PDL's Microdrive Elite Fibre Optic Feature

APPLICATION BULLETIN - FEBRUARY 1998 | BACK TO INDEX

PDL's Microdrive Elite Fibre Optic Feature - Seeing is believing

Arthur Ede, Arthur Ede Ltd (AEL), inspecting one of the Microdrive Elite's installed on Line 2 at Impact Manufacturing Ltd.

A production line modernisation project is being installed at the Lower Hutt company of Impact Manufacturing Ltd utilising the fibre optics feature of the PDL Electronics Ltd's Microdrive Elite drive is believed to be the first of its kind in the world.

The Microdrive Elite drive has fibre optic communications capability. Fibre optic input and output ports are provided on each drive to enable networking using inexpensive and easy-to-work fibre optic cable. The drives may then be programmed to pass information between themselves via the fibre. This information can be an analogue level such as output current or power, motor speed or torque, reference speed or torque. Also the fibre link can convey digital stop/start, trip and reset signals between drives.

The advantages of fibre optic data transmission are accuracy and noise immunity. Data values are transmitted as digital numbers which cannot be degraded by distance as is commonly experienced with voltage or current signals. Communication is by light pulses which cannot be corrupted by electromagnetic influences such as radio frequency interference, electric or magnetic fields, or lightning strikes.

Impact Manufacturing Ltd manufactures aluminium extruded tubes and aerosol cans for the pharmaceutical, cosmetic and chemical industries. The manufacturing process sees the containers all start out as aluminium slugs which are impact extruded, trimmed, lined internally, painted on the outside, printed and finally covered by a protective over-gloss.

Previously all the production lines were mechanically synchronised by the simple expedient of physically joining each section with drive-shafts, gears and chains. This process, although effective had several drawbacks. It was dangerous (an increasingly important consideration with recent OSH requirements) and required a great deal of maintenance It was also inflexible and time consuming to adapt.

Glenn Love, Development Engineer for Impact Manufacturing, explains that the company is continually replacing and modernising older plant and increasing capacity. The production line in question is referred to as Line Two and consists of four machines. The first is the coater, which takes the just completed tube or can and paints the outside. The second machine, the printer, prints the customer's product information. The third machine puts an over lacquer coating on the can, and the final machine rolls the neck of the tube for fitting the aerosol valve. Between each machine is an oven which cures the paint or printing for about 15 minutes before entering the next machine. The product is conveyed at a rate of up to 80 cans per minute through each of the three ovens by two conveyers with spikes to carry the cans. The design problem was to synchronise the speeds of the machines and the conveyers to allow smooth and damage-free carrying of the product through the processes.

Glenn says "We approached Arthur Ede of Arthur Ede Ltd (AEL), who have done our electrical maintenance for many years and showed him our physical design and presented him with our problem and the process we would like to adopt. As we were already using quite a few PDL drives in other parts of the plant and Arthur had already synchronised two motors using PDL equipment we were happy to have him design the electrical synchronisation design in consultation with PDL Electronics Ltd. However this involved the synchronisation of six motors, which made the project much more complex. The decision was made to use PDL's Microdrive Elite which was just on the market at the time as it offered us a lot more options.

Synchronisation of electrical equipment has been deployed for many years by companies, however, often using more sophisticated and expensive systems than Impact Manufacturing deemed necessary for their operation. Glenn Love believes that their operation is simpler, with a reasonable tolerance for error. "We are currently working on a five percent speed variation to keep everything in synchronisation. This is about a quarter of what we had allowed for in our design. Using this approach, we have brought the cost of the technology down by at least 50 per cent".

Ken McArthur, of Arthur Ede Ltd, makes adjustments to the control of the printer, the central control desk for the whole synchronisation process.

The new process involved installing a Microdrive Elite drive on each of the six motors. The Elite drives were interconnected with fibre optic cable, and were also set up for serial communication control from a Fisher and Paykel Programmable State Controller (PSC). The printer drive was set to closed loop vector speed control mode, which is the most precise speed control mode available. The printer is the most critical part of the whole system and this ensures the printer runs at a constant speed. It is designated as the master drive, and receives a speed reference setting from the PSC via the serial communications link. This speed reference is echoed out to the other five drives by fibre optic. Each of these slave drives have their fibre optic input gains trimmed via serial communications which has the effect of being able to speed trim the motors to maintain synchronisation. Trimming is achieved by counting conveyer product spikes entering and leaving the ovens, and by product reference pulses generated by the machines. By comparing counts, the state of synchronisation can be assessed. If the oven makes a nett gain of two products, the associated down-line machine Elite Drive speed is trimmed by 5% until a nett gain of zero is achieved. AT the point where products leave the oven and enter the up-line machine, the relative position of oven and machine is monitored by a moving proximity switch and moving target. This proximity switch hunts the target and trims the speed of the oven oven Elite Drives. (The 'stand off' method is similar but opposite id direction up-line of the printer.) The design brief set limits of accuracy at this point at +/- 10% but better than +/-5% is being achieved in commissioning. The effect is that the five slave motors are hunting in speed around the level set by the printer drive. The aim of the design was to make the whole system self-teaching so that it would adjust ramp times to give the smoothest response. Additional logic in the PSC allows for loading and unloading the line at the beginning and end of production runs, and for clearing downstream product in the event of a machine stoppage.

When this new section is incorporated into the whole manufacturing line it will include 19 PDL Electronics variable speed drives, which will be responsible for approximately 30 percent of the whole factory output. Glenn Love added " We are also looking at the possibility of using analogue output signals for the Microdrive Elite to provide reference speeds for the other drives in the PDL Electronics product range such as the Microdrive-3 and the Xtravert in order for the speed of the mandrels and rollers on the three islands to be tweaked via the Microdrive Elite drives. The recordable settings are an added advantage as they help us adhere to our ISO 9002 obligations.

Adi Gresslehner, Technical and Development Manager of Impact Manufacturing, comments that even though much of their work involves comparatively small production runs, they must remain competitive as much of their product is exported. This means they have to manufacture a variety of differing size of tubes and cans from 22mm to 53mm in diameter and from 60mm to 200mm in length. It is important that the change over time is quick when changing to a new product, as downtime is unproductive and consequently expensive. The installation using PDL Electronics Ltd Microdrive Elite enables them to separate the individual production machinery and allows a size change to be accomplished in a safe and convenient way on each machine by separate machine setters, hence shorter change-over time. This allows Impact Manufacturing Ltd to be more competitive with overseas companies who have, in most cases, high speed, high cost equipment, but not the flexibility.

Both Impact Manufacturing Ltd and Arthur Ede Ltd praised the professionalism and support they receive from PDL Electronics, on a personal level through the Area Sales Engineer, Brent Sheridan and the technical support. Both companies praise the fact that PDL Electronics is just a phone call away and in the same time zone. Furthermore they all agreed that PDL Electronics Ltd's customer service is excellent with very obliging staff.