Project planning
The more thoroughly a machine or plant project is thought through in advance, the less risk there is of having to carry out expensive modifications during or after commissioning. This applies to both the mechanical and electrical design. This section can only give a rough overview of electrical design. Further information can be found in the publication "Projektierungshilfe" (Project planning aid) under Downloads on our website at www.beckhoff.de
Drive train design
Application, servo drive, motors and gear mechanism must be adapted to each other so that there is an adequate safety margin for all components as a degree of sluggishness appears over time due to high temperatures or wear. Make sure that the components in the working area of the system have adequate reserves so that the working life is not impaired, and the necessary control quality can be maintained.
Control quality, mass inertia ratio and load connection
Control quality is dependent on the parameters "mass inertia ratio" and "load connection":
Control quality / Dynamics | Mass inertia ratio |
|---|---|
Good | 3:1 |
Average | 5:1 |
Bad | 10:1 |
The "Control quality / dynamics" is primarily affected by the mass moment of inertia: a poor "Control quality / dynamic" due to an unfavorable mass moment of inertia cannot be improved even with a very good load connection. Likewise, however, a good "Control quality / dynamic" due to a favorable mass moment of inertia can be reduced through a poor load connection.
Energy management
If the quality of the mains supply is impaired due to wide fluctuations in voltage, then both the servo drive specification and the speed range of the motor will need to be considered. With a positive tolerance for voltage fluctuation the upper limit value of the wide voltage input of the AX5000 needs to be considered. With a negative tolerance of the voltage fluctuation, it must be checked whether the decrease in speed caused by the low voltage is permissible. With these motors what is known as field weakening operation (check availability) of the servo drive may provide a solution. If the mains supply does not meet the specifications for operation of the AX5000, then isolating transformers, mains chokes, mains filters or other measures may be required. An energy efficient drive system operates in a drive system with a shared DC link and shared internal and possibly also external brake resistors or brake modules. If you are already using similar drive systems, the AX5000 offers a convenient diagnostic system for determining the load on the brake resistors and for transferring the values. Previous experience with drive systems shows that in such a system much smaller or even no external brake resistors / brake modules need to be used.
EMC, earthing, screen connection and potential
The AX5000 corresponds to EMC category "C3" (industrial sector) in terms of conducted interference emissions. If you wish to use components which comply with a higher category you can limit the AX5000 conducted interference emissions with the aid of additional filters to such a degree that this complies with the EMC category "C2" (residential and industrial environment) or "C1" (residential environments). Ensure that there is adequate earthing (large-area low-impedance connection) of all relevant components (incl. control cabinet). The AX5000 incl. periphery, control cabinet, machine bed and motors must be at the same potential, as the AX5000 control quality will suffer under differing potentials and operational malfunction may result. Using the screen connection for potential equalization is not permitted. If you are unable to provide a uniform reference potential, you need to lay potential equalization cables of adequate dimensions. Smooth operation is only guaranteed by faultless screen connections of the cables. The screens must be applied generously at both ends and must on no account be disconnected. Use pre-assembled Beckhoff motor and feedback cables as these are optimally adapted to the drive system and reduce interference to a minimum. Ensure that the connectors are properly connected: this applies to the motor connector.
Control cabinet
The dimensions of the control cabinet must be sufficient to accommodate all components with the specified distances. Remember that high temperatures may necessitate forced cooling. Position the control cabinet as close as possible to the machine so that the motor cables can be as short as possible. In addition, the control cabinet should have an earthed metal rear panel to which the AX5000 incl. periphery are attached so that safe earthing can be guaranteed. If you are unable to guarantee these conditions, you need to earth the AX5000 and the relevant components using an approved cable of adequate size.
Motors and cables at servo drives up to 25A
Motors with max. 400 V rated voltage:
If the length of the motor cable is ≥ 25 m, then a motor choke is required for each motor.
Motors with max. 480 V rated voltage:
If the length of the motor cable is > 20 m, then a motor choke is required for each motor.
The control cabinet should then have adequate space for motor chokes. In exceptional cases (sensitive sensors etc.) it can be necessary to use a motor choke even for motor cable lengths < 25 / 20 m. Lay the power and signal cables in separate metal cable ducts or, if both types of cable use the same metal cable duct, make sure there is an earthed metal dividing wall between the cables.