FAQ - Electric drives

The travel speed of mini slide SLTE depends on the mounting position and the applied load.

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

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

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

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

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

As indicated in the catalogue, both spindle variants can be combined with selected servo motors EMMS-AS, stepper motors EMMS-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.

Yes, but note that only switches SMT-8M (N/O contact) can be used in combination with the MTR-DCI.

Please contact one of our Technical Consultants in your local sales office (tel. 0180 303 3000). They can design your application using the selected drive package.

This is possible when using the MTR-DCI, EMMS-ST or EMMS-AS in the "torque control" operating mode.

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

Depending on the motor controller and the control interface, as many as 5 operating modes with additional functions are possible.

Depending on the motor controller, the following options are possible:

*=+1(homing = positioning record 0)

Only one travel profile is required to ensure that the axis is always moved by the same distance. 

The positioning record table includes a positioning record where the parameter mode is set to RN or RA (relative reference to the last target position or relative reference to the current position (actual position)).

This positioning record is always called up via the rising edge when the digital input is started.

Motor controllers can be controlled via different fieldbuses. If the FHPP protocol is selected (e.g. with CANopen), the positioning records that have been parameterised in the FCT can be activated. If it is necessary to specify flexible positions, the so-called "direct mode positioning control" can be used.

A position and speed parameter will then be specified.

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.

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

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".

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.

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.

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

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.

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.

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.

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.

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.

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

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.

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

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.

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.

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.

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

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

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.

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.

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.

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.

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.

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.

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.

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.

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

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.

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

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

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.

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.