by Micah Swett, sales manager, Diversified Printing Techniques
Factory automation is quickly becoming more commonplace in today’s manufacturing sector. With labor shortages, a decline in experience levels and rising wages, factories want to automate the pad printing process to ensure the work gets done even when qualified workers are in short supply. Unfortunately, most companies are not doing this, for technical and commercial reasons.
Pad printing machines have evolved into complex pieces of equipment, with precision movements controlled by guide rails and servo motors. However, historically most pad printing machines have been loaded by an operator who feeds the parts into the machine and takes them out at the end of the print cycle.
Automation with robots
Pad printing can be more challenging to automate than other processes due to the diversity of products that can be run on one machine and the sensitivity of the inks to the process. One consequence is that pad printing lags in the automation of loading parts into a printer. Many companies have developed high-level machines with vision systems, rotating fixtures, high-speed movements, auto unload, etc but the system is still loaded by an operator. This operation often uses more than just the loading operator because someone must bring raw goods to the machine, take finished goods away from the machine, and tend to the inks and other needs of the printing equipment.
It takes little imagination to realize that one operator can run a cell like this if the material were automatically loaded and unloaded from the print system. A common answer for this is feeder bowl technology. Feeder bowls can be a good solution for this type of situation; however, this is a large investment and it is dedicated to one product. Most managers are looking for more diversity in their solutions and want to be able to change things later, making a feeder bowl a limited solution.
Robot technology can automate the loading of the work cell and provide a flexible solution. A robot can be set up with memory and be used to perform many different tasks when the proper job is recalled from the memory. The capital cost is still there, but the dedicated solution becomes a diverse solution that can be utilized for many different projects.
“Pad printing automation is not just buying a robot,” explained David Ho, president of Kent International. “Two automation factors must work together to form complete automation of the pad printing process: automated pad printing elements and robotic elements.”
Part delivery to the robot
It is important to determine the method by which the parts will be delivered to the robot. There are several ways of doing this. One method is to bring the parts to a robot on a conveyor, which can be fed by a hopper, human hand or injection molding machine. If the parts are randomly placed on the conveyor, a vision system can be used to tell the robot which of the parts on the conveyor it can pick and what the robot should do with the parts to properly orient them for pad printing. If the parts cannot be used by the robot, they can be recycled by the feeding system until they can be used.
If the parts are generally placed onto the conveyor in the correct orientation and in a repeatable fashion, simple tooling can be used to position the parts for the robot to pick off the conveyor. In this case, no vision system is needed for the feeding. Once the parts hit an end stop tool or escapement mechanism, a signal tells the robot to pick up the parts and put them on the pad printing machine.
Trays are another method to get parts to a robot. The benefit of a tray is that the parts will always be in the same pattern. The robot can be taught what the pattern is and then can work in a repeated program to unload the parts from the tray to the printer. The robot can then refill the tray with the printed parts. This allows for a smaller footprint and a simple operation.
The trays can be loaded by hand, which still saves labor due to the simple work and speed at which this can be done. The tray also can be loaded by equipment, such as an injection molding unload robot or other assembly equipment. The trays can then be sent on to other processes or just unloaded and reloaded. The trays can be fed to the robot on a conveyor or in a stacker.
A common stacking method is to use a stack-up tool, which takes a certain number of trays and holds them in a vertical queue. Once the top tray is unloaded, printed and reloaded, the robot moves the tray to another destination. The next tray in the queue then indexes to the top, and the robot begins to work with these fresh parts. The completed trays can move down a conveyor to another process or pack-out station. Alternately, the tracks can move to a stack-down unit where the trays wait in queue to be unloaded by an operator.
Types of robots for pad printing systems
Typically, three types of robots are used for loading and unloading pad printing systems. The most advanced design is a 6-axis robot. The 6-axis robot is the most similar to a humans movement. It is flexible, with six joints that are arranged in chain so that one joint supports the next joint further down the chain. The 6-axis robot is used when a part must be turned from one surface to another for proper printing. The 6-axis robot can be integrated to work with most conveyor and tray feeding solutions; however, it can be complicated to program. A 6-axis robot also provides greater versatility and range than other robots.
A SCARA robot is very common in the manufacturing world and is used in many applications. It is a lower cost solution than the 6-axis and has four axis points of movement. The SCARA has two parallel x and y axis points, a rotary axis and a Z (up/down) axis. A SCARA robot can usually be integrated to work with most conveyor and tray feeding solutions and is less complicated to program.
A gantry robot is very simple and is used in many pad printing systems today, usually for unloading operations. A gantry robot is equipped with cylinders built together to allow a gripper or suction cup to move in and out with a simple up and down movement. A gantry robot is limited, only able to operate in a 2D rectangular space. A gantry is known for pick-and-place, meaning it can pick up a part from position A and move it to position B. This can work with a feeding conveyor that has a fixed position tool. Otherwise, it is not technical enough for feeding.
Pad printing process modifications
With all the technical advancements in automation and robotics, operators still must deal with the mystery of pad printing. Fortunately, some pad printing equipment manufacturers have taken steps to improve the process. Through technological and practical improvements, pad printing equipment has reached a point where it can be placed in an automated cell and be expected to perform with repeatable results. There are two crucial items needed to provide an automated pad printing cell: tape clean and automatic viscosity control.
If a machine cannot clean the pad automatically, there is risk of carrying contamination from the part back to the cliché. This will cause future prints to have imperfections. Also, tape clean removes any extra ink off the pad, allowing for a clean printing surface. Keeping consistent viscosity is crucial to running an automated pad print cell. Some equipment has the capability to add thinner to the ink, using an algorithm based on the size of the ink batch, type of plate and speed of printing. With a consistent viscosity, an automated cell can run much longer without the ink needing to be modified.
Adding a vision system to a robot-loaded pad printing system is like adding insurance. With a vision system, the printing can be monitored to ensure quality parts are produced each cycle. When having a robot unload the parts, parts that fail the vision inspection can have an alternate destination to keep them separate from those that pass inspection. Many times, an automated system will have a program to allow only so many failed prints in a period before stopping. This would give an operator the ability to make an adjustment to correct the issue before continuing.
Benefits of robotics in pad printing
Using robots for pad printing automation will reduce labor needs. This allows operators to be available for other tasks or to become trained for higher skill-level jobs. Using less labor during the production process will reduce the overall costs for pad printing as well. However, using robot automation has other positive effects for production. It breaks the link between the operator and the cycle of the printer, which allows an operator to pause for any reason (get another box of parts, answer a question, etc ) and not stop production.
The consistent production cycle that robot automation gives will improve throughput. Having a consistent machine cycle also is good for the pad printing process. The inks behave consistently when they are used in a more repeatable manner, providing more quality prints in less time.
It is important to use the right pad printing equipment when integrating it with robot automation. Work closely with machinery manufacturers to make sure the equipment has features that simplify the pad printing process, such as auto viscosity controls and tape clean. Discuss the need for vision inspection systems, and determine the correct feeder technology for the parts being printed with the manufacturer’s input. By adding robotic automation to pad printing, companies can reduce labor, increase repeatability and remove unnecessary touches from the process.
Micah Swett is the sales manager for Diversified Printing Techniques. Diversified is the exclusive agent for the US for Kent International, which offers a unique advantage to those companies wanting to add automation to pad printing operations. Kent has been providing pad printing solutions for decades. However, the company now is designing and building its own robots specifically for pad printing. This allows for great solutions which are made simple for pad printing applications. For more information, call 704.583.9433 or visit www.diverprint.com.