FAQ - Electric drives

Electric mini slide

Electric cylinder DNCE

MTR-AC servo drive

Controllers

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Electric mini slide

Which mass can be moved with an electrical mini slide?
The applied load that can be moved by a mini slide SLTE depends on the mounting position of the drive unit.
Horizontal
mounting position
Vertical
mounting position
SLTE-10-... 1.5 kg 0.5 kg
SLTE-16-... 4 kg 2 kg

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How fast can an electrical mini slide travel?
Horizontal
mounting position
Vertical
mounting position
SLTE-10-... 170 mm/s
SLTE-16-... 210 mm/s

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How accurately can a SLTE electrical mini slide position?
The positioning accuracy of the mini slide SLTE lies between +/- 0.1 mm.

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Which acceleration can an electrical mini slide achieve?
The minimum acceleration of an electrical mini slide is 0.5 m/s². The maximum value is 2.5 m/s².

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How many positions can be approached with an electrical mini slide?
31 positioning records and thus 31 positions are possible for mini slides in I/O operation. With bus activation, any number of positions can be approached.

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Why does the KPWR-MC1… supply cable have a sense line when it is not needed by the SFC-DC controller?
The supply cable must have sense function capability for use with future controller generations. When current flows through the supply cable to the consuming device, this causes a voltage drop in the supply cable. The sense lines are used to measure the voltage directly on the consuming device so that the voltage drop in the supply line can be compensated for.

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Electric cylinder DNCE

Is the DNCE with the respective drive package delivered completely assembled?

Yes, Festo can carry out complete assembly if required. Otherwise the drive package is supplied separately.

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Does the DNCE electrical cylinder lock automatically?
The lead screw spindle is self-retarding, which means that slow movements cannot be excluded in the event of vibration. The entire system with the motor unit MTR-DCI is self-locking. The ball screw spindle is never self-locking.

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When using the parallel kit, how is the belt tensioned?

By means of a tightening bolt in the belt housing. The correct belt tension is given in the operating instructions.

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Can max. force and max. speed be applied with the DNCE?

On the version with lead screw (LS), the feed force depends on the speed (see chart in the catalogue).

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Can the drive still be used once piston rod torsion protection has been triggered?

Yes, the torsion protection remains functional. Since the position has changed as a result, homing must be carried out again.

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Can the DNCE also be ordered for a third-party motor?

Yes, this is possible. The shaft is then supplied with a flange for the third-party motor.

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What motors do you recommend for the DNCE?

As indicated in the catalogue, both spindle variants can be combined with selected servo motors MTR-AC, stepper motors MTR-ST and the motor unit MTR-DCI. During the design stage, please note that the maximum speeds and/or feed forces of the electric cylinders will sometimes not be reached as the limits are determined by the motors. For correct DNCE and motor size selection, we recommend the use of the design software Positioning Drives.

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Is it also possible to use proximity sensors with the DNCE?

Yes, but note that in conjunction with the MTR-DCI only SMT-8 switches can be used.

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Can the DNCE, like a pneumatic cylinder, apply pressure with different forces when it has stopped?

This can be achieved using a servo motor in "torque control" operating mode.

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Can the DNCE also be actuated via Profibus?

The drive package with servo motor is available with a Profibus interface.

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MTR-AC servo drive

In how many modes can the MTR-AC servo motor be operated?

The SEC-AC motor controller for the MTR-SC servo motor can be operated in 4 modes.

  • Torque control 
  • Speed adjustment
  • Position control
  • Position control - Synchronous mode 

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Is it possible to switch between modes during operation?

Yes, the mode can be changed with no problems using bus actuation.

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How many travel profiles can be saved in I/O mode?

In I/O mode, you can save 16 travel profiles, inc. homing.

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Can a selected position be passed through at a selectable speed?

Yes, if the variable final speed is not zero, the position will be passed through at the specified speed.

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How many different travel profiles are required to enable the drive to continue travelling the same distance?

