Drives and Controls Magazine
Control Techniques unveils new-generation Unidrive
Published:  01 September, 2002

Control Techniques unveils new-generation Unidrive

Control Techniques has unveiled the successor to its multi-function Unidrive which it launched in 1996. Although the new SP model keeps the Unidrive name, it has been redesigned completely, with many features being added following surveys of what customers - particularly OEMs - want from a systems drive.

The result is a modular design that combines drive and PLC functions and offers facilities including:

.• a choice of V/f, open- or closed-loop vector, servo, or regenerative operation (with power factor control);

• built-in support for 14 different types of feedback device;

• the ability to accept up to three plug-in "solutions modules" such as application co-processors with PLC functions, I/O modules, extra encoder interfaces, and fieldbus adaptors;

• the facility to operate from a 48V DC supply;

• a plug-in SmartCard that can be used to transfer parameter settings between drives;

• a choice of LED or LCD keypads (or no keypad at all);

• the flexibility to operate in centralised, distributed or mixed control architectures; and

• a "secure disable" function which allows the drive to be used in safety installations without an external contactor.

Control Techniques has spent more than three years developing the new Unidrive (shown above) at a cost of over $5m. The company claims it has created "a new benchmark for AC drive performance" and contends that the drive "marks the evolution for AC drives from dedicated controllers of speed and torque, to fully-fledged solutions platforms in their own right".

The design was guided by customer surveys which revealed that although users liked the idea of different drive technologies in one package, "they wanted more power in terms of PLC and mathematical functions," reports Phil Sewell, CT`s executive vice-president for sales and marketing.

They also wanted drives that were easier to integrate and had better compatibility with bus and encoder technologies, Sewell adds. "Our competitors didn`t have what they wanted," he suggests.

According to Professor Bill Drury, CT`s executive vice-president for technology, the new drive "will control almost any motor" (other than DC or stepper types). Its 32-bit RISC processor is twice as fast as its predecessor and the drive updates its speed loop every 250µs. It has a bandwidth of more than 150Hz.

OEMs can adapt and tailor the drive for particular applications. Certain key functions are standard, and others can be added using plug-in modules.

One of the new drive`s more unusual features is its "secure disable" (SD) facility, which allows it to be used in a machine safety installation without the usual isolating contactor. Instead, a high-integrity circuit monitors for any failures - such as an exploding capacitor - that might disable the drive. This avoids the need for the electrical isolation traditionally provided by a contactor to prevent a motor shaft from turning in such circumstances.

The SD facility is independent of the drive`s firmware and is said to meet the requirements of EN954-1, category 3 as required by the Machinery Directive. The SD function has been tested and certified by the German BIA institute for work safety. Drury won`t divulge how the SD function works, except to say that "it is not a simple matter" and that it involves the design of the drive`s plastic mouldings.

Another unusual aspect of the new design is a 48V DC supply input at the top of the drive. Using this, the motor can be run at a slow speed allowing, for example, lifts to be driven from an emergency battery when the mains supply fails. Other potential applications include limiting operating speeds when setting up robot cells, removing material safely from machines, and operating in low-voltage installations.

The 14 software-selectable feedback options supported as standard include quadrature/pulse encoders, EnDat, Hiperface and SinCos encoders, SSI absolute encoders, and frequency and direction encoders. CT contends that the Unidrive SP the first drive where the OEM does not have to worry about what type of feedback may be used, or to pay for and install, extra cards.

Resolver feedback can also be provided by plugging an interface into one of the three SM (solutions modules) option slots on the front of the drive. The slots can also accommodate a second universal encoder input module. All of these modules (shown above) are colour-coded.

One of the key roles for the slots is to accept fieldbus adaptors. Initially, CT is supporting Profibus-DP, DeviceNet, CANopen, Modbus RTU, and Interbus, as well as its own high-speed CTNet system. Next year, it plans to add Ethernet and Sercos adaptors.

The drive can act as a gateway between the different bus systems, eliminating the need for costly interfaces. It can be used in either centralised or distributed control architectures - or in hybrid installations with different buses serving different sections.

The option slots can also accommodate SM-Applications modules that provide PLC-like functions to reduce the load on external PLCs or PCs - or to eliminate them altogether. Drury claims that the performance of the real-time, synchronised controllers is "better than a PLC".

Users can build applications from a CT library of more than 150 function blocks, including cam and PID functions, or use ready-made packages for applications such as winders, flying shears and fan and pump drives.

To minimise initial costs, the Unidrive SP does not offer on-board programming as standard. If users want this facility, they can attach a low-cost LED keypad or a more sophisticated LCD version, or plug a PC into the Modbus RTU port on the front of the drive.

Every drive comes with a SmartCard which plugs into a slot in the front (shown above). The card can transfer complete sets of hundreds of parameters from one drive to another. The cards, which can hold up to four sets of parameters, can be programmed using desktop writers, thus simplifying drives commissioning. The cards can also store predefined application macros such as brake control functions for cranes.

Other facilities offered by the new drive include: built-in EMC filters; thick-film braking resistors which slot into the heatsink; a 24V control supply input to maintain power to the control, fieldbus and encoder modules during commissioning or a power failure; a switching frequency of up to 16kHz; and the use of low-loss trench technology output stages.

The drives are dual-rated. For normal duties, such as fan and pump drives, they can withstand a 110% overload for 60s. For heavy-duty applications, they can handle a 150% overload for open-loop applications, and 175% for closed-loop. "We`re not skimping on amps," declares Drury.

The drives have been designed to be easy to install, with specially-designed cable supports, and slots provided for terminal block markers. "From an installation point of view, it`s a cabler`s dream," says Sewell.

The new Unidrive is being introduced in two stages. Initially it will be available in three frame sizes from 0.75-30kW, in voltage ratings of 220V, 400V, 575V, 500/600V and 500/690V. Three more frames will be added next year, taking the maximum rating up to 1MW. Although the smallest frame size is slightly wider than its forerunner, the larger frame sizes are more compact than their predecessors. Prices will be similar to the corresponding earlier models.

The original Unidrive will continue in production for about a year. Programs from this version can be transferred to the new model with a few tweaks. CT can supply software to perform the "translation".

Sewell says that the original Unidrive has been "a great success". It now accounts for about 60% of CT`s business and has helped to give the company more than 15% of the European systems drives market, he adds. About 30-40% of Unidrives are now used in the servo mode, justifying the extra cost of including this option, Sewell argues.

Although the UK now accounts for just 5-8% of Control Techniques` business, the company will be manufacturing the new Unidrive at its Newtown, Wales, headquarters. However, it is transferring production of some lower-cost drives, such as the Commander SE, to a Chinese factory, acquired by its parent Emerson Electric. As well as cutting production costs, the move will help CT to penetrate the Chinese market.

Sewell expects about 60% of Unidrive SP sales to be to OEM customers. The remaining 40% will be split between systems integrators and "professional end-users", such as food manufacturers.

The new drive is being launched initially in Europe, and later in the North American and the Asia-Pacific regions. Control Techniques` sister company, Leroy Somer, will be selling badged versions of the Unidrive SP and CT is talking to at least one other potential badging partner. .