Simple positioning with the PowerFlex 525 can add flexibility and functionality to your drive application without the need for additional PLC control. Use Connected Components Workbench to program your dive for limited logic control and unburden or back up your existing PLC.  The article below describes programming in detail.  Click Here for the manual section that describes the positioning function.   Click the thumbnail below for a YouTube video that offers a quick description of this feature:

About Positioning

The PowerFlex 525 can engage in simple positioning.  As stated in the drive manual:

The PowerFlex 525 drive includes a simple position regulator which can be used in a variety of position applications without the need for multiple limit switches or photo-eyes. This can be used as a stand-alone controller for simple applications (up to 8 positions) or in conjunction with a controller for more flexibility. 

Please note that this is not intended to replace high-end servo controllers or any application that needs high bandwidth or very high torque at low speeds. – 520-UM001

To put this in other words, the PowerFlex 525 can control system motion over specified distances using internal programming and digital inputs.   Positioning step-logic is distinct from velocity step logic in that the latter only allows motion over a specified time at a prescribed speed and cannot account for positioning requirements.

Positioning Quick Tips

Speed reference 1 must be set to positioning, with no exceptions.

You may set speed references 2 and 3 to your preferred sources and switch between the three as necessary, but to engage in a positioning function, speed ref 1 must be positioning.

You need an encoder for positioning.

An encoder has to be included for positioning.  Specifically, a quad or quad check encoder.  Single chan encoders are not recommended for positioning.

Note: Velocity steplogic, which is distinct from positioning in that it is based only on speed and time, can function with a single chan encoder, pulse train device, or no feedback at all.

Torque Preference Mode:  Vector.

If you are going to use an encoder and you want a high degree of accuracy, then a torque preference mode of Vector is recommended.  This selection provides more accurate speed feedback than does sensorless vector control and is designed for use with positioning.  With that said, you can use sensorless vector control with the positioning function.  

The Positioning Wizard

Here is a breakdown of the positioning wizard found in CCW:

Common Settings 1

Above is common settings page 1 for the positioning wizard.  Each selection field represents a parameter that may be set to aid in the positioning function of the PowerFlex 525.  Hover over a selection field with your mouse to see the parameter number in question.  To go over the items pointed out by blue arrows and red rectangles:

Within the Red Rectangle: These settings allow you to select the acceleration and deceleration time (1 and 2) and the maximum frequency.  You may set accel/decel up to 600 seconds and the frequency up to 500 Hz.

A: This is the selection field for speed reference 1.  As stated earlier, this must be set to positioning for a positioning function to be undertaken.

B: The reverse disable/enable function should be taken note of:  some processes can tolerate a reverse in direction and some cannot.  Take note and program accordingly.

C: Motor feedback type should be set to either quad or quad check if a positioning function is desired.

D: Up to two digital terminal blocks may be programmed to serve as logical inputs within a positioning function, allowing a positioning activity to work in conjunction with other functions within a process.

E: The relays and Opto-outputs for the PowerFlex 525 may be set to “StpLogic Out.”  This will cause these outputs to change states based upon the step that the logic sequence is currently within.  These outputs may also be set to respond to a number of other status conditions.  Take advantage of this as required to meet programming goals.

Common Settings 2

Common settings page 2 offers encoder settings and tuning options.  To, again, go over blue arrows and red rectangles:

A:  This field allows you to choose between the following options:

Time Steps:  Moves through the programmed positioning steps based only on the times programmed for each.  This mode does not require the use of an encoder, but does need the program to be set to absolute positioning and can only function in the forward direction.

Preset Input: With this mode, the steps programmed into the drive are triggered by digital inputs.  This allows a user to move between steps by simply engaging a digital input as desired.  This subprogram requires the drive to be set to absolute moves in the forward direction only.

Step Logic:  This is the actual positioning function with the PowerFlex 525.  The drive may move through all eight programmable steps or jump between them based on time, drive status, or the condition of digital inputs or network-based commands.  The drive may be set to either absolute or incremental moves and may travel forward or backward as needed.  This program must be coupled with a quad or quad check encoder.

Preset StpL:  This program functions identically to the Step Logic program with one difference:  the drive will jump to the step associated with a preset digital input upon starting motion.  This will only determine the first step of motion, however.  The steps after this will follow in order based on the programming of the drive.

