Balancing Machine
Encyclopedia
A balancing machine is a measuring tool used for balancing rotating machine parts such as rotors for electric motor
s, fans
, turbine
s, disc brake
s, disc drive
s, propeller
s and pump
s. The machine usually consists of two rigid pedestals, with suspension and bearing
s on top supporting a mounting platform. The unit under test is bolted to the platform and is rotated either with a belt-, air-, or end-drive. As the part is rotated, the vibration
in the suspension is detected with sensors and that information is used to determine the amount of unbalance in the part. Along with phase information, the machine can determine how much and where to add weights to balance the part.
In a hard-bearing machine, balancing is done at a frequency lower than the resonance frequency
of the suspension. In a soft-bearing machine, balancing is done at a frequency higher than the resonance frequency of the suspension. Both types of machines have various advantages and disadvantages. A hard-bearing machine is generally more versatile and can handle pieces with greatly varying weights, because hard-bearing machines are measuring centrifugal effects and require only a one-time calibration. Only five geometric dimensions need to be fed into the measuring unit and the machine is ready for use. Therefore, it works very well for low- and middle-size volume production and in repair workshops.
A soft-bearing machine is not so versatile with respect to amount of rotor weight to be balanced. The preparation of a soft-bearing machine for individual rotor types is more time consuming, because it needs to be calibrated for different part types. It is very suitable for high-production volume and high-precision balancing tasks.
Hard- and soft-bearing machines can be automated to remove weight automatically, such as by drilling or milling, but hard-bearing machines are more robust and reliable. Both machine principles can be integrated into a production line
and loaded by a robot arm or gantry, requiring very little human control.
s, which measure acceleration of the vibration, can also be used.
A photocell (sometimes called a phaser), proximity sensor
, or encoder is used to determine the rotational speed, as well as the relative phase of the rotating part. This phase information is then used to filter the vibration information to determine the amount of movement, or force, in one rotation of the part. Also, the time difference between the phase and the vibration peak gives the angle at which the unbalance exists. Amount of unbalance and angle of unbalance give an unbalance vector.
Calibration is performed by adding a known weight at a known angle. In a soft-bearing machine, trial weights must be added in correction planes for each part. This is because the location of the correction planes along the rotational axis is unknown, and therefore it is unknown how much a given amount of weight will affect the balance. By using trial weights, you are adding a known weight at a known angle and getting the unbalance vector caused by it. This vector is then compared to the original unbalance vector to find the resultant vector, which gives the weight and angles needed to bring the part into balance. In a hard-bearing machine, the location of the correction plane must be given in advance so that the machine always knows how much a given amount of weight will affect the balance.
A blade balancing machine attempts to balance a part in assembly, so minimal correction is required later on. Blade balancers are used on parts such as fans, propellers, and turbines. On a blade balancer, each blade to be assembled is weighed and its weight entered into a balancing software package. The software then sorts the blades and attempts to find the blade arrangement with the least amount of unbalance.
Portable balancing machines are used to balance parts that cannot be taken apart and put on a balancing machine, usually parts that are currently in operation such as turbines, pumps, and motors. Portable balancers come with displacement sensors, such as accelerometers, and a photocell, which are then mounted to the pedestals or enclosure of the running part. Based on the vibrations detected, they calculate the part's unbalance. Many times these devices contain a spectrum analyzer
so the part condition can be monitored without the use of a photocell and non-rotational vibration can be analyzed.
Electric motor
An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...
s, fans
Fan (mechanical)
A mechanical fan is a machine used to create flow within a fluid, typically a gas such as air.A fan consists of a rotating arrangement of vanes or blades which act on the air. Usually, it is contained within some form of housing or case. This may direct the airflow or increase safety by preventing...
