Pick it up

Oct. 26, 2006
Servo technology makes pickand-place operations faster and more precise; integrated motion and modular programming simplify their design.

Dan Seger
Global OEM
Automation Inc.

Box loaders use a variety of motors, sensors, mechanisms, and controllers to take finished products from wrappers, cartoners, and fillers and stack them into cases for palletizing or shipment.

Pick-and-place machines are used in a wide variety of applications throughout the consumer products industry. The speed and precision with which they perform their respective tasks directly affects productivity, and ultimately, the bottom line.

Recently, when much of manufacturing moved to servo technology, pick-and-place operations more than doubled their productivity. A similar increase is on the horizon as manufacturers switch to motion-centric control, an approach that integrates motion, logic, and humanmachine interface functions.

Inside the box
The most common pick-andplace machines in industry today are box loaders. Box loaders take finished products from wrappers, cartoners, and fillers and stack them in cases for palletizing or shipping.

A typical box loader consists of three sections or stages. The first gathers products from flighted conveyors or smart belts and assembles them in an orderly fashion for easy picking. The next section, the pick-and-place stage, loads products into cases. A photoeye initiates the action, telling the X and Z pick axes when to lift products and transport them to a waiting case.

Once the case is filled, it is indexed out of the machine and a new case is brought in. The filled case then enters a tape or glue dispenser, which closes and seals the major and minor flaps.

Need for speed
Speed and precision are among the main goals when designing a pick-and-place system. The tighter and more streamlined the motion, the faster and more efficient the system can run.

To maximize precision, pickand-place machines are typically driven by compact, low-inertia servomotors that can quickly accelerate and decelerate X, Z, infeed, and outfeed motion axes.

An ideal hardware platform for such a system is a programmable controller with embedded motion. A typical configuration consists of a Sercos-equipped motion module that connects to servomotors and drives through fiber-optic cable. In addition to optimizing speed, this approach also simplifies setup, automatically configuring the drives (over Sercos) during power-up.

Smooth operation
Another goal when designing a pick-and-place machine is to make it move smoothly. Products must be lifted, transferred, and lowered gently to eliminate damage and extend machine life. If the motion is unstable during transitions, products can slip from the grasp of the mechanical arms that do the work.

The best way to optimize speed and finesse is to employ a controller that moves axes simultaneously, coordinating all motion instructions. The resulting efficient, fluid motion also extends the life of the mechanics of the machine and frame assembly.

Simplifying software
Although pick-and-place applications are fairly simple, they can be design-intensive because of the complex mechanics of the many components involved. However, modular programming techniques that take advantage of templates and standards — such as PackML and Make2Pack-compliant programming — can help cut programming time and costs in half. Using a systematic programming approach based on modules of code that represent different sections of the machine — such as pre-made HMI templates and state models — not only improves programming speed, but flexibility and accuracy as well. And if the modules also contain all routines and local tags necessary for operation, they can create their own links to external tags, making each program fully reusable without having to rewrite tag addresses.

Integrated motion in action

One machine builder serving the food industry recently sought to speed up its pick-and-place operations. Its goal was to reach 300 products per minute using an approach based on two infeeds instead of one.

Having two areas to pick from, however, complicated the design of the motion system and its control. It meant that there would be three motion axes — one vertical and two horizontal — to control through more planes of motion.

The engineers designing the system decided to use an integrated motion approach along with modular programming techniques. In doing so, they completed a project in two weeks that otherwise would have taken a month to make ready for production.

For more information, contact the author, Dan Seger, at (770) 754-8511 or [email protected]

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