StepLogic-Lst:  In this program, the drive will begin at the step it was at upon the last stop action taken.  the drive will then progress through each step as programmed.  this allows a drive to be stopped and then restarted without losing place within the step logic structure.

Within the Red Box: These five fields set encoder PPR, motor poles, home settings, and counts per unit.  The encoder PPR may be found on the datasheet for the encoder, or, you may take advantage of Rockwell’s recommendations for determining encoder PPR.  Motor pole count will be copied over from your startup settings with the default value being 4.  Find home direction and find home frequency set the motion direction and frequency when the drive is in a find home operation.  Counts per unit are where the fun begins:

Counts per unit is the number of points rotated through to represent one “unit” of motion.  What is a unit?  It’s up to you, one foot, one revolution, etc.  The current setup above shows 4096 counts per unit, so four revolutions per unit.  To let you know, the PF525 will accept a maximum number in Counts per Unit of 32,000.  Keep this value in mind if you are working with gearing: if your encoder counts per unit are 4096 and you are working with a 7:1 gearbox, then your ultimate counts per unit will be 28,672 (4096 x 7).  This limitation can be navigated by either putting the encoder on the output of the gearbox or by using a fractional input to the counts per unit field and then increasing the position input in the logic.

B: Tuning parameters help you set your drive for optimal performance.  Pos Reg Gain and Pos Reg Filter will adjust the position regulator filter and gain response.  If you are using sensorless vector control while positioning, the Ki and Kp speed loop will allow you to adjust the integral and proportional gain for a closed-loop system with an encoder.

Position Programming: Actions

Now we get into the actual programming of positions.  It is here that step logic shines, as a number of conditions and inputs can be used to program the progress from one position to another.  Once again, I have pointed out two functions with blue arrows that should pique your interest:

Within the Red Rectangle:  These three fields set the distance, time, and speed for the current step.  This means that if you set position to 25, the preset frequency to 10 Hz, and time to 10 seconds, then while within the current step, the drive will move toward a position 25 units ahead (or from home) at a speed of 10Hz and will do so within 10 seconds, or will stop moving after 10 seconds in any case.  By the way, the one “position unit” referred to is the counts per unit set up in common settings 2.

A:  This field sets whether the relays and Opto-outputs associated with step logic will change state when the step is completed.  This is a useful way for a drive to signal the completion of a step to associated equipment in a process.

B: This field determines whether the motion of the drive will be incremental or absolute.  Incremental moves are in the programmed direction over the distance programmed, without a reference to home.  This is great if your process needs only incremental moves of a certain distance at each step.  A selection of “absolute” causes the motion of each step to be in reference to a home position, meaning the position programmed into the step will now be considered a distance from the home reference.  Absolute moves shine when the items in motion need to be kept to a physical reference point for process needs.  

Position Programming: Logic

Within the Logic tab of a step, the fields inscribed in red appear.

Go To Next Step:  This field allows you to select what will prompt the 525 to move to the following step.  Digital inputs and time limits may be used to trigger a step-change, but you may also select “never, don’t step” to terminate a series of steps.

OR if/Then:  This allows you to engage in an “OR” logical relationship with your previously select step trigger.  This is valuable if you would like two different inputs to trigger a step-change in a process.  The “if ” portion provides the other side of the OR logical relationship with the initial trigger, and the “then” field allows you to choose an action which may be to move to a particular step or to end your step process.

About Homing

Positioning step-logic is capable of recognizing a “home” position for the system.  The home position is the “0” position to which all moves are in reference to when your “type of command” is set to absolute.  This is very useful if your process requires movement in reference to a fixed point or particular geometry.  If, however, you need simply to move forward across incremental steps, setting your step logic to “incremental” and foregoing a reference to home is possible.

Digital inputs can be used to set what this home position is:

Pos Redefine:  This digital input setting will allow you to use set (or reset) the home position to the current drive position by using a digital input.  Very useful to have as a fault or restart of your drive will require you to re-home.

Find Home: Activating this digital input will cause the drive to move from its current position to the home position.  It will move to the home position with the speed and direction set for find home in the “common settings 2” section of the set-up wizard.

Home limit: This digital input will indicate if the drive is in the home position.  Using this can allow you to take advantage of a photo-eye or a limit switch as a marker for the home position for your process.

For more information about drives and drive systems, check out the Variable Frequency Drive Main Help Page