, turbine
Turbine
A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...
s, disc brake
Disc brake
The disc brake or disk brake is a device for slowing or stopping the rotation of a wheel while it is in motion.A brake disc is usually made of cast iron, but may in some cases be made of composites such as reinforced carbon–carbon or ceramic matrix composites. This is connected to the wheel and/or...
s, disc drive
Disc Drive
Disc Drive or Disc drive might refer to:* Disk drive is a form of data storage for computers* DiscDrive was the afternoon show on CBC Radio 2...
s, propeller
Propeller
A propeller is a type of fan that transmits power by converting rotational motion into thrust. A pressure difference is produced between the forward and rear surfaces of the airfoil-shaped blade, and a fluid is accelerated behind the blade. Propeller dynamics can be modeled by both Bernoulli's...
s and pump
Pump
A pump is a device used to move fluids, such as liquids, gases or slurries.A pump displaces a volume by physical or mechanical action. Pumps fall into three major groups: direct lift, displacement, and gravity pumps...
s. The machine usually consists of two rigid pedestals, with suspension and bearing
Bearing (mechanical)
A bearing is a device to allow constrained relative motion between two or more parts, typically rotation or linear movement. Bearings may be classified broadly according to the motions they allow and according to their principle of operation as well as by the directions of applied loads they can...
s on top supporting a mounting platform. The unit under test is bolted to the platform and is rotated either with a belt-, air-, or end-drive. As the part is rotated, the vibration
Vibration
Vibration refers to mechanical oscillations about an equilibrium point. The oscillations may be periodic such as the motion of a pendulum or random such as the movement of a tire on a gravel road.Vibration is occasionally "desirable"...
in the suspension is detected with sensors and that information is used to determine the amount of unbalance in the part. Along with phase information, the machine can determine how much and where to add weights to balance the part.
Hard-bearing vs. soft-bearing
There are two main types of balancing machines, hard-bearing and soft-bearing. The difference between them, however, is in the suspension and not the bearings.In a hard-bearing machine, balancing is done at a frequency lower than the resonance frequency
Resonance
In physics, resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. These are known as the system's resonant frequencies...
of the suspension. In a soft-bearing machine, balancing is done at a frequency higher than the resonance frequency of the suspension. Both types of machines have various advantages and disadvantages. A hard-bearing machine is generally more versatile and can handle pieces with greatly varying weights, because hard-bearing machines are measuring centrifugal effects and require only a one-time calibration. Only five geometric dimensions need to be fed into the measuring unit and the machine is ready for use. Therefore, it works very well for low- and middle-size volume production and in repair workshops.
A soft-bearing machine is not so versatile with respect to amount of rotor weight to be balanced. The preparation of a soft-bearing machine for individual rotor types is more time consuming, because it needs to be calibrated for different part types. It is very suitable for high-production volume and high-precision balancing tasks.
Hard- and soft-bearing machines can be automated to remove weight automatically, such as by drilling or milling, but hard-bearing machines are more robust and reliable. Both machine principles can be integrated into a production line
Production line
A production line is a set of sequential operations established in a factory whereby materials are put through a refining process to produce an end-product that is suitable for onward consumption; or components are assembled to make a finished article....
and loaded by a robot arm or gantry, requiring very little human control.
How it works
With the rotating part resting on the bearings, a vibration sensor is attached to the suspension. In most soft-bearing machines, a velocity sensor is used. This sensor works by moving a magnet in relation to a fixed coil that generates voltage proportional to the velocity of the vibration. AccelerometerAccelerometer
An accelerometer is a device that measures proper acceleration, also called the four-acceleration. This is not necessarily the same as the coordinate acceleration , but is rather the type of acceleration associated with the phenomenon of weight experienced by a test mass that resides in the frame...
s, which measure acceleration of the vibration, can also be used.
A photocell (sometimes called a phaser), proximity sensor
Proximity sensor
A proximity sensor is a sensor able to detect the presence of nearby objects without any physical contact.A proximity sensor often emits an electromagnetic or a beam of electromagnetic radiation , and looks for changes in the field or return signal. The object being sensed is often referred to as...
