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Automating Water Jet Processes is a Smart Business Decision
by Bob Rochelle, Stäubli Robotics
Stäubli Robotics Posted 10/09/2012
1 WHAT IS FLEXIBLE AUTOMATION?
Flexible Automation systems are robot based automated industrial systems. By using a robot these systems Automating Water Jet Processes is a Smart Business Decisionare able to rapidly respond to process changes in response to market demands.
A prime example is a simple Palletizing system where bags, boxes or other containers of product are placed on wood pallets for shipment. This example was chosen because the principles of automation are relevant to many other processes and it is an easily recognized task in many manufacturing environments. There are three ways to palletize products in the industrial environment.
One method to palletize is manually. Manually means that people pick up the package of material within certain safe weight limitations and place them onto a wooden pallet for shipment. The people are trained to the create the layer pattern, stack to a required height and they also provide a level of Quality Control as they may see a defective package and can choose to eliminate it from theproduction stream. To provide flexibility, people can be re-trained. Thus new palletizing patterns or new heights can be created. To increase production speed, additional people can be added to the staff and conversely to reduce production, people can be eliminated or removed from the area.
Another method to palletize is with a Palletizing Machine. These machines mechanically create patterns of product and stack them onto the pallet. They utilize conveyors, guides, slide plates, droppers or other mechanical means to create and place products into patterns and build stacks of them onto a wooden pallet.
Flexibility in the system is provided by mechanical means such as changing or repositioning a conveyor guide, adjusting a pneumatic pusher or making change parts that must be installed. Changeover can only occur when the machine is off sizes are limited to the original machine specification. In some cases these machines are designed for a specific size package and as a means of providing high speed operation, they are not designed to vary from this ‘as designed’ package size and shape.
The third method to palletize is with a Flexible Automation System or a Robotic Cell. The robot is fit with a tool that is designed to pick up the product with grippers or vacuum or a combination and methods. These tools are designed to accommodate a large range of product sizes and weights without the need for mechanical changes.
The robot is programmed with a motion profile that picks up products from a given location generally on an in feed conveyor and to place them onto the pallet in a preprogrammed pattern and to a preprogrammed number of layers or stack height.
Flexibility is designed into the system because the robot tooling is designed to accommodate as many product sizes as specified by the process and the robot is programmed such that products are picked up and placed “on center”. Thus performing a product size change within a given system consists of merely repositioning center lines. No mechanical modifications or change parts are required. Additional flexibility can be built into the system by designing a tool that can pick up multiple products. In some cases tools are designed to handle bags, boxes, pails or overwrapped trays. Additionally they can be designed to pick up single or multiple parts This allows flexibility in that picking up two at a time can double production speed over one at a time and when placing on the pallet it allows flexibility in pattern creation.
For these robotic systems to function product must be fed into the system in a repeatable position and orientation. This is generally done on an in feed conveyor with a hard stop and sometimes the use of crowders are employed to maintain a consistent pick up location. In addition, the pallet must also be in a repeatable and positive location. Ancillary items like tier or slip sheets must also be automated and this can be accomplished via either the robot tooling or with a separate mechanism. Product size change in many systems is done manually by the operator making a selection on a control panel or it can be adjusted automatically if the product can be identified as it enters the cell or it can be via an input from an upstream machine or process.
For example, Bar Code readers or other means of sensing product may be used to accomplish this task. Stack height may also be entered by an operator or can be determined automatically by identification of the package being palletized. For a completely new products or unique pattern, the robot program itself may require modification. Today’s industrial robots all employ programming languages that have all matured to the point where this task is an easy one for trained personnel. Further, system builders can structure the robot programs with modules or sub routines that use variables thus making this task easier should it ever be required.
As a definition summary, Flexible Automation is the use of a robotic device to perform repetitive movements in industrial processes. The robot carries a tool designed to accomplish the task assigned to it. Spot welding guns, welding torches, bag handling tools, vacuum grippers, dispensing nozzles and water jet nozzles are example tools that can be attached to the robot arm to execute a motion profile or follow a path to the perform work. The program and the ability to modify it to suit any situation within the design criteria of the robot provides the ultimate in flexibility for today’s industrial processes. Robot based systems are the literal definition of a flexible automation system.