For the drive to always travel the same distance, only one travel profile is required, which is then selected repeatedly. The positioning parameter is set to relative.

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How many travel profiles are available for bus operation?

With bus actuation, any number of travel profiles can be written to the controller and then executed.

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Which parameters are used to start up a drive system?

Festo supplies all of the required SEC control parameters on CD-ROM for all drive combinations.

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What is the controller's stop behaviour when the release is cancelled?

The motor brakes with a set gradient and comes to a stop in position control mode.

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What is the controller's stop behaviour when a limit switch is approached?

The motor brakes with a set gradient and comes to a stop in position control mode.

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Can the controller be operated in bus mode without digital inputs?

The inputs for output stage enable and controller enable are also necessary in bus operation.

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Can our servo motors also be used in a vacuum?

A servo motor MTR-AC can also be used in a vacuum if the following conditions are met:

Order a special design with a hole for pressure compensation. In this case, a small hole is drilled in the end cap and a sintered silencer is inserted into it. The motor will still be a standard one, but the modification makes the motor 10 mm longer. This motor can now be used in the low vacuum range up to about 1 mbar, but not in the high vacuum range because of outgassing of the lubricating grease and insulation. Heat dissipation is not the main problem, since around 80% of the heat is dissipated via the motor flange and only 20% via the air. The motor does need to be correctly sized, though, taking into account the workload and the ambient temperature.

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How often can the motor and resolver cable plug connector be disconnected from the MTR-AC servo motor?

The plug connectors are designed for approx. 50 connecting cycles.

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How precisely can forces and torques be controlled with the MTR-AC?

In conjunction with the SEC-AC, our MTR-AC servo motors can be operated in position control, speed adjustment or torque control modes.
It is important to bear in mind that in torque control mode only the motor current is measured and adjusted.
The motor current is proportional to the torque of the motor as long as friction influences are negligible and the motor is not in a state of magnetic saturation.
This means that torque control is indirect and friction influences cannot therefore be corrected. Therefore, the expected precision of the force or torque cannot be higher than the friction forces that are present.

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How hot can a servo motor get?

The motor housing temperature can reach 100°C during operation.
The servo motors are also normally protected by a PTC. The PTC output is connected to the servo controller.
The servo controller shuts down the motor power supply as soon as the internal temperature of the motor exceeds 125 °C.

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Can a servo motor also be used at higher ambient temperatures?

Our servo motors MTR-AC are rated for ambient temperatures up to 40° C, meaning that the power output specifications in the catalogue are achieved up to that point. At higher ambient temperatures less heat can be dissipated. To prevent the motors from overheating at this point, the motors can only be operated at a reduced power output (derating). Derating curves for the motors are available for ambient temperatures of up to 100° C, enabling you to check whether a particular application is still feasible. When geared motors are used, the thermal stress on the gear unit must also be checked.

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Controllers

What does the "Safe halt" function do on controllers of Festo?

The motor is prevented from restarting via two channels.

1st channel: disconnects the controller enable

2nd channel: Interrupts the output stage supply with relay

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Are motor controllers SEC-AC –305 and SEC-AC-508 fitted with mains filters?
Yes, our motor controllers are fitted with mains filters as standard.

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At which cable length are additional mains filters recommended?
An additional mains filter should be installed with cable lengths of around 5 m or more.

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Why is there a stroke reduction when servo-pneumatic systems are used in conjunction with axis controller SPC200?
The stroke reduction at both end positions ensures a minimum air volume, which is needed for reliable positioning. The stroke reserve must be maintained on each side of the drive. The maximum positionable stroke is: positionable stroke = total stroke of the axis – twice the stroke reserve

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Why is my MTR-DCI-32-...-PB not running, even though it is connected to the load voltage?

