Automate with air

By R.T. Schneider, editor

Reports and comments about examples of how versatile pneumatic components and systems can improve productivity via simple automation projects.

Rotary automation - it's all in the valve

The major objectives of automation are to reduce the number of manual operations, increase the production rate, and simplify the process - usually while running continuously. Clean compressed air can safely operate a broad variety of automation functions. However, in pneumatic applications on rotating machinery that require on/off flow control, the piping and system interlocks can become complex. Because of this, some designers may shy away from using pneumatics on rotating equipment.

Actually, rotary process control valves - such as our SRS Rotary Timing Valve (RTV) - can easily achieve automated functions and eliminate complex control systems where one sector of a machine turns in relation to another. Serving as a combination manifold and sequence-control valve, a single one of these disk-type valves - built with one or multiple predetermined sequences - can automate on/off control of flow to one or more pneumatic devices during continuous-rotation or indexing motions.

For example, the familiar pick-and-place function in a transfer line requires actuation of the holding device, followed by continuous holding of the part in this device until it reaches the position where the part is to be placed, and then releasing the part from the fixture. The Rotary Timing Valve can do this automatically as relative motion between the two valve halves opens or blocks pressure and exhaust ports as required. Each of the several holding devices is actuated as it enters the circuit; then each device, in sequence, will release its part as the air is vented at the appropriate position. A single holding circuit can control a single-acting cylinder (or cycle a venturi vacuum generator). A second circuit would be needed to operate a double-acting cylinder - the first circuit for clamping, the second for unclamping.

If a rotary table has four stations, each with a double-acting-cylinder, the conventional control would call for an 8-port rotating union and separate valves for each cylinder to perform this same function. (With more positions on the rotary table, more controls would be needed to perform even this simple function.) A single pneumatic RTV sequences the identical function more easily, automatically, and at less cost.

If the application calls for external control, the function can be provided and simplified through the RTV. Provision can be made for very precise timing if required. Other special controls also can be integrated into the valve function, reducing the number of external controls generally required. Costs and system maintenance are significantly reduced through such system simplification.

Of course functions other than part-holding may take place on rotary tables. These could include operation of air motors, clutches, collets, chucks, push rods, brakes, and even air blasting. Any of these functions that require on/off flow control during 360° rotation can be handled automatically with RTVs.

The final configuration of these valves depends on the number of circuits involved, port size, and any special installation considerations. These might include such features as: a center bore to allow a shaft or electric wiring to pass through the valve; flanges to attach the valve to the equipment or to a stationary post or framework; or ancillary attachments such as an electrical slip ring. Location of the pneumatic supply ports can be customized to the particular application.

Another possibility: these valves can be designed to handle multiple fluids - both gases and liquids - in the same unit. Provision can be made for complete isolation of each fluid, and vents, barriers, and internal drains can be incorporated in the valve.

Whether basic or enhanced, Rotary Timing Valves can solve automation problems on rotating pneumatic equipment by minimizing system complexity and maximizing simplicity of operation.

Claire S. Goodwin, vice president, sales engineering, Scott Rotary Seals, Inc., Hinsdale, N.Y., provided this discussion of her company's products. Scott has registered SRS as a trademark, and applied for trademarks on Rotary Timing Valve and RTV.

Pneumatics teams with electronics to run quality test

No one pays much attention to the daily miracles that ubiquitous office photocopier machines perform, but if something goes wrong, operators become enraged. To survive, copier manufacturers must strive to minimize any type of downtime wherever possible, not only in performance of the basic machine, but also with all the extra features now included. This has resulted in the use of modular cartridges for a variety of functions, including automatic stapling. When the staples in a cartridge run out, the operator simply replaces the old cartridge with a new one - no fuss, no mess, no delays.

Acco USA, Long Island City, N.Y., makers of Swingline office products, supplies some of these police-whistle-shaped staple cartridges. Automation Engineer Vladimir Barmas says, "To assure optimum quality control of our cartridges, we wanted to design a machine which would combine multiple quality-test functions in a single, stand-alone unit. Up to now, customers performed their own cycle testing of their machines. By doing the quality-control tests on the cartridges in our plant prior to shipment, we provide added value to our customers, saving time in their final operational test procedures."