2 THE BUSINESS CASE FOR FLEXIBLE AUTOMATION
When considering business improvements, obvious areas of interest include reduction of direct labor cost, increase of product quality, increase in production speed and reduction of hazards to personnel in performing tasks. All these improvements are possible with flexible automation systems but the most compelling reason to automate lies in the operational cost savings when using a robotic system. To illustrate this, consider that the average cost for electricity to operate a 30Kg robot is about sixty cents (USD) per hour. If we assume a twenty year life span and a two shift per day operation, this means that the robot works for 80,000 hours and the power or labor cost is $48,000. Consider for estimation purposes that the life time maintenance is equal to the lifetime electricity cost which is a high figure for this activity. So, the total cost of operation for a 30 Kg robot to perform 80,000 hours of work is under $100,000. Now, let’s consider performing 80,000 hours or work at a burdened labor rate of $30.00 per hour. The total cost for this labor is $2,400,000. Of course there are costs to purchase capital equipment, install it, train employees and other costs but based on these numbers, we can surmise that using Flexible Automation to perform this work will save the client nearly $2,000,000 during this twenty year time. This is the business case for robotics.
3 FLEXIBLE AUTOMATION IN WATER JET APPLICATIONS
To apply flexible automation to water jet processes, remember that the heart of the system is a robot and the robot’s task is to move a device called a tool that performs the work required. In the case of Water Jet systems this tool would be the water jet nozzle. Or conversely, the tool could be a gripper and the part could be picked up by the robot and then the robot would move the part about the nozzle. Regardless the robot is the heart of the system and careful consideration should be given to the selection of this critical component. Following are descriptions of specifications for the equipment in a water jet flexible automation system. This paper will not address the water jet equipment but will cover in detail the rest of flexible automation system’s components.
Protection from the water and humidity is the most prominent issue that needs to be addressed in selection of the robot and the system’s ancillary equipment. Being an electric device, the intrusion of water into connections needs to be prevented. Seek a robot design that incorporates the connection point coming out the bottom of the base. This design should feature an O-ring seal at the robot base to provide a water tight seal to the mounting plate so no intrusion of water is possible to the connection point. In addition to a sealed base, a sealed arm design is paramount to prevent water intrusion into the mechanism. Covers over all motors, connectors, gear boxes or other components need to be sealed to prevent water intrusion.
A smooth arm design will allow run off of condensation and water plus it eliminate areas where water could collect in puddles or ponds and also allows for easy cleaning or drying if desired. A corrosion resistant coating and hardware is another requirement. This prevents bolts from rusting and the corrosion resistant coating maintains the robot arm in a new, rust free condition.
A final consideration in robot design is to use a purge system in the arm. Purging with low pressure compressed air will maintain a slight positive pressure inside the arm and further guarantee that water will not intrude into the robot.
In lieu of using a properly designed water resistant robot, some manufacturers recommend the use of covers. Covers can keep water from coming into contact with the robot but typically condensation occurs under these covers rendering a rusty mess of peeling paint after a number of years of operation. In addition the bolts and fasteners are exposed to this condensation making removal for service very difficult and more costly. Lastly, covers can leak through a rip or it is possible that they are just not installed or are not installed properly and the robot is then exposed to the water. In any event it would be prudent to employ a robot specifically designed for the environment it is intended to work in.
System and Robot Controls can be in purged or water tight cabinets but a better option would be mount the controls in a location remote from immediate water exposure hazard.
A further criterion in the selection of robot equipment in a water jet system is similar to any industrial process. Robots are rated in payload and reach.
The payload is the maximum allowable weight that the robot arm is designed to carry. In the case of a Water Jet system, this would be the weight of the nozzle apparatus plus the mounting means to the robot. Further consideration needs to be made for the back pressure as a weigh that is imposed onto the robot arm.