This error occurs when only the load voltage is connected. The logic voltage for this size and design is supplied through a special adapter (TN 537934) via the Profibus interface. The adapter is an essential accessory for this size. The adapter is not required to operate other sizes (42, 52, 62) with Profibus interfaces. It is only required if the load voltage needs to be isolated from the logic voltage, e.g. for opening a safety door.

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Why do electric drives have an IP protection class, especially for axes?

This takes into account the whole system, i.e. axis, motor and the controller, where necessary.

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What is the main difference between a servo drive and a stepper motor drive?

A servo drive is a regulated system.
The servo motor has a resolver for displacement measurement. There is a continuous comparison between the setpoint and actual position. This means that the servo drive travels exactly according to the specified motion profile.
The servo motor has a high torque over the entire speed range and can be temporarily overloaded by 2-3 times the rated torque.

The stepper motor drive is a controlled system.
Positioning is carried out by specifying the number of control pulses. The torque is reduced over the speed range and if it is exceeded there is a risk of "stepper loss".

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When should I use a stepper motor/servo motor/DC motor?

Servo motors are ideal for high precision and high speeds.
By contrast, if speed and precision are less of a priority, the lower priced stepper motors can be used.

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When is a brake recommended/necessary in the motor?

A brake is normally recommended on a vertical shaft.
This prevents "sinking" of the load if the drive is not released or is not connected to a power supply. There are a few exceptions, such as automatic locking mechanisms, where a brake is not essential.

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Can a motor from another supplier be mounted onto an electrical axis from Festo?

Yes, Festo can produce the axis with a flange for a non-Festo motor.

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Why have the rotor shafts not got a featherkey way?

Festo uses couplings with friction locking. These have zero clearance and are wear-free, with 200% overload protection.
Slot and featherkey connections have major disadvantages for positioning: A certain minimum clearance is required at the side edges (angular clearance) for mounting. This leads to backlash and thus to low positioning accuracy. In addition, the edges are 'deflected' over time, resulting in greater angular clearance between the coupling hub and the motor shaft. Slot and featherkey connections are therefore used on electric motors that operate continuously in one rotation and torque direction and are thus unsuitable for reversing operation.

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What is meant by a resolver?

A resolver is an inductive measuring system.
The functional principle is the same as a generator, i.e. a sinusoidal AC voltage is generated, the frequency of which depends directly on the speed.
This frequency is used by the electronics to calculate speed, acceleration and position.

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What is an incremental measuring system?

In an incremental measuring system, there is no fixed zero point. A homing run must first be used to define a zero point before travel to an absolute position is possible.

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Can the SEC-AC also be used with 115 V AC?

The SEC-AC can also be operated with 115V AC. However, the connected motor will not be able to reach its nominal and peak values at 115V AC.

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Do position errors accumulate with continuous "relative travel"?

The smallest unit of movement of any positioning system is the increment. If it possible to transfer the setpoint position to the controller directly in increments, there is no cumulative error when using relative positioning. If the positioning controller receives the setpoint position as a feed constant calculated by the user, the rounding error results in most cases in a cumulative error.
Positioning errors can also add up if movements relative to the last actual position are repeatedly made. Therefore, on the SEC-AC Festo provides the option of moving relative to the last target position.

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Why is a stroke reserve needed in the case of spindle and toothed-belt axes?

There is a stroke reserve at both ends of the drives in order to leave a safety distance before the mechanical end position.

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Is the stroke reduction for servo-pneumatic systems already taken into account in the stroke of the axis?

No, the maximum settable stroke is:
Positionable stroke = total stroke of the axis – twice the stroke reserve
Important: Maintain the stroke reserve on each side of the drive unit.

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Does the stroke reserve in the case of spindle and toothed-belt axes reduce the working stroke?

No, the total stroke of the axis additionally includes twice the stroke reserve.
Example: DGE-25-500-SP

Working stroke = 500 mm
Stroke reserve = (2x10mm) = 20 mm

Total stroke = 500 mm + 20 mm = 520 mm

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How is the stroke reserve calculated?

