first. Now let’s go to jog. Change the speed to something slow. How about 120 revolutions per minute or two revs per second. Don’t forget to hit enter to get the red number to take. Enable the drive's output. If I hold down the positive direction, yep the carriage goes to the left towards the positive over travel limit. Negative direction, and it goes towards the negative over travel limit. Perfect, exactly what we wanted. Everything seems to be working as expected, so now we just click on this guy to bring up the homing dialog where we can configure and test homing. Join me in Part 2 where we’ll walk through all the various homing options and demonstrate them on this linear slide. Meanwhile, click here to learn more about the LS Electric L7C Servo System. 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