Modern Pad Printing Technology
by John Kaverman, president
Pad Print Pros LLC
The benefits of pad printing machines with all-electric, programmable, stepper motor drives alone provide lots of reasons to move away from pneumatics.
Pad printing technology advances have led to efficiencies in energy, maintenance and cycle time.
All pad printing machines are not created equal. At first glance, they all appear to be doing the same thing, but internally there are major differences when it comes to the level of technology employed to make them operate.
I think you would agree that if everyone reading this article were sitting in an auditorium listening to me present this in person, and I asked you all to take your cellphones out and hold them up over your heads, at least 95 percent of the audience would have a smartphone that is less than three years old. Yes?
Strangely, I am contacted almost daily by companies that somehow expect to obtain 21st century results while using pad printing technology that, in phone terms, represents a level of technology equivalent to an old rotary phone with a long, twisty cord. The benefits of all-electric, programmable, stepper motor drives alone provide lots of reasons to move away from pneumatics.
Single plug simplicity
Start with the simplicity of a single plug. If you have clean electricity, you can run the equipment. There is no need to plumb in air. This makes the machine substantially more mobile, so that as production demands change, you can move your machine to where it is most needed.
Preventive maintenance on stepper motor-driven machines is nearly eliminated. Without cylinders and their associated issues, the equipment requires very little care. There is no worry about filters, water or oil in the lines, seal failures, gummed-up valve banks, etc. All you have is periodic lubrication of the cams, followers and linear guideways. Simple.
Stepper motor-driven machines are quieter than pneumatics. Compressed air is a substantial contributor to the overall noise pollution of your shop floor. Quiet, electric drives keep the dB rating low.
Better energy efficiency
Electric machines are less expensive to operate and maintain than older machines. The use of pneumatics to drive motion in equipment is practical and convenient at first glance, but it also can be expensive. Running an air compressor requires an enormous amount of electricity in comparison to the power output. Air compressor efficiency is the ratio of energy input to energy output. Many air compressors may be running at efficiencies as low as 10 or 15 percent.
The average cost for electricity in the United States as of October 2016 was $0.1027 per kW hour. This example utilizes a specific (German) 90mm pneumatic printer, but any 90mm one-color pneumatic pad printer will run with about the same usage or worse.
If the machine is working at an average rate of 1,000 cycles per hour, it will require 2.7NL per cycle and 2700NL per hour at 90PSI. This is equivalent to about 950 cubic feet per hour, or 16 cubic feet per minute. It takes approximately 0.25 horsepower to generate 1CFM; it takes approximately .207kW per hour to generate the necessary horsepower to generate 1 CFM. So, it will take 3.1kW to power a printer that requires 16CFM.
With a national energy cost of $0.1027, that equals $636.74 in electricity per shift per year, if the compressor is 100 percent efficient ($0.1027 x 3.1kW x 2,000 hours).
The equivalent stepper motor-driven machine uses 500 watts total per hour when running ($0.1027 x 0.5kW x 2,000 hours = $102.70).
Im sure you can do the math, but this is a $534.04 savings per shift per year on our smallest piece of equipment, if the air delivery system is 100 percent efficient. Throw in the general maintenance on the compressor and consider the reality that there is no way the compressor and air delivery system is running at 100 percent efficiency, and youre probably saving closer to $1,000 per shift running our 100 percent electric equipment.
Superior process control
If the stepper motor is the heart of the machine, the controller is obviously the brain. While the limited controls behind a pneumatic machine largely have gone unchanged for 50 years, 30-plus years of continuous development, field testing and improvements have allowed the manufacturers of stepper motor-driven machines to offer to the most advanced controls package in the pad printing world, with a sustainable and stable upgrade path for every machine built.
Stepper motor-driven machines use proprietary controls and software to run the printer and conveying accessories simultaneously. This is truly out of necessity since off-the-shelf programmable logic controllers are too expensive, cumbersome and slow for this modular equipment. These control systems allow stepper motor-driven machines to be easily paired with programmable, stepper motor-driven, plug and play accessories, such as linear indexers, rotary tables, pad shuttles and more.
Stepper motors allow for complete control of the cycle through the keyboard of the machine, without extensive training. This is unheard of on competitive equipment and is a function of the stepper motor drive and proprietary software. Included on most stepper motor-driven machines are controls, such as those listed here.
Independent speed control in every axis of motion. There are six motions in every pad printing cycle:
- doctoring forward
- doctoring backward
- pad down over plate
- pad up over plate
- pad down over part
- pad up over part
If youve pad printed, you know how critical these speeds are to a quality print. This being the case, why do many manufacturers ignore these controls or put them out of reach of the operator? With stepper motors, these important parameters easily are changed with the push of a button. No flow controls or tools are required.
Independent delays/timers in every axis of motion. Why slow down the overall cycle when all you need is a one-tenth delay to allow the ink to tack off before printing? What if you want to pause on the part for 0.25 second to allow the pad to conform to a difficult texture? With a stepper motor, you can program delays before ink pickup, on the cliché, before print and on the part. Independent stroke adjustment in 1mm increments over the cliché and part. Have you been using limit switches and knobs to adjust your strokes? Does your machine have no adjustment at all? Why not just tell it where you want it to go? With a stepper motor-driven machine, if you need 1mm more or less compression, you push a button and youre there.
Training mode. When setting up your machine for a new application, most stepper motor software gives you the flexibility to walk the machine through the cycle. By holding a button, you can slowly jog the machine into position, hit enter, and the machine learns the stroke. Training mode allows you to quickly set up a new program (which can be stored to memory) in seconds.
Stepping mode. All motions of the machine can be run independently when the machine is put into stepping mode. Isolate doctoring, pad stroke or indexing so you can see exactly what your machine is doing. This can be run at full speed or in incremental steps, greatly reducing the time necessary to troubleshoot image quality-related problems.
Multi-program memory. All of the cycle parameters mentioned previously can be stored in the memory of the machine for immediate recall, minimizing changeover-related downtime.
Easy automation. Stepper motor-driven machines are easy to automate. If you are using their plug and play conveyors, you can mount the accessory, add the necessary driver card and call up the program that is pre-loaded into the controls package. If you wish to integrate the equipment with your line, all the necessary inputs and outputs are present for communication with external programmable logic computers.
Built-in upgrade path
One of the key advantages to most stepper motor-driven machines is a viable upgrade path for every machine in the field, within the limits of its size. In modern US manufacturing, production requirements change constantly. Today, a tabletop machine with a two-position indexer might suit your needs exactly. In a month, you could need a high-speed rotary table. Rather than having to go to a third-party vendor for conveying accessories and PLCs, a plan is already in place.
Most stepper motor-driven machines come with built-in controls for a range of plug and play conveyors and part position devices. In most cases, the end user can reconfigure the machine without having to send it back to the manufacturer.
I can promise you this: All pad printers are not the same. Stepper motor-driven machines make many impossible print jobs possible, marginal print jobs standard and easy jobs serious money makers.
I believe it is critical when you make a final decision on upgrading your pad printing equipment that you consider not just the sticker price but the real bottom line production cost for parts. If youre committed to manufacturing in the US, you know that a zealous commitment to efficiency, speed and precision is your only chance at fending off the competition. In todays global economy, youll probably pay your workers more than most overseas manufacturers. I strongly suggest that you level the playing field by providing them with the best tools for the job instead of continuing to struggle with antiquated technology.
Expand your capability and capacity for new applications, increase your real output, decrease your setup times and watch your margins improve. Isnt this what real productivity is all about?