The stroke reserve for each end position cannot be calculated. It is a safety distance to the mechanical end position relative to the working stroke used. As a result, there is always a reserve to the mechanical stop, e.g. for hardware limit switches for safely braking the system without hitting the mechanical end position.
The stroke reserve is normally as large as the feed constant for the shaft.

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Why is exact setting of the toothed belt pretension on a toothed belt axis so important?

The toothed belt pretension for a linear axis has a significant influence on its overall performance, particularly on the service life and the skipping behaviour of the belt at maximum load.
In general, an excessive pretension not only unnecessarily loads the toothed disc bearings, but also damages the belt, particularly through the high flexural fatigue loads on the cords.
On the other hand, if the pretension is too low, this leads to skipping of the toothed belt.
The main task of the pretension is therefore to guarantee fault-free meshing of the loose side of the belt, which is almost totally slack with maximum feed forces, with the output disk.

The pretension forces for the Festo toothed belt axes are designed in such a way that this operating behaviour is reliably guaranteed even at the maximum feed force.

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What power supply units are recommended for the MTR-DCI?

What power supply units are recommended for the MTR-DCI?
During activation and when starting up, regulated DC motors have many times the current consumption than during normal operation.
These consuming devices then represent a temporary overload for the power supply.
The nominal current of the power supply should be at least equal to the motor's peak current and, to take account of the motor tolerances, a power reserve of 20 to 50% should be provided.
The exact minimum current limits can be found in the table below for selecting a power supply unit with U/I characteristic curve.


Motor type/Voltage Motor nominal current [A] Motor peak current [A] Power supply unit nominal current [A]
MTR-DCI-32/24V 0,73 2,1 from 3
MTR-DCI-42/24V 2 3,8 from 6
MTR-DCI-52/24V 5 7,7 from 10
MTR-DCI-62/48V 6,19 20 from 15

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How good is the repetition accuracy for spindle and toothed-belt axes?

Toothed belt axes:
DGE-...-ZR +-0.008 mm to +- 0.1 mm
DGEA +- 0.05 mm

Spindle axes:
DGE-...-SP +-0.02 mm

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What is the difference between the following two type designations: DGEL-...-ZR-KF and DGE-...-ZR?

DGEL-25-...-KF is an old designation and describes a toothed-belt axis with a recirculating ball bearing guide (L stands for Laufwagen – carriage).
DGE-...-ZR describes the modular system of a toothed-belt axis in which a recirculating ball bearing guide (KF) can be selected.
The two axes are identical in construction.

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Can I use SME/SMT sensors with the electric axes DGE?

Permanent magnets are integrated in the linear axes DGE-ZR and DGE-SP. This means that magnetically actuated SMT/SME sensors can be used. They can be inserted into the specified sensor slot in the drive profile.

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What needs to be taken into account when using SME/SMT proximity sensors in electric axes?

The SME/SMT sensors have a limited operating path and thus cannot be installed directly in the mechanical end position. Therefore, there is an area between the sensor and the mechanical end position that is not monitored.

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Can I use SME/SMT sensors in electric axes DGEA?

Permanent magnets are not fitted in the DGEA cantilever axis and DGE-ZR-RF roller bearing guide axis. Therefore, SMT/SME sensors cannot be used.

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Can the output signal from the displacement encoder in a DNCI-... drive be read directly into a PLC?

No, the measuring signal corresponds to a raw sin/cos signal in the millivolt range.
Festo offers a measured value transducer that converts the displacement encoder’s output signal into a 0-10 V or 4-20 mA signal.

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What sensors/switches are recommended for electrical axes?

For use in electrical axes, we recommend SIEN-... type inductive sensors.
Appropriate mounting material (HWS mounting bracket) and switching lugs (SF) are available for each axis. These components avoid the undefined area between the reference point, end position point and the mechanical end position.

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How can the DGE axis guide be given additional protection in harsh environments?

