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Product category: Industrial Drives/Controls
News Release from: Lenze | Subject: Lenze model ETC
Edited by the Engineeringtalk Editorial Team on 14 February 2007

Motion controller helps machine stone

A CNC motion controller with a powerful onboard PLC is at the heart of an automation system for a new design of machine that mills complex shapes into stone.

A CNC motion controller with a powerful onboard PLC is at the heart of an automation system for a machine that mills complex shapes into stone The motion controller handles four drive axes and the machine I/O

Although there is also an industrial PC, all the basic functionality of the machine, including monitoring guarding and coolants, is handled in the motion controller/PLC.

Automated Stone manufactures a range of machinery for limestone, sandstone, granite and marble including saws, guillotines and automated lines.

The new ASM machine is designed for the accurate milling of structural stone, for example fireplace surrounds, window mullions and building cornices.

However, it is also capable of decorative panels with images cut in relief, sculptures, wall plaques and lettered signs.

There are four axes: the X-Y axes are in a horizontal plane to position the milling head, a third axis drives the head vertically and the rotational speed of the head is controlled up to 9000rev/min.

Essentially the structure is similar to other types of machine such as depositors and palletisers, but adapted to the size and speed requirements of milling stone.

The cutting tool is polycrystalline diamond with re-circulating water lubrication.

At the core of the machine automation system is a Lenze model ETC which is both a CNC motion controller and a powerful PLC.

The ETC features two CAN communication ports, one used for a motion bus which communicates at a rate of 1MBaud to the X, Y and Z axis drives and the second for a CAN system bus connection to the modular I/O, in this case 16 digital inputs and outputs.

The system bus is a standard feature on Lenze controls so costs are saved as no extra communication modules are required.

The bus also connects to the inverter drive controlling the speed of the milling head.

A further Ethernet port connects to a rugged arm-mounted command station with a touchscreen IPC.

The ETC motion controller is CNC-based, which suits G-codes, the norm for machine tools.

It has extensive and expandable command sets for programming to DIN66025.

As a 32-bit controller, ETC delivers high performance which, in this case, results in high positioning accuracy rather than fast travel.

The onboard PLC takes care of the machine I/O and basic control such as monitoring the coolant pressure and the state of the guards.

The I/O is mechanically integrated into the ETC and is expandable.

PLC programming is done with the languages of IEC61131-3, which are familiar to most designers.

Another advantage of the ETC is the close match to the X, Y and Z axis drives.

They are provided by a Lenze ECS Servo system, comprising a central power supply and three axis drives connected with a shared dc bus.

This multi-axis system gives many benefits compared to individual drives.

Mounting is easy with compact dimensions and a reduction in external components.

Only a single contractor and set of fuses is required.

The drives are capable of safe standstill, in compliance with EN954-1, category 3, where accidental powering up of a motor after a stop is prevented.

Signals from safety sensors can be fed directly to the drives without external contactors, saving on parts and installation time.

There is no need to interrupt the shielded cable to the motor with a contactor.

Restarts are fast and easy, as the power is not removed from the control circuitry in the drive, so immediate acceleration with all the axes under control is possible.

The ASM machine requires smooth acceleration and accurate speed control.

The ECS drives are supplied in a motion version specially designed for co-coordinated motions of multiple axes under central control.

The synchronisation of the axes is performed with a CAN motion bus phase follower.

The interpolation of the motion sequences can be either implemented linearly or as a second order polynomial.

Positioning can be relative or absolute.

The three "axis drives" power Lenze MCS synchronous motors which have a toothed belt connection to a ballscrew.

The horisontal axes use motors rated at 3.8 and 7.5Nm with speeds of 4000 and 3500rev/min.

The vertical axis uses a MCS09 motor rated at 3.0Nm at 6000rev/min and fitted with a permanent magnet holding brake.

The advantages of the MCS motors come from the way the stator poles are wound individually prior to assembly.

This gives a high density of the copper windings, even flux fields and almost imperceptible cogging torques.

Therefore, the motors can be run down to very low speeds whilst delivering smooth torques and the result is a smooth machined finish on the stone work piece.

For simplicity and low cost, the horizontal axes only drive to one side of the machine frame.

To prevent crabbing, a rigid shaft runs across the frame and engages pinions at each end onto racks.

Thus the drive force from the ballscrew is shared to each side.

The milling head is a Saccardo unit rated at 7.5kW and capable of speeds up to 9000rev/min.

Built in is an encoder for positioning and an option for automatic pneumatic tool changes.

Speed control is by a Lenze 9326 vector inverter plus a 9351 brake module to give fast emergency stop.

The inverter is capable of controlling the angular position of stop with a feedback signal from the encoder; the exact angular positioning is necessary for the automatic tool changer.

The operator interface is a Lenze-Digitec IPC , a 15-inch TFT touch screen and seven configurable (customer-specified) pushbuttons, which is mounted on a swinging arm.

This command station has a rugged, machined aluminium and stainless steel housing which is rated to IP65.

This houses a Celeron 400MHz processor and the Windows operating system.

In addition there is a hand pendant for close-up operator adjustments.

There are two purposes for the IPC.

Firstly, it holds the CNC programs for the motion controller and is capable of on-line downloads.

Secondly, it gives 2D and 3D visualisation.

The operator can call up 3D models of the work piece and rotate them on screen.

During machining, the actual cut and the milling head are shown in real time.

The new ASM milling machine takes a different approach to automation with a CNC motion controller that also handles I/O, general PLC control tasks and an interface with a HMI/IPC.

The Lenze automation components are well matched and make effective use of the CAN fieldbus.

Mick Howarth, who founded the company in 1974, said "Our machine is designed for the needs of the UK stone industry, particularly for a long vertical travel".

"Compared to competitors who design for large flat kitchen work surfaces, this new machine is much more suitable for our customers".

"The entire drive and control system is supplied by Lenze".

"As an integrated system, it is easy for the operators and results in smooth and accurate control". Request a free brochure from Lenze ...

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