Typical robot payloads are ratings for mounting to the tool mounting plate at the end of the arm but there is a second specification for the robot arm that dictates the maximum payload for the arm itself. In water jet systems there is the possibility that the arm will be required to carry water delivery hoses or other cabling. If this rating is exceeded then these items can be wall or ceiling mounted to hold the weigh yet be flexible enough to move as needed by the robot’s motion.
Sizing a robot for payload is a straight forward exercise in that the allowable robot payload should not be exceeded by the weigh equivalent of the developed force plus the weight of the tool plus the cabling and water hoses.
A final note on payload is that there is an inertial rating for a robot and this criterion needs to be checked for proper sizing. In water jet applications due to the low weight of the nozzle this ought not be exceeded but a careful examination of this loading would be a prudent step in selecting a robot.
The robot reach is the area in which the robot can effectively work. In six axis robots this is generally a global shape. In other robot designs this is more of a rectangular solid shape since the wrist is not part of this design. Where the water jet originates is the point where the work is performed so this is the point that must be moved to accomplish any work. If the part being processed is of an irregular shape and the process requires that the robot reach around or over some of the part geometry this needs to be considered in the robot size selection.
Depending upon how the nozzle is mounted to the robot arm, it may extend beyond the robot arm. In this configuration the amount that the nozzle exceeds the range of motion of the robot arm alone needs to be added to the robot reach. This effectively extends the robot’s range of motion or reach. Note that all robot manufacturers and most system integrator will run a software simulation of the system design to verify that the robot selected is capable of reaching wherever it is required to. This simulation can also evaluate various mounting locations thus enhancing the system design for maximum efficiency.
Besides the robot mechanism and the water jet equipment the flexible automation system includes ancillary equipment. This additional equipment should be selected carefully to survive in the wet environment of a water jet system. These additional components include but are not limited to control system components such as sensors. Part present and location sensors are paramount to a successful process. The system control needs to know that a part is present and more precisely if it is not in a repeatable and positive fixtures then we need to know where it is so that motion can be automatically adjusted to accommodate this alternate location. Sensors can be employed to verify part geometry or provide inspection prior to or after processing. Prior inspection and detection of a bad part means that that part can be rejected and not processed. Inspection after processing is a means of verifying that the system is operating as expected. Proximity sensors, photo eyes, finger switches and vision systems can be employed to perform any of these sensory feedbacks in the water jet system. Note that all sensors must of a water proof design and wired in accordance with wet environment standards.
Considerations must be made in system design to introduce the parts into the cell for processing and to remove the finished parts. Depending upon part geometry, this can be accomplished in a variety of ways. Conveyors either over head or other styles can present parts, operators can load fixtures or material handling systems including other robots can perform these functions. Realizing that the robot is a repeatable device, these fixtures and the part transfers must be of a positive nature so that there is no possibility that the part is being presented to the robot in any fashion except the way in which the robot expects it. The use of part fixtures that are keyed for location is recommended and the use of part present sensors to verify that the part is the correct one and placed correctly before processing begins needs to be considered. If parts are travelling and must be processed while in motion the use of a Tracking function will allow this. In tracking, sensors are necessary to determine an initial location to initiate tracking and a feedback of conveyor speed is necessary to maintain location.
Cell Safety must also be considered. The installed system needs to conform to the most current applicable Safety standard. The North American Robotic Industry Safety Standard is administrated by the (RIA) Robotics Industry Association (www.robotics.org). This standard requires personnel protection such as enclosing the robot in fencing or other means to prevent accidental access to the system. Interlocked doors are a requirement and this means that consideration must be given to parts coming into and leaving the cell. In North America, all robots sold are in compliance with the RIA Safety Standards. And all reputable System Builders will design a system that conforms to the requirements of the RIA Safety Standards. It is incumbent upon the End User to train their employees in safe operation and to maintain the system safety equipment as designed to prevent accidents.
In many water jet systems, a booth or enclosure is used to further isolate the water jet environment from the rest of the plant. Consideration must be made to the design of this structure to allow for freedom of robot movement, parts movement and maintenance access to the entire system. This structure also functions to further isolate the control systems from the wet environment.
