Ellipse 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 whole 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 elliptical helical or three-dimensional linear profiles in this example we will use a two-axis elliptical interpolation to draw an ellipse we will be using an xpm Elin ellipse interpolation function block for our move today the interpolation movement is defined as a circular interpolation in the position data table in the xgp software the xpm Elin function block then modifies the movement into an ellipse when calculating the motion paths 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 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 an elliptical interpolation so we see that if the axes are ready and homed and we make the Run lips interpolation bit true we will execute motion manager State 40 starting with line 374 of the code we see that motion states 40 41 and 42 are all execution of direct start commands to position the three axes for the start of the elliptical interpolation in Motion state 40 the z-axis raises the pen off the paper then goes to Motion state 41 State 41 moves the X and Y axes to the starting position of 0 0 and moves to State 42 State 42 moves the z-axis down until the pen is touching the paper again the final function in Motion state 42 is to move to State 43 which is the actual execution of the elliptical interpolation we see in state 43 that it will make axis one command. ellipse interpolation start 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. ellipse interpolation start is used in three places the first one is the spot in the interpolation routines program that we already looked at the next two are both in the 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 both instances of this bit are on line 159 if we scroll down to that line we see that if the bit goes High and the axis is ready the PLC will execute an ellipse interpolation it selects axis one for this move and it will execute step number 30 in the axis one position data table it will also have a ratio of 5,000 and a degree of 3600 the ratio is the position relationship between the Master axis and the sub axis for step 30 data a value of % would be a perfect circle a ratio of 50% would put the sub axis outermost point at 1/2 of the Master axis position value a ratio of 150% would put the sub axis at 1 and 1/2 times the position of the Master axis the unit for the ratio is in hundreds of a percent so a value of 5,000 would be 50.00% degree is the angle the ellipse starts at based on the parent Circle construct it is in t of a degree so 3600 is 360. finally we see that the bit will be reset once the xpm Elin Don 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 30 let's take a look at the position data table for axis 1 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 AIS 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 position data this will open the one AIS position data table we scroll down to step 30 and see that it is an incremental circular interpolated move we also see that it is a single-end move so step 30 will execute once and then stop finally the sub AIS for the move is set to axis 2 to properly understand interpolated moves it is necessary to view the position data tables for all axes we will use since step 30's interpolation sub axis is Axis 2 let's open the access to position data table as well to see both position data tables at the same time we go to window tile horizontally this aligns the axis 2 position data above the axis one position data it is important to note that axis one is our xaxis and axis 2 is our y AIS in X GPM 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 30 of AIS one position data table the system will also execute line 30 of axis 2 position data table as AIS 2 is listed as the sub axis for the axis one move let's scroll down and take a look at line 30 of the axis 2 position data table in this case the only fields that matter for our interpolation are the target position field and the circular interpolation auxiliary point and circular interpolation mode Fields the software ignores the other entries as this is the sub axis now that we have 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 the x-axis at zero and the y- AIS at zero prior to triggering the ellipse interpolation line 30 will execute a circular line from the starting point to the Target position in both axes so our Circle will start at position 0 0 and end at position 0 since the start and end positions are the same the Circle will begin and end at the same spot the system will set a center point for this circle at 1,00 1,000 and only run a single Transit since our circular interpolation turns column is zero we selected the center point based on our application all of these values will be application specific depending on what you're trying to accomplish with your move the xpm Elin function block will then modify this circle into an ellipse using the ratio and degree information we looked at earlier this information is enough for the motion controller to calculate exactly how many pulses to send to each axis 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 the 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 from for more detail we want a smooth profile that ends at the specified Point simultaneously for both axes so we will leave this setting at synth let's watch our motion system as we trigger an ellipse interpolation we see the system draw a single ellipse that stopped exactly where it started perfect this function block is very flexible we could leave the position data table information alone and just change the ratio and degree values to create all sorts of ellipses with the same start stop and around the same center point we could also alter the position data table to change what type of ellipse is drawn where it is drawn on the paper and much more we have now successfully created an ellipse using the xpm Elin function block for the xgb plc