Linear Interpolation - LS Electric XGB PLC from AutomationDirect

let's look at a motion application with the ls electric xgb PLC for this example we will be using a 3axis motion system which utilizes many components offered at automationdirect.com our system is built on a sure frame extruded aluminum base with casters it utilizes igus dryin actuators and sure motion couplers from automation direct attached to LS electric gearboxes driven by l7p Servo drives and Motors these drives are controlled by P Trin outputs from an xem dn32 HP 6axis motion controller we have attached a mounting plate and Pen to allow us to trace the profile we will be working on today interpolated motion can be used to move in fairly simple two-dimensional linear patterns such as angular lines or more complex two or even three-dimensional patterns such as a circular helical or three-dimension linear profile in this example we will use a two-axis linear interpolation to draw a triangle we will be using the xpm IST indirect start function block for our move today this function block is covered in more detail in The Help topic on the indirect start and its uses in xg5000 the function block uses the position data table in the X GPM software to predefine our linear interpolation we have the XM motion demo project file open in xg5000 have connected with the XM CPU and are in monitor mode this file is available to download load from the xgb interactive guide at automationdirect.com let's open the interpolation routines structured text program and go to line 43 of the code here we find the trigger Logic for the various interpolation routines this program has been set up to use the user variable motion manager State as the index for a state machine we are doing a linear interpolation so we see that if the axes are ready and homed and we make the Run linear interpolation bit true we will execute motion manager State 10 starting with line 76 of the code we see that motion states 10 11 and 12 are all execution of direct start commands to position the three axes for the start of the linear interpolation the z-axis in this case is positioned so that the pen is touching the paper and the X and Y axis are both positioned at 200 pulses the final function in Motion state 12 is to move to State 13 which is the actual execution of the linear interpolation we see in state 13 that it will make axis one command. linear interpolation move true Let's Run a search to find this bit elsewhere in the logic we can rightclick on the bit and go to find replace find text this opens the find replace popup window let's set the lookin box to multiple windows and then select select all from the find what drop down window it already put the variable name into the search box and we can now click find all it doesn't appear that anything happened but if we look at the information window in the lower right corner of the screen we see that the find one tab has automatically been selected let's expand that window upwards and here we see the results of our search we see that axis one command. linear interpolation move is used in four places the first one is the spot in the interpolation routines program that we already looked at the next three are all in axis one motion program so let's take a look at them we go to the project window on the left side of the screen maximize the axis one motion program heading and double click on program the first entry is on line 132 and we see that if this bit goes High the PLC will copy a 10 into the variable indirect step number if we now look at line 151 we see that a positive transition or Rising Edge one-hot instruction will activate the indirect start function block we set the indirect step number to 10 earlier so this is the line in the position data table for axis one that will be executed for a linear interpolation finally we see that the bit will be reset once the indirect start done output goes high this occurs as soon as the move is started so it should not be used as an indicator of motion completion to further dive into the details of Step number 10 let's look at the position data table for axis one in X GPM to open X GPM from the xg5000 software we go to tools position control this will open the xgp software we can then open the XM motion Demo X GPM file we will connect with the controller in X GPM as well we have already configured access one and access 2 parameters in The Help topic on initial motion configuration please refer to it for more details to open the position data table we will go to the project window on the left side of the screen and maximize number one access data we can then double click on position data this will open the one AIS position data table we scroll down to line 10 and see that it is an absolute linear interpolated move and the sub axis for the move is set to axis 2 to properly understand the interpolated moves it is necessary to view the position data tables for all axes we will use since the linear interpolation sub axis is Axis 2 let's open the axis 2 position data table as well to see both position data tables at the same time we go to window tile horizontally this aligns the axxis 2 position data above the axis one position data table it is important to note that axis one is our x-axis and axis 2 is our y- AIS looking at lines 10 through 12 of the axis one position data table we see three absolute linear interpolation moves the first two are single moves that continue to the next move and the third in the sequence is a single move that ends upon completion if we look at each of these moves we see that axis 2 is selected as the sub axis NX gpn M when a particular line of the table calls out a sub axis for the move the corresponding line in the sub axis position data table is what is executed as part of the interpolation in our case when we call line 10 of Access One position data table the system will also execute line 10 of access 2 position data table since axis 2 is listed as the sub axis for the axis one move since we are looking at lines 10 through 12 of axis one and each lists axis 2 as the sub axis let's look at lines 10 through 12 of the axis 2 position data table as as well we see that these three moves are all absolute single axis moves they do not need to be set as interpolated moves since the main axis step calls out the control type of the sub axis now that we've looked at the mechanics of how the multi-axis information is interpreted let's look at the positions and velocities of the moves themselves remember that our program positions each of the axes at position 200 prior to triggering the indirect start for the interpolation line 10 will be an x-axis move to a position of 2500 and a y- axis move to a position of, 1600 line 11 will move the x-axis back to position 200 while the y- AIS goes to 3200 and then the final move line 12 will keep the x-axis at 200 and only move the y- axis back to 200 this will lead to the system ending exactly where it started it is important to note that with interpolation the system uses the sub axis position but ignores the sub axis speed setting instead it uses the parameter setting for interpolation speed and some advanced math functions to calculate the axis speed of each axis for this move if we go to the parameter window we can see this is set to synth the documentation goes into detail on how it calculates these speeds so please refer to it for more detail we want a smooth profile that ends the specified Point simultaneously for both axes so we will leave this setting at synth let's watch our motion system as we trigger a linear interpolation we see the X and Y axis start drawing then when they reach the preset positions automatically move to the second segment of the move and finally end with just the y- AIS moving the pen back to the starting point just what we expected perfect we have now executed a series of linear interpolations to create a basic pattern this system is very flexible and can have many sequential steps so all sorts of interesting patterns and functions are possible with linear interpolation using the xgb plc