Moving Parts

Optimizing Material Handling Design 
for Assembly and Test Systems

By Angelo Cupani, 
senior mechanical engineer,
 Bayside Automation, LLC 

A material handling system, whether automatic or manual, is the backbone of any production system. When Bayside Automation is asked for assistance in developing an efficient material handling solution, we begin with a list of the project product, process, production, and business factors. Next, we analyze the planned operating parameters associated with each factor, then let these parameters dictate the best material handling system. 

Design considerations

There are many issues to address when conceptualizing a new systems design. Some of the more important and universal ones include line speed, multiple conveyor lines, and “single-up” or “multiple-up” configurations. A single-up configuration includes only one product per pallet, while a multiple-up configuration includes two or more of a product per pallet. The key issue in determining these factors is system cycle time that is usually determined by the customer’s production needs. An estimated efficiency factor is considered in order to determine final machine cycle time. It also helps the customer when systems are designed and manufactured with an intent for six sigma performance. 

Often, manufacturers are faced with deciding on the type of transfer device that should be used. Should a mechanical transfer device be used or would a robot be the better choice? A mechanical pick-and-place device is usually used when a part is moved from one point to another on every cycle. The device typically picks from pallets that stop at the same location or from a cartridge or bowl feeder. Robots, on the other hand, are used when the pick-up point varies each time there is a demand for a part. The parts may be presented to the machine on trays and sometimes on flex or grass feeders, which additionally involves the use of a vision system for guidance. The accuracy with which pieces must be placed can vary from system to system. One customer may require placement with liberal tolerances and another may require micron accuracy.

In one instance, a label was required to be placed on a cover within 0.01-in. accuracy. We used a vision-guided robot to accomplish this. The robot picks the cover from a tray of parts. A camera looks at the label as presented by a labeler, and notes the location and orientation. The robot then orients the cover to suit and presents the cover to the label. Finally, the robot moves the cover with label attached to a second camera where the label placement is checked and confirmed. 

In another instance, a customer needed to place a nozzle on a bottle with micron accuracy. The product, a printer ink cartridge, is used in inkjet printers with a 1200 dpi rating. The system we selected used a highly accurate, vision-guided gantry robot. The bottle was accurately fixtured while the camera noted the fiducial locations on the nozzle. The nozzle was then oriented and placed on the bottle.

A lot of the systems Bayside designs and builds are comprised of a line of machine modules linked by conveyor sections. Each module may include one or more stations that perform individual functions. These stations may include pick-and-place mechanisms, robots, torque drivers, and other devices that a system may need, including welders, ovens, and plybonders. Module designs include safety enclosures that protect personnel from moving machinery. Rotary indexing tables, which are synchronous methods of part handling, lend themselves better to certain types of processes. Modular in-line systems are asynchronous and give a greater degree of flexibility. The indexing table would be used when items need to be rigidly fixtured so that drilling, reaming, and tapping operations can be performed.

Storage buffers

Buffers are a means of designing storage into an automatic system. The size and type are dictated by the part being stored. Buffers essentially come in two types. The first is the last-in-first-out (LIFO) type. In this type, the last item stored will be the first item out. This type is used if retrieving first-stored items is not a consideration or if the buffer is expected to be emptied in a reasonable amount of time. The second type of buffer is first-in-first-out (FIFO). With this type the first item stored will be the first item out, a method used when part tracking is necessary or if the product must be continually rotated.

In response to one customer’s buffering needs, we developed a FIFO system that kept up with production speeds in a very limited space. This design placed the buffer above an existing conveyor line where parts were retrieved from the conveyor and stored. The storage was to take place should a stoppage downstream occur. This allowed the upstream process to continue while the downstream stoppage could be corrected or until the upstream process came to a convenient shut-down point.

Automation supplier responsibilities

The best means of material handling may be obvious, particularly with small systems utilizing few processes. For more complicated systems with many processes, the best method may not be immediately evident. Occasionally, conflicting methods may result, requiring two or more types of material handling techniques. In other situations, there may be reason to propose an alternate process to conform to the preferred material handling system dictated by the majority of remaining processes. This alternative may require iteration and compromise. 