, or encoder is used to determine the rotational speed, as well as the relative phase of the rotating part. This phase information is then used to filter the vibration information to determine the amount of movement, or force, in one rotation of the part. Also, the time difference between the phase and the vibration peak gives the angle at which the unbalance exists. Amount of unbalance and angle of unbalance give an unbalance vector.
Calibration is performed by adding a known weight at a known angle. In a soft-bearing machine, trial weights must be added in correction planes for each part. This is because the location of the correction planes along the rotational axis is unknown, and therefore it is unknown how much a given amount of weight will affect the balance. By using trial weights, you are adding a known weight at a known angle and getting the unbalance vector caused by it. This vector is then compared to the original unbalance vector to find the resultant vector, which gives the weight and angles needed to bring the part into balance. In a hard-bearing machine, the location of the correction plane must be given in advance so that the machine always knows how much a given amount of weight will affect the balance.
Other types of balancing machines
Static balancing machines differ from hard- and soft-bearing machines in that the part is not rotated to take a measurement. Rather than resting on its bearings, the part rests vertically on its geometric center. Once at rest, any movement by the part away from its geometric center is detected by two perpendicular sensors beneath the table and returned as unbalance. Static balancers are often used to balance parts with a diameter much larger than their length, such as fans. The advantages of using a static balancer are speed and price. However a static balancer can only correct in one plane, so its accuracy is limited.A blade balancing machine attempts to balance a part in assembly, so minimal correction is required later on. Blade balancers are used on parts such as fans, propellers, and turbines. On a blade balancer, each blade to be assembled is weighed and its weight entered into a balancing software package. The software then sorts the blades and attempts to find the blade arrangement with the least amount of unbalance.
Portable balancing machines are used to balance parts that cannot be taken apart and put on a balancing machine, usually parts that are currently in operation such as turbines, pumps, and motors. Portable balancers come with displacement sensors, such as accelerometers, and a photocell, which are then mounted to the pedestals or enclosure of the running part. Based on the vibrations detected, they calculate the part's unbalance. Many times these devices contain a spectrum analyzer
Spectrum analyzer
A spectrum analyzer measures the magnitude of an input signal versus frequency within the full frequency range of the instrument. The primary use is to measure the power of the spectrum of known and unknown signals...
so the part condition can be monitored without the use of a photocell and non-rotational vibration can be analyzed.
See also
- Carl SchenckCarl SchenckCarl Heinrich Johann Schenck was a German businessman who established in 1881 in Darmstadt, Germany the company Carl Schenck Eisengießerei & Waagenfabrik. Today Carl Schenck AG is a subsidiary of the global technology conglomerate DÜRR AG based in Stuttgart.The Carl-Schenck-Award by the TU...
, German businessman - Gordon E. HinesGordon E. HinesGordon Eugene Hines was an inventor of hard-bearing balancing machines and other balancing technologies....
, inventor of hard-bearing balancing machines and other balancing technologies - RotordynamicsRotordynamicsRotordynamics is a specialized branch of applied mechanics concerned with the behavior and diagnosis of rotating structures. It is commonly used to analyze the behavior of structures ranging from jet engines and steam turbines to auto engines and computer disk storage...
, applied mechanics of rotating structures - Tire balanceTire balanceTire balance, also referred to as tire unbalance or imbalance, describes the distribution of mass within an automobile tire or the wheel to which it is attached. When the tire rotates, asymmetries of mass cause the wheel to wobble, which can cause ride disturbances, usually vertical and lateral...
Further reading
- Adolf Lingener: Auswuchten. Theorie und Praxis. Verlag Technik, Berlin und München 1992, ISBN 3-341-00927-2
- Hatto Schneider: Auswuchttechnik. 6. Auflage. Springer, Berlin u. a. 2003, ISBN 3-540-00596-X.