Acco's test sequence called for six basic steps after the cartridges were loaded onto the unit:

* checking the casing for correct dimensioning and alignment between upper and lower pieces
* ensuring that the staple roll is present
* testing the pull force required on the staples to extract them from the cartridge
* ejecting cartridges which fail the test
* labeling cartridges which pass all tests, and
* transferring passed cartridges out of the unit to the packaging line.

Acco engineers decided to design a fully automatic electropneumatic system. This could exploit the speed, cleanliness, and wide variety of pneumatic actuators available to generate motion throughout the unit, while taking advantage of electronic programmability, integral diagnostic functions, and easy preparation of test documentation. Electronics also could interface with an optical system to confirm the presence of a roll of staples inside the cartridge and the instrumentation that measures the pull force. They chose an Allen-Bradley SLC 5/03 programmable logic controller and DH-485 protocol to provide supervisory control of the whole operation. This includes meshing with the machine that assembles cartridges and feeds them to the test unit, as well as sequencing each step in the test process.

The engineers worked with Festo Corp. to select the pneumatic cylinders, slides, rotary actuators, and grippers that move the cartridges, and develop appropriate circuits and controls. "Designing the pneumatic pick-and-place/transfer mechanism was one of the most challenging problems the engineers had to face," says Barmas. A horizontal 25-mm bore DZH traverse cylinder with oval piston strokes 320 mm to carry four pick-and-place modules that extend downward at right angles to its rod. The modules are spaced so that the distance between them is the same as the distance between the test stations below them. When the traverse cylinder extends, it positions one pick-and-place module over each test station. When the traverse cylinder retracts, it indexes each module one station to the left. Cartridges start at the loading station and progress through each test station sequentially, carried by a very simple linear motion. Cushions and shock absorbers minimize impact forces, and the cylinder's oval piston prevents rotation of the rod to maintain proper alignment.

The pick-and-place modules also incorporate DZH cylinders. In this case, the cylinders have hollow rods with suction cups fitted on the lower ends. When the traverse cylinder completes its stroke, the module cylinders extend to bring the suction cups into contact with cartridges at the test stations. Then, venturi vacuum generators cycle to draw air through the rods and create the vacuum that grips and holds the cartridges during transit. (This piping arrangement eliminates much of the tubing found in vacuum systems with mechanical pumps.) Festo Type PEN vacuum-electric transducers in each module provide the feedback signal to the PLC that a part has been picked up.

Commands for the valves that operate the actuators and vacuum generators are delivered from the PLC via Festo's Compact Performance (CPV) manifolds. These modular manifolds include a fieldbus interface with simple plug-in connections. Twisted pairs of fieldbus cables - up to 5 m long - connect the separate modules. This configuration allows engineers to decentralize the manifolds, mounting them close to the actuators they control.

Here's the operating sequence of the cartridge-test machine. With the traverse cylinder extended full stroke to the right, all four modules are positioned over test stations. They all then extend to pick up a part. Initially, there is a part in position only at the loading station, with none at the other stations yet. Electronic inductive sensors are mounted at each position to detect presence of a cartridge and send a signal to the PLC. If no part is in place at a station, the PLC does not turn on the venturi generator for that module. As additional cartridges are picked up at the loading station, all four stations become occupied and all the test functions are implemented.

A pneumatic slide or twin-piston clamping cylinder holds the cartridge at each test station. At station 2, pneumatic cylinders extend three digital height probes until they touch the top of the test cartridge. Properly dimensioned cartridges measure within a ±0.006 in. tolerance of the set-point height. Another pneumatic cylinder ejects any out-of dimension cartridges.