The toothed belt axes DGE-ZR-KF, spindle axes DGE-SP-KF and positioning axes DMES are available in a version with dust protection (GA version) in sizes 25 and 40.

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Why is the feed constant for a toothed belt axis so imprecise compared to a spindle?

The feed constant is the axial offset of the axis for exactly one revolution of the sprocket. No tolerances are specified for the feed constant. The influencing factors include the toothed belt pretension setting and the production tolerances of the toothed belt and the sprocket. Thus, the exact feed constant must be determined separately for every axis.

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When does a reference switch need to be used with an electric drive?

Festo electric drives use exclusively incremental displacement sensors.
These sensors can detect changes of position and output them as a sequence of pulses. To determine a reference point for absolute position measurement, a homing run is therefore necessary after start-up. The reference point for this homing run can be a separate reference switch, a limit switch or even a mechanical stop.

With the motor controller for servo motors SEC-AC, one of the two limit switches normally fitted for safety reasons is used for referencing by default. However, it is also possible to use a separate reference switch or referencing to stop.

Activation of the stepper motor SPC200-SMX in conjunction with the stepper motor controller SEC-ST requires a separate reference switch. Use of the limit switches is not possible as NC (normally closed) contacts have to be used here, while the reference switch is set up as NO (normally open). Referencing to stop is not possible as the stepper motor does not contain a measuring system. The control system cannot detect stoppage.

With the mini slide SLT-E and the linear drive HME, as well as referencing to the reference switch, referencing to stop is also possible. To obtain good accuracy, the corresponding rubber buffer should be removed from the end stop. We recommend using a reference sensor that is already fitted in the HME.

The motor unit MTR-DCI is a special case. Here, the position is saved when the unit is switched off. If you can ensure that the drive does not move while switching off, there is no need for a homing run. In conjunction with the positioning axis DMES, referencing to the end stop or mechanical stop instead of to the reference switch is possible with no restrictions

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What is the difference between positioning accuracy and repetition accuracy?

The repetition accuracy defines the deviation with which a position value approached multiple times (under identical conditions) is reached.
The positioning accuracy is the deviation between the positions reached and an agreed, generally applicable length scale. It is influenced by the accuracy of the measuring system used, the residual position deviation of the controller, errors in the feed constant (e.g. spindle pitch) and temperature effects.

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What are the most important advantages of electric drives compared to pneumatic ones?

Electric drives offer excellent flexibility compared to standard pneumatic drives, as they can be freely positioned. They are therefore more comparable with servo-pneumatic drives.
The advantages of electric drives compared to servo-pneumatic are:

  • Higher accuracy, particularly for spindle drives
  • Greater stroke lengths possible with toothed belt drives
  • Higher forces with spindle drives
  • Very high dynamic response
  • Low noise generation

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What is the difference between the DGE-SP and DGE-ZR axes?

DGE-SP:

  • Linear drive with ball screw
  • High repetition accuracy
  • High feed forces (occurrence of force peaks)
  •  High mechanical rigidity to external forces
  • High constant speed 


DGE-ZR:

  • Linear drive with toothed belt
  • High speed and acceleration
  • Large stroke lengths

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Which resolution does a resolver have?

The resolver signal consists of analogue sinusoidal voltages. The resolution is determined in the connected regulator.
This voltage is 16 bit for SEC-AC.
The encoder output at X11 (e.g. for a slave) is forwarded with 1,024 steps per revolution.

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Why is the speed reduced on the DGE-SP axis?

As with all rotating shafts, the bending critical speed is the crucial criterion for length restriction on the DGE-SP axes. With very long spindles subject to high axial force, the buckling load can also be critical in certain cases.
The bending critical speed is the speed at which the spindle executes its initial oscillation. The oscillation amplitudes are very high around the resonant frequency, which causes damage to the ball screw. This results in 'inconvenient' vibration noise. At a reduced speed, extra long strokes can also be made.

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