Application – Rotary indexing table and robot assembly
7 Minute Read
Fault-free assembly is ensured and downtime minimised by using automated facilities for high volume assembly. Rugged inductive sensors detect the presence and position of equipment or components at each stage to ensure that parts are correctly aligned and ready for the next operation. The sensors must be accurate and responsive. In addition, an IO-Link interface offers the advantages of digital communication without the need for special cabling.
Highly reliable automation and machine-control systems are used to eliminate assembly faults and improve efficiency in an assembly operation. Whilst the repetitive assembly tasks are well-suited to being done by robots, these robots can be too slow at picking and placing the assembled parts and therefore a rotary indexing table is used to move the assemblies between the robots.
The rotary indexing table speeds up the transfer of PCBs between assembly robots and also on and off conveyors, increasing the production throughput and reducing the number of assembly robots required – Sensors are used to automate these processes and these sensors must be able to operate continuously at high speed, performing tasks including: presence detection to initiate the cassette-change cycle in a stack feeder; position control for a rotary indexing table; pick-and-place gripper control; and presence monitoring on a conveyor system.
Stack-feeders deliver base plates, electrical printed circuit boards and other planar components to the assembly lines. In each stack-feeder, a vertical cassette holds as many as 50 individual parts and a single inductive sensor monitors the status of each cassette. Once the final part is discharged from the stack, the cassette moves to its end position, triggering the sensor and initiating the cassette-change cycle.
Contrinex C23 embeddable inductive sensors, featuring a one-piece stainless-steel housing, are both robust and highly reliable. A 7mm sensing distance allows ample operating clearance, minimizing the risk of mechanical collision. Their implementation into the assembly equipment is made easier by the choice of industry-standard PNP or NPN outputs with either a PUR cable or an M8 pigtail connector. Additionally, IO-Link, a standardised point-to-point serial connection protocol for sensors and actuators, is provided at no additional cost, offering the advantages of digital communication without the need for special cabling, making them ideal for Industry 4 applications.
Designed for demanding applications, Contrinex’s rugged C23 inductive sensors offer best-in-class switching frequency of 180Hz and exceptional robustness including impact and abrasion resistance, making them a versatile, cost-effective and highly reliable solution. These uniquely robust sensors are typically demonstrated by Contrinex as being able to repeatedly being used to hammer in nails. Even when their front face is dented, the sensor continues to operate correctly.
Conveyors deliver a continuous stream of parts to the rotary indexing table, which transports them in sequence to each assembly station. As the table rotates, sensors located at precise intervals around its periphery detect its exact angular position, bringing it to a halt once parts are correctly positioned for the next operation.
At each assembly station, automated pick-and-place equipment add components to the assembly. Dedicated transport mechanisms – including vacuum lifters, electromagnetic clamps and mechanical grippers – insert items swiftly and accurately in their designated positions. Embeddable inductive sensors play a key role in confirming the secure closure of custom-designed grippers before fragile, high-value parts are lifted.
Manufactured in V4A/ AISI 316L stainless steel and rated to IP68/ IP69K, these small inductive sensors can be fully embedded into a steel surface such as part of the rotary table or an assembly jig or bench, further reducing the potential for mechanical damage.
On completion of the final assembly stage, finished PCBs are discharged to a linear conveyor system. They travel to subsequent processing stages, including testing and packing. C23 Full Inox sensors mounted directly above these conveyors, detect each unit as it passes below. This check not only confirms the presence of the assembled item at the expected height above the conveyor but also measures throughput by activating a counting circuit in the customer’s control system.
Continuous operation is the norm in automated assembly plants. However, minor adjustments or tool changes may be required from time to time. In non-safety-critical areas, access hatches allow maintenance technicians to carry out these tasks without needing to interrupt production across an entire plant. Multiple sensors, mounted at intervals around the periphery of a hatch, ensure that appropriate warning signals are activated whenever the opening is not fully secured.
The Contrinex C23 series of Full Inox inductive sensors have the capability of communicating remotely with a plant-wide control system, thanks to the implementation of the IO-Link protocol. In a typical automated plant, each assembly line runs continuously throughout the day, with remote diagnostics eliminating the need for manual intervention in almost every situation.
Designed to simplify integration, IO-Link sensors are compatible with all IO-Link master versions, allowing set-up and diagnostics to be conducted centrally. Interrogating a device returns its manufacturer ID and product ID, allowing systems integrators to determine remotely that the right sensor is in the correct location. Contrinex C23 inductive sensors additionally feature an on-demand self-test function that confirms full capability at all times.
For the C23 inductive series, alternating between normally open and normally closed functionality via remote output-mode configuration is a standard feature of the IO-Link protocol. Systems designers also can modify the output signal. Delaying the switching pulse accommodates any travel time between a sensor and its corresponding actuation point, while stretching the pulse ensures that slave devices with lengthy response times trigger reliably, even at high throughput rates.
Finally, each sensor provides an output-status check derived from its factory calibration data. If the output signal from a sensor falls outside a range that corresponds to a sensing distance between 80% and 100% of its nominal value, an alarm flag is triggered, highlighting the need for investigation. For plant managers under pressure, peace-of-mind is a valuable benefit.
The no-cost option of the industry-standard IO-Link protocol ensures that best-in-class performance is coupled with ultimate ease of use in even the most demanding circumstances.