Good cartridges are picked up and moved to the next station. There, an optical system confirms that a roll of staples is present inside the cartridge. Testing the staple extraction force at the next station presented the engineers with another unique design problem. They solved it by using a pneumatic rotary-actuator/gripper combination, attached to an independently operated strain-gage instrument. The acceptable nominal force for extracting staples from a cartridge is 150 g ±35 g. Cartridges that fail the pull-force test are ejected by a pneumatic cylinder.

If the cartridge passes the force test, the 1-in. long staple test strip, which was extracted from the cartridge and is still clamped in the gripper jaws, is twisted off by rotation of the rotary actuator. Passed cartridges then move to the final station where they are dated and labeled by an independently operated labeling machine. Finished pieces are picked up and placed onto a chute in preparation for packaging.

According to Barmas, total time to design and build the first prototype test unit was only ten weeks. Other machines are planned for larger cartridges. Each test unit has the potential to test 10 to 12 pieces per minute, or as many as a million per year. Besides the primary advantage of providing customers with 100% tested cartridges, the new machine does not require a dedicated operator - saving on labor, time, and costs, and eliminating a boring, repetitive, manual process that formerly used as many as three people.

Richard Day, director of marketing, and Bill Uihlein, applications engineer, Festo Corp., Hauppauge, N.Y., described this pneumatic test equipment.

Air logic automates pneumatic balloon-imprinting process

Balloons have become a popular part of many American celebrations - birthdays, anniversaries, job promotions, childbirth. And to make each event more special, the balloon can be custom imprinted. Greeting-card stores and other retail outlets offer this service, and balloon manufacturers imprint their products on a larger scale. In all cases, however, this process has traditionally been accomplished by manually operated machines, even when producing mass quantities.

To operate these machines, the balloon is first inflated. Then a silk-screen device is positioned and operated to place the ink on the balloon. Finally the silk screen is moved out of the way and the printed balloon is removed. Because this operation called for so much manual handling, it greatly limited output, while maximizing labor and time.

Ardent Merit Co., Inc. of Rancho Cucamonga, Calif., a manufacturer of balloon-imprinting equipment, recognized that there was much room for improvement in this procedure and decided to develop a method that would automate it. Through local Parker Hannifin distributor S&S Fluid Power of Carson, Calif., Ardent Merit worked with Parker's Pneumatic Div. and Parker's CAD-based engineering programs to design modern imprinting equipment that uses automatic controls.

Because compressed air - between 40 and 60 psi - must be delivered to the machine to inflate the balloons, it was natural to use air-logic controls to run it and pneumatic components to produce the mechanical motions. The new machine's air-logic system is sequenced by pneumatic timers (which allow convenient adjustments for different applications). The air logic approach costs much less than electronic control and provides a trouble-free system with self-diagnostic capabilities.

Operation of the new machine is simple. The operator manually places the balloon over an air nozzle, then initiates the automation cycle with a pedal. First, the balloon inflates; next, standard air cylinders position the silk-screen frame against the balloon surface; then, rodless cylinders stroke the squeegee that actually applies ink to the balloon; and finally all cylinders return to their initial positions and the balloon deflates. The operator then removes the imprinted balloon and places it in an adjacent drying chamber. If images are required on all four sides of the ballon, the operator can select a cycle that rotates the air-nozzle assembly in 90° steps - via a rotary actuator - and repeats the imprinting process on each side automatically.

The final design sits in a ProFrame structural framing system from Parker's Automation Actuator Div. The Tele-pneumatic air logic, Schrader Bellows control valves, cylinders, and FRLs are manufactured by Parker's Pneumatic Div. S&S Fluid Power provided pneumatic-cabinet building capabilities and other assembly work on the units.

Ardent Merit offers these machines (with patent pending) in several configurations: multi-nozzle units imprint balloons in the large quantities needed by manufacturers, smaller units perform in retail stores. The old manual machines could produce at best about 60 to 100 balloons per hour. The new automated multi-nozzle machines can handle up to a half-dozen balloons simultaneously and imprint between 500 and 600 units per hour. The key to the success of this project was the ability to incorporate standard pneumatic componentry into a unique design that produces the desired end result in a cost-efficient manner.

