Drive technology
'Smart Motor' reduces variant diversity by up to 70
Conveyor technology places very specific demands on drives. With both mains-operated and controlled motors, the user has therefore inevitably had to make compromises to date. Not so with a 'smart motor'.
Smart motors help to reduce the number of variants - for example due to the freely adjustable speed, the integrated soft start functionality and the reduced wiring as a result of the electronic contactor and motor protection function.
© LenzeConveyor applications pose a number of challenges for drive technology. These result from three different phases in the movement of the conveyed goods, which place very different demands on the motor. A high breakaway torque must be generated for starting in order to accelerate the loads. In the case of a roller conveyor in pallet technology, several tons of mass can quickly accumulate and need to be set in motion. Once the target conveying speed has been reached, only the friction of the mechanical construction needs to be overcome. Much lower torque values are sufficient for these constant speeds. This changes again when braking or aligning the pallets, when they are moved to the stop and the rollers or chains have to briefly slip under the pallet with high frictional resistance.
Around two thirds of drives in conveyor technology are geared motors that are operated directly on the 50 Hz mains using contactors or motor-starter combinations. Their output must be designed for the starting torque. This in turn means at least one size more than would be necessary for stationary operation. As a direct consequence, the acquisition costs increase unnecessarily.
Since 97 % of the costs of a drive are attributable to the energy requirement, the issue of energy efficiency is even more important in this context. And this is where it pays off if the drive is actually oversized. Even IE3 motors, which are equipped with a lot of iron and copper and are therefore more expensive, are not efficient if they are not operated at the rated point (rated speed / rated torque) but in the partial load range. However, the rated point is never reached in conveyor technology - neither during acceleration, nor during constant speed, nor during alignment. In applications with frequent start/stop cycles, the supposed energy efficiency advantage even turns into a disadvantage: Due to the higher mass inertia, these motors require more energy to accelerate back to operating speed.
The Smart Motor at Swiss chocolate manufacturer Camille Bloch: Thanks to its quadruple overload capacity, it can easily cope with the high breakaway torques in pallet transport.
© LenzeAround one in three drives in conveyor technology is controlled by simple frequency inverters. These already provide partial relief when selecting the right motor dimension, but cannot completely bridge the difference in required torques between acceleration and constant running. This is because the frequency inverter typically only provides around twice the overload for up to 5 s (180 to 200 %) during the start-up process. However, significantly higher values would be required, even if only for one second. In addition, although the investment in the conveyor drive - or the geared motor - is cheaper with a simple frequency inverter, the costs for the inverter are added. And here the user often has to pay for features and functions that he does not need. These include, for example, standard drive functions in the inverter such as process control, blocking frequencies or different motor control modes. The complexity of the solution may also increase. To put it in a nutshell: none of the solutions shown are ideally suited to the requirements of conveyor technology.
More economical than IE3
The problems described can be circumvented with modern drive concepts such as the 'Smart Motor' from Lenze. With this approach, the electronics and software are specially tailored to the motor - unlike conventional solutions, which are usually based on a modular principle and in which one set of electronics is used for different motors. This means that the electronics, software and motor are not optimally adapted; the software settings in particular are only moderately optimal.
As a fully integrated solution with its own electronic controller, the Smart Motor is not subject to the requirements of the European energy directives - but is nevertheless more economical than IE3 motors as a result, as it can be dimensioned based on the required power in constant operation. The lower mass and dimensioning of a smaller motor also saves on expensive materials. Operating costs are also reduced, as the motor runs in the optimum power range for most of the time. The motor still delivers the higher torque required for acceleration or alignment - up to four times the nominal torque - thanks to the integrated electronic control.
The electromechanical properties therefore differ considerably from directly controlled drives, as well as from those that are operated by frequency inverters - to the benefit of the system operator, who has to use less energy due to the improved efficiency. In addition to the energy-saving aspect, the solution described also promises significant advantages in terms of project planning and development on the part of the OEM.
