Motion co-ordinator simplifies dispensing control

Needing a feature-rich motion controller at a competitive price for a new epoxy resin dispensing machine, Newtech chose the MC206 motion co-ordinator.

Needing a feature-rich motion controller at a competitive price for a new epoxy resin dispensing machine, Newtech chose the MC206 motion co-ordinator.

Newtech is a leading designer and manufacturer of robotic systems for resin impregnation, dispensing and encapsulation, with customers across the world in industries such as automotive, electrical/electronic and telecommunications.

Its latest challenge was the design and production of a machine to accurately mix a two-part epoxy resin and dispense it into glass-filled nylon end caps for a heat exchanger assembly.

Critical requirements were for an inherently safe machine with full automation of the epoxy dispensing into two end caps simultaneously, and capable of reliable, consistent production output at around 90 units per hour.

Although an automated end cap feed system was considered, the customer preferred to load the machine and start each cycle manually to ensure every component would be inspected.

This constraint, together with the need for high output, meant that the new machine was designed with two workstations configured for full duplex operation.

Finished parts are unloaded and new parts loaded at one workstation, while the robot is dispensing epoxy at the other workstation, which maximises productivity of both robot and operator.

Access to each workstation is protected by a light guard.

With extensive experience in mixing and dispensing technology, Newtech already understood the ways in which a rapidly setting viscous liquid could behave under production conditions.

The company advised the customer to colour the two components of the epoxy red and blue, allowing an instant visual check that both components were present and had been mixed correctly.

The dispensing system was provided with an auto-purge routine, purging the mixer with fresh epoxy up to five cycles if the machine is left unattended before an automatic shutdown.

Disposable mixer elements ensure that solidified epoxy is easily removed should the machine stop for any reason.

This emphasis on safe, effective handling of difficult materials is a hallmark of Newtech.

"The company has over 15 years experience in this technology", commented Managing Director Bill Ashley.

"We design and build special purpose robotic systems for a wide range of customers.

Each is built to meet demanding international standards, and is expected to perform reliably with minimal maintenance anywhere in the world.

Complex electronic systems and reliability do not always go together, so we have to be very careful in our selection of suppliers.

Trio Motion Technology have always been our preferred motion control systems supplier - in fact, Newtech was Trio's first customer and we have used their products continuously ever since - and it was natural that we should seek Trio's assistance when designing this new machine".

Newtech selected Trio's MC206 motion co-ordinator to control two servo axes and one stepper axis, with two additional CAN 16-I/O modules and a membrane keypad for operator input and machine information displays.

The keypad was considered more suitable for this machine than a computer-style keyboard, simplifying training and improving operator interaction.

"We chose the MC206 because it represents excellent value, having a useful range of features, good reliability and it is easy to program.

Its processing speed make it excellent for high-speed path following, for changing speed and controlling outputs on-the-fly, and its ability to undertake true multitasking is invaluable", continued Ashley.

The machine consists of a dispensing unit with two pressurised epoxy storage tanks, a four-chamber pump driven by a ballscrew and stepper motor for precise volume control, and a cabinet containing the automated mix and dispense systems.

The dispensing heads are mounted on a Cartesian robot of Newtech's own design driven in x- and y-axes by two brushless servomotors via ballscrews.

The mixing heads are raised and lowered to fixed points by a pneumatic cylinder, although they could be mounted on a programmable z-axis infeed slide for dispensing onto contoured surfaces.

In production mode, the operator loads two end caps onto one of two platforms either side of the machine and presses the start button.

While a light guard prevents further operator access to the working area, clamps move to hold the workpieces and sensors signal their correct position.

If the workpieces are present, accurately aligned and clamped securely, the machine then lowers the dispense heads into moulded channels formed within the end caps.

The pump is started and continues to operate at a steady speed until the desired charge has been delivered to the mix/dispense heads.

Following precisely determined paths, the heads lay a bead of mixed epoxy into the channels.

Dwell points are arranged at channel intersections to allow the epoxy to spread.

When this operation has been completed, the dispense heads are retracted and a timer starts, indicated by an orange light.

The operator must wait until this light is extinguished before the workpiece clamps are released and access is allowed.

The delay ensures that epoxy correctly self-levels into the workpiece channels and achieves a consistency that permits the operator to remove the component.

While one side of the machine is performing the dispense routine, the other side is available for workpiece unloading and reloading.

The whole process takes approximately 40s.

If the operator fails to remove the workpieces within a set time, a flashing red light indicates that the epoxy will have exceeded its normal curing time.

"Although the machine is essentially an x-y table with a third axis for the epoxy pump, we have had to consider the conflicting needs of easy operator access and hazards of moving machinery.

The complexity of the resulting safety devices, sensors and interactions between component parts means that the control system is absolutely vital to effective and safe operation", concluded Ashley.

"The Trio MC206 handles this job very well and has features which permit further machine development or reconfiguration if required.

The motion co-ordinator has provided Newtech with a highly flexible solution to our needs".

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