Pat Angotti, a pneumatic application engineer with Parker Hannifin Corp., Pneumatic Div., Richland, Mich., (who is located in Trabuco Canyon, Calif.) described this automated equipment.

Modular fixture automates assembly project

A custom molder had a contract to provide molded covers for cellular telephones. When the customer asked the molder to add value to the project by assembling two connectors on each phone cover, the molder turned to Global Design & Procurement (GDP) for assistance. GDP's Fixture Direct Program combines standard design concepts and a family of modular components to built cost-effective, semi-automated tooling fixtures for low-volume and short-run production applications.

The phone-cover application called for the press-fit of gold-plated connectors into the cover in two places. Due to the odd geometry of the phone cover, attempts to produce the assembly manually proved difficult for the operator and the resulting cycle time was unacceptable. GDP's solution was to design assembly nests to hold the cover and connectors, then use a simple 3-axis pneumatically actuated press to hold the cover firmly while the connectors are put in place. The final fixture assembles three covers and their connectors in a single automatic cycle.

After the operator loads six connectors and three phone covers into the appropriate assembly nests, he or she manually actuates two anti-tie-down, zero-force optical switches. The machine sequence automatically commences. An air cylinder extends to close the press lid and hold the covers. A limit switch initiates the second step and three individual cylinders extend from below the assembly and insert/press three connectors into the bottoms of the covers. Another switch signals three more cylinders to extend from behind the assembly and insert/press three connectors into the rears of the covers. A fourth switch now commands all cylinders to retract and the operator can remove the three completed assemblies.

GDP has standardized on DIN-rail-mounted components. The three Parker Hannifin Telepneumatic solenoid-actuated 4-way air valves that run this assembly procedure stack on a rail, with each valve providing a manifolding port for the succeeding valve. The company also has developed a standard wiring and mounting recipe for the safety switches from Banner Industries, Minneapolis, that initiate a cycle. They mount in a Hoffman switch box through a standard 30-mm punched hole.

The fixture itself consists stock-size aluminum extrusions. The modular approach uses T-nut technology to assemble the frame and mount components onto it, avoiding intricate machining. (The stations actually have been re-configured a number of times to accommodate cover-design changes.)

Kevin Kordis, application engineer, Global Design & Procurement, North Andover, Mass., described this fixture.

Soft grippers take a seat - and install it

Assembly-machine manufacturer Solar Tool, Kansas City, needed a method to pick finished bench seats off pallets on a conveyor and move them into extended-cab trucks for installation. Limited space to maneuver in the cab was one design problem. Another special challenge for this equipment was to handle the seat without damaging the fabric upholstery.

The seats weigh only 100 lb, so pneumatic lift cylinders were appropriate, and Solar Tool found the answer to positive-but-gentle handling in AirPickers from Firestone Industrial Products Co., Carmel, Ind. AirPickers are soft-rubber-walled end effectors, designed to be inserted into cavities and then inflated to provide internal gripping force. They have no metal edges or claws in contact with the fabric and are more positive against the rough fabric surfaces than vacuum cups.

Solar Tool developed a scissors-like transfer mechanism with eight Model P055T AirPickers mounted on its fixture. When a seat arrives at the transfer station, the operator lowers the fixture (and its relaxed AirPickers) to surround the one-piece console-and-seat unit, with grippers at each end of the bench and in the spaces between the three seat cushions. After the fixture is positioned properly, the operator inflates the grippers to 60 psi. They expand to wedge around the seat and the fixture lifts it off the pallet. The operator now pivots and maneuvers the transfer mechanism to place the seat inside the cab, lowers the seat into its mounting position, and simply deflates the AirPickers to release it. With no moving parts and a very compact operating envelope, this final step is easily accomplished.

Designer Scott Wright of Solar Tool provided details about this equipment.