4 FLEXIBLE AUTOMATION SYSTEMS IN WATER JET APPLICATIONS
With the above definitions, justifications and issues related to the use of robotics in Water Jet Applications, the following are some illustrations of the applications this technology to various industries
These are examples of multi axis systems that typical employ a six axis robot. Six Axis Robot motion is defined by the mechanical joint that produces the motion. Joint 1 is rotation left to right, Joint 2 is movement back and forth, Joint 3 is up and down, Joint 4 is a roll which moves from horizontal to vertical, Joint 5 is a Wrist like motion and Joint 6 is tool rotation. The maximum angles used are dependent upon the water jet nozzle but the robot provides this overall flexibility in the system. It opens up a wide range of possible applications that cannot be processed on other systems.
The ability to provide angles in the water jet can be useful for applications like weld preparation where a bevel angle needs to be cut on all sides of a part that will later be welded. For taper compensation, the kerf angle can be transferred to the waste material thus eliminating the taper commonly found on water jet-cut parts. All this can be accomplished with the flexible automation system applied to a water jet system.
The following is a brief list of some industries and applications where robots exist in Water Jet Systems.
Many materials used in aerospace manufacturing are well-suited for water jet like titanium, zirconium, aluminum, brass and others. The complex shapes required with the thigh quality standards dictate the need for accuracy. The repeatable, accurate nature of the six axis robot with a water jet system provides this in a flexible package.
Water jet robots are commonly used to cut car interiors parts such as door trims, headliners and carpets. Metal components such as floor pans and body panels are also candidates. In the Automotive industry the philosophy is to create a standard platform and do many of these to gain the economy of scale. Modifications to this standard are required to produce the options that the market demands. For example the standard vehicle floor is stamped for the use of an Automatic Transmission. When the build menu requires a Manual Transmission then a water jet system is used to modify the standard floor to add holes for clutch pedal linkage and the manual gear box shifter. Likewise for a sun roof, body cladding, rear deck spoilers or other items, water jet cuts to the standard body panel are employed..
Floor tiles for commercial buildings can be cut with a water jet system to create mosaics, patterns or scenes in a building’s floor. The flexibility of the robot based water jet system gives the artist designing the floor a freedom of expression that was limited by hand cutting in the past. And the accuracy and clean cuts by this system greatly ease the installer’s job at the building site. Other items like the guide rails for household garage doors are processed with robotic based water jet systems. As these guides are extruded the robot systems cut the holes required for the door latches while the part is in motion. This has increased the production time over setting up and stamping or drilling these holes.
Circuit boards, insulation, plastic covers and housings can all be cut or trimmed using water jets systems and robots. The important characteristic in this application is that the parts be accurate, clean, dustless and the quantity is generally very high. A water jet coupled with a robot provides the required accuracy, speed and repeatability in a non-damaging, low heat environment to process these parts.
Water jets provide a clean, effective way to cut food products like cheese blocks, trimming meat or removing shellfish attached to growth media. The water can be a clean or sterile medium thus diminishing the chance for contamination of the product.
Water jets are ideal for cutting through multiple layers of fabric. Items such as hygiene products, diapers, carpets, fabrics, insulation material and others are candidates for water jet processing using robots. The articulation of a robot with a water jet will yield the lowest cost method of providing the unique shapes required by market demand.
4.7 RECREATIONAL VEHICLES
Jet Ski covers and Boat hulls are examples of routine candidates for processing with robotic based water jet systems. These parts can be trimmed and de-burred then accurate holes can be placed in them for mounting additional items such as deck rails or other parts. Previously holes were drilled and saw cut an misalignment was a constant problem. These misaligned holes were an issue if parts replacement was required as field service plus part misalignment in these holes was a cause of leaking. The accuracy of the robot mounted water jet system has provided accurate and repeatable hole placement An ancillary benefit to this is that these manufacturers can now adopt the Automotive Model of building a standard and then these customer driven modifications to an order becomes an easier task to handle.