In general, the designer should eliminate or minimize non-value added processes such as transfers from one conveyor to another. The added advantage to this is simplicity—efficiency increases with fewer operations. Once a part is oriented and located, strive to keep it that way. Unfortunately there are many factors that may force a need for transfers. These factors might include the cost of part holders, nests or pallets; processes that need the parts to be stationary, such as drilling, pick and place; as well as processes that need the parts moving such as heating, cooling, and buffers. It’s our responsibility to analyze the system results and provide recommendations and choices to our customers. 

For more information:

Circle 410-Bayside Automation, or connect directly to their website via the Online Reader Service Program at www.RSLeads.com/110df-410

Choosing a Machine 
Loading/Unloading System

By Harold Keichel, President, 
United Index Company

A wide variety of loaders—also known as pick-and-place devices, robots or part handlers—are available in many price ranges. They can be linear (lift, transfer and place) or rotational (lift, rotate and place).

The simplest loader is a single cylinder in which parts are pushed into position. Obviously, unloading can also be accomplished in the same manner. A simple rake-off device can unload parts easily. A more complex variation is one that orients the parts as a function of loading. Round parts can be spun into position with stopping rotation using a pin in a hole or notch. 

The next simplest loader is a single air cylinder that uses a mechanism to give a lift-transfer-and-place motion with one stroke of the air cylinder. A single shock absorber and a switch at the extreme ends of the travel are needed for complete control. Intermediate positions are also achievable. The main advantage of the vertical model is that the mechanism carrying the gripper jaw and part is above the arm, giving operator access for adjustments or other machine mechanisms. A gripper jaw can be operated off the same valve as the loader, simplifying flow control. No sequencing of cylinders is required, so a single contact that is opened by the forward switch (or a timer) is all that is needed to return the loader and operate the gripper jaw.

The traditional lift-transfer-and-place loaders use a vertical slide with an air cylinder and guide rods. At each end position three devices are necessary for fast, smooth operation—one is a positive stop; two, a switch to indicate the slide’s position; and three, a shock absorber needed to slow the speed. A programmable controller or relay logic is necessary to sequence the slide motion in the correct order. 

Another way to accomplish these motions is to power the slide with a servo motor, with power transmitted through a belt or ball screw. Encoders are now needed to slow the motor and bring the slide to a smooth, accurate stop. An obvious advantage to this method is that the slide is now programmable so it is easy to change strokes or have multiple stops if needed. 

For extremely high-speed automation, pick-and-place units driven by cams are used. Although more costly, precision and reliability are usually better. Linear pick-and-place units tend to be quite bulky and with any cam-driven unit cannot be adjusted for stroke changes. For extremely long horizontal or vertical strokes (up to 20 ft and more) and gantry part-transfer operations, linear actuators are used. Consideration must also be given to choose a unit that is sealed and has a rigid bearing system. 

United Index manufactures a unique and versatile cam-guided pick-and-place system. The tool steel cam only serves to guide the motion. Rigidity and accuracy are provided by linear bearings arranged in an XY configuration. Air cylinders, electric or air motors provide power, and sequencing is done via programmable timers. A curved cam path—eliminating the need for shock absorbers and proximity switches—provides rapid, smooth transition from horizontal to vertical motion. Additional features include adjustable down stops, multi-path down positions and walking-beam type motions. Linear strokes up to 20-in. or more are easily achievable. The example shown loads automotive wheel studs into a bearing retainer, with a 2-in. lift, 6-in. transfer and 6-in. down to load four studs at 12 times/min. and a single shift production of over 4000 assemblies. 

This particular operation presented several problems, such as a pick-up opposition four inches higher than the place position. Also, the studs were only 0.007-in. smaller than the insertion hole. Accuracy of the index table and fixtures, along with variations in the studs and housings, made a loader with consistent placement capabilities a necessity. Because this loader has the speed and smoothness required to place the studs, coupled with the dependability required for long-term operations, it was an ideal solution. At this time, over two million assemblies have been completed successfully with this cam-guided loader.

For more information:

Circle 411-United Index Company