Air valves monitor conveyor activity

When material-handling systems for product distribution took off in the early 1980s, some of the conveyors in these integrated systems became huge - measuring miles in length and having multiple levels. A common problem with the conveyors occurred either when a container jammed and got stuck or when the container flow had to be stopped temporarily (to change trucks at the dock or to switch the containers to another line, for instance). When one of these events took place in an uncontrolled system, the drive motors would continue to send containers down the conveyor. They eventually collided with the stopped container and resulted in a pile up. Ultimately the accumulated horsepower of all the drive motors came to bear on the lead containers, often resulting in product damage.

Conveyor manufacturers developed accumulation or zero-pressure systems to deal with this problem. These automatic systems allow local control of container movement within a zone that typically is 18 to 24 in. long (roughly the length of a container). Several pneumatic circuits can achieve such local control.

If a container stops in zone A for any reason, its weight depresses a sensor roller (usually counterbalanced) that in turn releases the actuator of a sensor valve (typically a NC 3-way, in a 10- to 50-psi system). Venting this valve retracts a group of small diaphragm-type cylinders to release the clutches that drive the rollers in upstream zone B. With no power to the roller, the next container upstream will stop in zone B. This container then depresses the sensor roller in its zone and the sensor valve that is released will de-energize the drive clutches in upstream zone C to stop the drive rollers there. The process repeats for all upstream zones. Depending on zone spacing, this arrangement accumulates containers - holding and placing them at specific intervals.

(Obviously, containers also will depress the sensor rollers during normal motion, but the reaction time of the clutches is so sluggish that the container has passed and the sensor valve reset before the drive is affected.)

When the stoppage ends, the action reverses. The first container moves off its sensor roller, actuating the sensor valve and extending the diaphragm cylinders to re-engage the upstream drive clutches in zone B. When the container in B moves off its sensor roller, zone C becomes active, and the self-regulating process continues. Because the zones release only when the downstream zone is clear, an interval is created between containers.

In some circuits it is desirable to release or stop several zones at one time. To do this, the exhausts from the sensor valves involved are piped to a manifold. A solenoid valve, typically energized by the main control, can apply an overriding air signal through the manifold to pressurize the exhausts and stroke the clutch cylinders to engage the clutches in the zone group.

While this application does not appear to be complex on the surface, it has some subtle operating challenges for the air valves. For instance, the sensor rollers typically are positioned slightly above the level of the driven rollers - high enough to actuate the sensor-valve mechanism, yet low enough so as not to impede the containers. The weight of the container, sometimes much less than a pound, is the only force available to depress the roller and actuate the valve. This low force must overcome the positive counterbalance holding the roller in position, the friction of the mechanism, the friction and seal drag of the sensor valve, and the air pressure working on the valve parts - and do it without lubrication! (Most of these air systems are not lubricated because exhausting oil mist is unacceptable - especially in food-handling applications.)

To deal with low actuating force, we incorporate controlled and matched sealing elements in our conveyor valves to minimize stiction (the primary cause of inconsistent actuation). We test these valves mechanically with a 200-gram actuating force.

Reaction time of the valves is important. They must operate as repeatably as possible so the clutches engage and disengage reliably to maintain the correct container interval (intervals represent dead time which should be minimized). Also, the sensor valves have to exhaust quickly to assure fast clutch action in order to stop containers properly.

When viewed as an entire system, it becomes evident that the valves at the beginning of the conveyor line branch may actuate infrequently, but the valves at the end of the line may see thousands of cycles. It is common for the valve life-cycle requirement to be well into the millions of actuations. (Some valves we developed have been successfully tested by customers to more than 120 million cycles.)

Many times conveyor manufacturers are faced with unusual operating, installation, and environmental circumstances that require unique approaches to actuating these valves. In such cases, we have worked with them to design special devices that attach to valves as well as accessories. These have included: air pilots with integral orifices to soften actuation impact; over-travel actuators that actuate a standard valve at the top of its travel and continue for as much as an inch farther without damaging the mechanism; long cam arms (both straight and bent) to allow extra reach distance for actuation; and specially configured fittings, check valves, shuttle valves, and flow controls.

William P. Nugent, chief engineer, and Lori M. Fisa, marketing manager, Pneumadyne Inc., Plymouth, Minn., provided this discussion.