Apex advances accuracy with drive solution

Apex Automation and Robotics, located in the north-western suburbs of Sydney, designs and builds factory automation machinery and robotic systems - from mechanical and electrical design, through to construction and commissioning. Recently, Apex was commissioned to develop an ‘automatic machining centre’ (AMC) for polymer foam panels. Apex teamed-up with motor and drives company SEW-Eurodrive to design a servomotor-based system with faster throughput and greater precision.

Industrial polymer foam is a critical element of a wide variety of structures where lightweight rigidity is required. Produced in varying densities, polymer foam can be used in the construction of wind turbine blades, aircraft fuselages and marine structures, such as boat hulls. The outer skin of these structures is usually made of fibreglass and the PVC foam is glued to the inside of this skin using epoxy resin.

Apex Automation and Robotics was chosen to design and build the machine against international competition. According to the company’s General Manager, Dany Seif, it was the speed and precision of the Apex design that secured the project. “The traditional processing of the foam sheets incurred lots of rejects and needed multiple machines to get the same output,” he said. “We were able to meet the throughput requirement on a single machine and provide the required accuracy of 0.2 mm.”

The AMC forms grooves spaced 20 mm apart along the length of each sheet. Holes are drilled into each groove and spaced 20 mm apart along the length of each groove. The largest sheets can have up to 8,320 holes drilled into the 64 grooves. Half size sheets can be processed at 100 sheets per hour, resulting in more than 300,000 holes being made each hour.

In operation, the design that Apex developed with SEW-Eurodrive provides far greater accuracy than the traditional process, in terms of the positioning of the various cutting tools. A sheet of foam is placed in the AMC and motor-driven saw modules then cut up to 64 grooves in one pass on the upper and lower surfaces. Following this, a bank of drill bits is positioned and then raised to create holes of a pre-determined depth.

All motion processes within the AMC are managed by a single SEW-Eurodrive MOVI-PLC. Combining both conventional sequential PLC control and motion control into a single platform, it links all of the AMC’s motion control elements.

“This is the brains of the operation, where the sequence of movements required for a particular size and weight of PVC foam sheet is programmed and stored. Once the parameters are entered, the MOVI-PLC then choreographs the motion of the saws and drills,” said Apex’s Project Manager Angelo Di Lorenzo.

The two saw modules each comprise a single shaft, along which are positioned 64 blades. Saw rotation is provided by two pairs of motors controlled by SEW-Eurodrive MOVITRAC frequency inverters. Movement of the saw modules along the machining centre is provided by a MOVITRAC inverter/motor combination coupled to a low-resolution encoder.

The 384 drill bits are driven by one large SEW-Eurodrive servo motor. “The hardest thing to design was the drill module,” said Di Lorenzo. “It is basically a massive gearbox with numerous gear chains staged down to one servo motor. With that, you have a lot of bearings requiring high-precision manufacturing.” This motor is coupled to a SEW-Eurodrive MOVIDRIVE ‘B’ application inverter set in ‘speed control’ mode.

The whole drill module itself weighs about 450 kg according to Di Lorenzo. “This whole unit has to be indexed and then inched along very precisely which is why we are using these SEW servo drives.” Movement of the drill module - horizontal positioning along the machine and vertical positioning while the holes are drilled - is controlled by a further two servomotor/MOVIDRIVE ‘B’ combinations. These are set in ‘position control’ mode. “The positioning of the drills on every pass needs to be very accurate,” said Di Lorenzo. “We need to use motor/drive combinations capable of extremely accurate positioning so we can achieve the 0.2 mm tolerance required.”

The SEW-Eurodrive drives all come with spare configurable input/output ports as well as safety stop inputs. A safety circuit, comprising two sets of light curtains and safety monitoring devices, prevents any of the seven drive motors operating when there is something being passed through the entry and exit slots of the AMC. The MOVI-PLC also controls the dust extraction manifold which removes the dust and delivers it to a central collection point.

Only five months elapsed between Apex Automation and Robotics winning the contract and delivery of the first unit. “We like working together as a partnership to design and develop innovative ways of using the latest technology,” said Di Lorenzo. “They [SEW-Eurodrive] have a wide range of product that is readily available and very good technical support.”