Up to 70 % fewer variants
Two Smart motors with adapted connection technology are installed offset in a conveyor and lifting unit in the Camille Bloch logistics center at the Courtelary site.
© LenzeEvery geared motor that is operated on the mains via a contactor must be adapted to the required conveying speed using the gear ratio. This results in systems with a large number of different geared motor variants. The development engineers also have to take into account the different mains frequencies (50/60 Hz) and different energy efficiency regulations in the supplied market regions - a high administrative effort that runs through the entire product life cycle: from engineering (parts lists, design) to materials management (orders, warehousing) and logistics (worldwide (service) availability) to operation and maintenance (training, spare parts stockpiling). Ultimately, the risk of errors increases with the number of variants, as mix-ups can occur more easily.
This is where the electronic control of the Smart Motor pays off in several ways. This allows the drive speed to be adjusted with the same gear ratio. The consistent, universal design of the drives for all standard conveyor elements reduces the number of variants by up to 70 %, which also facilitates modularization in engineering. Another contributing factor is that the electronics can cope with mains voltages from 400 to 480 V, meaning that the same design components and even the same conveyor modules can be used for different regions (e.g. North America and Europe).
If it turns out during commissioning or later optimization of the conveyor line that the transport speed needs to be adjusted, this is also no problem. The setting can even be made from a smartphone via NFC. In addition, the smart motor has greater scope for adjusting the speed range than a geared motor, for example, which may have to be replaced completely if the speed to be achieved deviates too much from the planned value.
Switch cabinet only half the size
However, comparing the Smart Motor with gearbox or VFD drives solely on the basis of technical features falls short. The differences in design have massive consequences for machine and system engineering, as numerous components can be omitted due to the integrated functions. These include parallel cabling, reversing contactor and motor protection circuits for mains motors. With these, each motor needs its own supply line from the contactor. Forward/reverse operation and different speed levels (normal operation, approaching stops) must be realized with pole-changing motors and reversing contactor circuits, which either take over motor protection functions themselves or otherwise must be combined with corresponding circuits. These functions can also be provided by a frequency inverter, but this incurs additional investment costs, requires specially shielded motor cables and also takes up space in the control cabinet.
The Smart Motor, on the other hand, is equipped with integrated electronics that provide four speed levels in different directions of rotation and motor protection. Switching takes place via 24 V signals - and is therefore 'fieldbus-neutral'. In addition, the 400 V cable can be looped through to other drives, which significantly reduces the amount of cabling required. As a result, the control cabinet can be considerably smaller - in practice by up to 50 %. But that's not all: thanks to the pluggable connection technology, which makes opening the terminal box unnecessary, the motor can be connected without errors in a matter of minutes. Predefined speeds and acceleration ramps can be transmitted wirelessly via smartphone - without the need for expert knowledge or time-consuming employee training.
Torque and current surges are avoided
With line-commutated IE3 motors, a significantly higher starting torque is noticeable, which these motors have due to their design compared to previous IE1 or IE2 motors. This high starting torque affects both the mechanics and the gearbox and leads to more wear and therefore higher maintenance costs and even mechanical overloads. With adjustable acceleration and deceleration ramps, the Smart Motor avoids such torque and current surges during start-up. This protects both the mechanics of the conveyor belt and the conveyed goods.
Braking is also electronically controlled. This means that a constant braking distance is always maintained, regardless of the load. The light barrier for the stop signal is therefore always mounted in the same place. Last but not least, an (optional) holding brake is integrated. Unlike mains motors, where the brake is activated at full conveying speed when the contactor drops and the braking distance is load-dependent, the Smart Motor has a high stopping accuracy of just a few centimetres and does not have to perform any mechanical friction work. Accordingly, there is no wear and maintenance required at this point to readjust the brake or readjust the light barriers. The user also does not have to worry about the brake voltage, brake rectifier and brake logic - the Smart Motor does this itself.
Author:
Tim-Oliver Ricke is Global Segment Manager Intralogistics at Lenze.
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