Spindle Measurement

Spindle Error Analyzer: Tests Performed

The Spindle Error Analyzer runs all the necessary tests of spindle motion to help predict and document performance issues related to part quality including tests specified in ANSI, ISO, JIS international standards.

The following tests and utilities are available in SEA and are detailed below:

Rotating Sensitive Radial

radial-rotating sensitive direction plot


Rotating Sensitive Radial acquires distance data from two probes positioned 90° apart. The probes measure the X and Y displacement of the axis of rotation to generate a polar plot using the Tlusty or B89.3.4 method. This test is valid for processes such as milling, boring, and drilling, where the tool is rotating in the spindle.
Rotating Sensitive Radial measures changes in the position of the axis of rotation in two directions and evaluates the following aspects of machine tool performance:

Performance Parameter

Related Source Problems

Roundness capability due to synchronous spindle error motion Out of round bearing races
Out of round bearing seats
Misaligned bearing seats
Surface finish capability due to asynchronous spindle error motion Bearing wear
Improper preload
Structural vibration
Performance degradation at specific speeds Inadequate stiffness
Imbalance
Resonant frequencies of machine

 

Data Collected

Calculated Values

X and Y (Two Probes) TIR X, TIR Y
Total Error
Asynchronous Error
Synchronous Error
RPM

 

Fixed Sensitive Radial

radial-fixed sensitive direction plot

Fixed Sensitive Radial acquires displacement in the X direction relative to angular position of the axis of rotation and displays the data in a polar plot.
This test is valid for processes such as turning and some grinding processes where the part is rotating in the spindle, or where the point of contact between the grinding wheel and part are at a fixed position such as surface grinding.

It measures changes in the axis of rotation in one direction and evaluates the following aspects of machine tool performance:

 

Performance Parameter

Related Source Problems

Roundness capability due to synchronous spindle error motion Out of round bearing races
Out of round bearing seats
Misaligned bearing seats
Surface finish capability due to asynchronous spindle error motion Bearing wear
Improper preload
Structural vibration
Performance degradation at specific speeds Inadequate stiffness
Imbalance
Resonant frequencies of machine

 

Data Collected

Calculated Values

X (One Probes) TIR X, TIR Y
Total Error
Asynchronous Error
Synchronous Error
RPM

 

Tilt - Fixed Sensitive Radial

tilt-fixed sensitive direction plot

Tilt-Fixed Sensitive Radial measures variations in the tilt of the spindle during rotation. Data is collected from either the X, X2 or Y, Y2 probe pair. Using the readings from each probe and the distance between the probes, the tilt of the spindle is calculated at each angular location measured. The results are reported in µradians.

It evaluates the following aspects of machine tool performance and their degradation as distance from the spindle is increased:

Performance Parameter

Related Source Problems

Roundness capability due to synchronous spindle error motion Out of round bearing races
Out of round bearing seats
Misaligned bearing seats
Surface finish capability due to asynchronous spindle error motion Bearing wear
Improper preload
Structural vibration
Performance degradation at specific speeds Inadequate stiffness
Imbalance
Resonant frequencies of machine

 

Data Collected

Calculated Values

X, X2 or Y, Y2 (Two Probes) Total Error
Asynchronous Error
Synchronous Error
RPM

Axial Error Motion

axial error motion plot

Axial Error Motion acquires distance data from one probe in the Z axis (typically channel 3). The probe measures the axial motion of the spindle. Angular position data is also required and is obtained from the eccentricity motion measured by another probe in the X or Y axes or an index or encoder signal. It measures changes along the axis line and evaluates the following aspects of machine tool performance:

Performance Parameter

Related Source Problems

Surface finish capability Bearing wear
Improper preload
Structural vibration
Performance degradation at specific speeds Inadequate stiffness
Imbalance
Resonant frequencies of machine

 

Data Collected

Calculated Values

Z (One Probe) Fundamental
Residual Error
Total Error
Asynchronous Error
RPM

 

FFT

fft plot of spindle error motion


The FFT analysis test acquires sampled amplitude data from a single probe in the time domain and converts the data into the frequency domain. A graph of amplitude vs. frequency is produced. The graph is updated once per second, showing the FFT results on the most recent data set. FFT data is used in identifying bearing frequency, adjacent machinery frequencies and the like.

