Why use a Polynomial-Fit FB?

It is often the case that your 'motion-design' is given to a 'Tool-Part'. Then, you add more Parts and join other Parts to the Tool-Part to create a more complex kinematic-chain.

A different Part, with a different motion to the Tool-Part, is driven. This is normal inverse-kinematics.

If you want to drive the Part with a servo-motor, you can use a Measurement FB and a Graph FB, and can give a servo-controller the required motion of a servo-motor as a series of data-points.

While this is often satisfactory, it is often preferable to give the servo-controller a series of polynomials rather than a series of a data-points.

The output from the Poly-Fit FB is the 'best-fit' motion of the input, but defined as a series of one or more 5th order Polynomials. You can save the output of the 'best-fit':

as 'motion-values' at its output-connector
to a CSV file,
in the format required for a Schneider Electric [Elau] servo-controller.

Note: The Poly-Fit FB uses all three data-channels to find the 'Best-Fit' to the data at its input-connector.

Polynomial FB

Add Polynomial-Fit FB

Modelling FB toolbar > Polynomial-Fit FB [Above Graphic-Area]


Add menu > Add Polynomial-Fit  FB


Polynomial Fit dialog-box





STEP 1: Add the Polynomial=Fit FB to the graphic-area

1.Click Modelling FB Toolbar > Add Polynomial Fit FB
2.Click again in the graphic-area to 'place' the Polynomial-Fit FB.

The Polynomial Fit FB is now in the graphic-area.

STEP 2:  Connect a wire to its input-connector

Each wire you connect to the Polynomial-Fit FB usually has three data channels with three derivatives of motion-values. See Data-Channels.

1.Add a Measurement FB to measure the linear or angular dimension you want to control with a Servo-motor
2.Connect a wire from the Measurement FB to the Polynomial Fit FB

STEP 3: Open the Polynomial-Fit FB dialog-box:

1.Double-click a Polynomial-Fit FB in the graphic-area


Polynomial Fit dialog-box

Motion Function-Blocks separator

The Poly-Fit FB can use the X-axis values of Blend-Points in a related motion to give the same timing of the 'Best-Fit' polynomials.

1.Click the 'Padlock' to unlock the box.
2.Click a Motion FB.

The name of the Motion FB is now in the 'list box'.

3.Click the padlock again to make sure you do not accidentally add another Motion FB to the list.


1.Edit Parameters, as required, to minimize error between the Best-Fit and the Measured data.

The algorithms fit a series of concatenated polynomials to the motion data that is at the input-connector.

See Poly-Fit dialog


Save the polynomial data to disk.


Tutorial and Reference Help Files for MechDesigner and MotionDesigner 13.2 + © Machine, Mechanism, Motion and Cam Design Software by PSMotion Ltd