Rotor Balancing

A Python package for static and dynamic rotor balancing calculations based on the methodology described in "Static and Dynamic Balancing using portable measuring equipment" by John Vaughan (Brüel & Kjær Application Note).

Features

• VibrationVector: Represents unbalance by means of a vector
• MassVector: Represents a mass placed at an angular position on a rotor
• StaticBalancing: Single-plane balancing for rotors
• DynamicBalancing: Two-plane balancing for rotors
• VibrationExtractor: Extracts vibration vectors from time-domain signals
• detect_rotation_freq: Detects rotation frequency from a trigger signal
• Four pluggable extraction methods: IQDemodulation (default), LeastSquaresFit, SynchronousAveraging, FFTExtraction

Installation

Install from PyPI:

pip install pyPRB

Or install from source:

git clone https://github.com/ladisk/pyPRB.git
cd pyPRB
pip install .

For development installation:

pip install -e .[dev]

Quick Start

Static Balancing Example

from pyPRB import VibrationVector, MassVector, StaticBalancing

# Initial measurements
V_0 = VibrationVector(amplitude=3.4, phase=116)  # No trial mass
V_1 = VibrationVector(amplitude=1.8, phase=42)   # With trial mass

# Trial mass: 2.0 g mounted at 0° on the rotor
trial_mass = MassVector(2.0, 0.0)

# Create balancer
balancer = StaticBalancing(V_0, V_1, trial_mass=trial_mass)

# Display measurement table
print(balancer)

# Compute compensation
comp_mass = balancer.compute_compensation()
# Output: Compensation mass: 2.01 g at position -30.8° on the rotor.

Dynamic Balancing Example

from pyPRB import VibrationVector, MassVector, DynamicBalancing

# Initial measurements (no trial masses)
V_1_0 = VibrationVector(7.2, 238)   # Plane 1
V_2_0 = VibrationVector(13.5, 296)  # Plane 2

# With trial mass in Plane 1
V_1_1 = VibrationVector(4.9, 114)   # Plane 1
V_2_1 = VibrationVector(9.2, 347)   # Plane 2

# With trial mass in Plane 2
V_1_2 = VibrationVector(4.0, 79)    # Plane 1
V_2_2 = VibrationVector(12.0, 292)  # Plane 2

# Trial masses: 2.5 g each, mounted at 0° on their respective planes
trial_mass_1 = MassVector(2.5, 0.0)
trial_mass_2 = MassVector(2.5, 0.0)

# Create balancer
balancer = DynamicBalancing(
    V_1_0, V_2_0, V_1_1, V_2_1, V_1_2, V_2_2,
    trial_mass_1=trial_mass_1, trial_mass_2=trial_mass_2
)

# Display measurement table
print(balancer)

# Compute compensations for both planes
comp_mass_1, comp_mass_2 = balancer.compute_compensation()
# Output:
# +---------+---------------------+------------+
# |  Plane  |  Compensation Mass  |  Position  |
# +=========+=====================+============+
# |    1    |       2.95 g        |   50.2°    |
# +---------+---------------------+------------+
# |    2    |       2.84 g        |   -81.9°   |
# +---------+---------------------+------------+

Extracting Vibration Vectors from Measurements

import numpy as np
from pyPRB import (
    VibrationExtractor, detect_rotation_freq,
    MassVector, StaticBalancing,
)

# Synthetic signals (B&K Example 2)
sample_rate = 10000  # Hz
f0_true = 25.0       # rotation frequency (Hz)
duration = 5.0       # s
t = np.arange(0, duration, 1 / sample_rate)
rng = np.random.default_rng(0)

trigger = np.sign(np.sin(2 * np.pi * f0_true * t))
signal_run0 = (3.4 * np.cos(2 * np.pi * f0_true * t + np.deg2rad(116))
               + 0.05 * rng.standard_normal(len(t)))
signal_run1 = (1.8 * np.cos(2 * np.pi * f0_true * t + np.deg2rad(42))
               + 0.05 * rng.standard_normal(len(t)))

# 1. Detect rotation frequency from the trigger signal
f0 = detect_rotation_freq(trigger, sample_rate=sample_rate, max_freq=50.0)

# 2. Create extractor (default method: IQ demodulation)
extractor = VibrationExtractor(sample_rate=sample_rate, rotation_freq=f0)

# 3. Extract vibration vectors for each measurement run
V_0 = extractor.get_vibration_vector(signal_run0, trigger)
V_1 = extractor.get_vibration_vector(signal_run1, trigger)

# 4. Use the vectors for balancing
trial_mass = MassVector(2.0, 0.0)
balancer = StaticBalancing(V_0, V_1, trial_mass=trial_mass)
comp_mass = balancer.compute_compensation()
# Output: Compensation mass: 2.01 g at position -30.8° on the rotor.

Balancing procedure

Static Balancing

For a rotor with unbalance in a single plane:

1. Measure initial vibration vector V₀
2. Add known trial mass m and measure resulting vibration V₁
3. Compute compensation mass with StaticBalancing

Dynamic Balancing

For a rotor requiring two-plane balancing:

1. Measure initial vibration vectors in both planes: V₁,₀ and V₂,₀
2. Add trial mass m₁,₁ in plane 1, measure: V₁,₁ and V₂,₁
3. Add trial mass m₂,₂ in plane 2, measure: V₁,₂ and V₂,₂
4. Compute compensation masses in both planes with DynamicBalancing