Can be used with live measurement data for a rotating spindle, or can capture events such as a "ping" test when the machine is struck with a plastic hammer. Graph includes these features:

  • Display of cursor selected FFT value
  • View manually selected portion of horizontal (frequency) scale
  • View manually selected portion of vertical (displacement) scale
  • Ping: View live data and trigger level before freezing

Data Collected

Calculated Values

Any Axis (One Probe) Primary Frequencies
Bearing Frequencies
Orders
RPM

 

Target Reversal (Donaldson Reversal)

target reversal display spindle error motion

 

Target Reversal allows data from two test runs to be combined in such a way that form/shape errors in the target are separated from the synchronous error motion of the spindle.

The function generates two sets of measurements of the spindle. The first is a standard fixed radial measurement. The second will have exactly the same data from the target, but an equal and opposite set of data from the spindle. When the two sets of data are combined, the form error of the target is separated from the synchronous error motion of the spindle.

Target Reversal works only with Fixed Radial tests.

 

Shift vs. RPM

spindle thermal stability

 

RPM-based changes in spindle position/performance

As a spindle turns at different speeds, its dynamic characteristics change. Shift vs. RPM charts axis position shift in up to five axes plus tilt measurements in two axes at different spindle speeds. The graph changes plot-line thickness as RPM is decreased making increase/decrease variations visible.

Thermal Stability

spindle thermal stability

Changes from Machine Generated Heat

Stability tests measure the effects of heat produced by the spindle itself during operation. These tests are performed while the spindle is rotating. Because they are designed to test for self-generated heat they are of a relatively short duration. Sixty minutes is typical. Results are charted with temperature data when available. No measurement is made of rotational error motions, only the average movement of the center of the target is charted.

These tests measure the ability of the machine to maintain the relative position between the tool and workpiece and evaluate the following aspects of machine tool performance:

  • Locate features on a part at any distance from the spindle face
  • Location of a hole
  • Depth of a hole
  • Location of a contour
  • Isolate problems of simple X and Y motion from more complex angular motions

3 Probe Stability

Three probe stability tests simply chart the movement of the target in the X, Y, and Z axes.

5 Probe Stability (Tilt)

Five probe thermal stability is essentially the same as the three probe stability test but there is an additional probe in the X and Y axes. Using the data from these additional probes the change in the tilt of the spindle can be charted as a function of time and temperature. This is important in applications where machining takes place at various distances from the spindle face. By measuring the tilt angle of the spindle, it is possible to calculate the tool position at any axial distance from the spindle face.

Additional Features

  • Editable labels on temperature curves (i.e. Ambient, Frame etc.)
  • Open and shorted temperature probe alert
  • Manual scale adjustment

 

ETVE (Environmental Temperature Variation Error)

spindle thermal stability

Ambient Temperature Changes

This tests for movement in the spindle relative to the mounting system due to ambient temperature changes. This test is performed without spindle rotation and with power to the machine turned off. Because of the slow changing nature of ambient temperature and the time required for the thermal mass of a machine tool to "soak out" to the ambient temperature, these tests are of long duration with twenty-four hours being typical. This measurement is performed with a probe in the X, Y, and Z axes.

The change in each axis over time is plotted with temperature information from the temperature sensors if used.

Additional Features

  • Editable labels on temperature curves (i.e. Ambient, Frame etc.)
  • Open and shorted temperature probe alert
  • Manual scale adjustment

Oscilloscope

oscilloscope

 

The Oscilloscope is a utility display that emulates a basic oscilloscope, allowing a time based view of the data acquired on any of the five probe channels. The default data selection choice shows the data from the selected revolutions with the zero offset (DC component) removed. An alternate selection on the VIEW menu shows a longer time sample of data with the DC component intact.

Probe Meter

probe meter

 

The Probe Meter indicates the current probe/target gap for the selected probe. The meter is an aid during setup when the probes are positioned in the probe mounts, and a visual indication of low frequency vibration or spindle deflection from mechanical shock elsewhere on the machine.

 

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