In the world of automation, it’s easy to get caught up in the capital projects. When you mention motion, most people will immediately create a mental image of a machine or process with multiple axes of coordinated motion and complexity.
Lurking close by would be a programmable logic controller (PLC) or programmable automation controller (PAC) with lots of horsepower and connectivity, or, perhaps, the processor is embedded in the motion platform itself. Those big-money events tend to draw a lot of attention, and rightfully so, but, for a guy like me, it’s the smaller projects, down in the trenches, that are the most fun.
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We ran into such a scenario not too long ago. My employer was setting up a new production line. There was a lot of money involved with new-to-us vendors and technology. It’s been a bit of a journey, but our team has finally embraced servo technology, and we are reaping the benefits. As often happens with our projects, the usable workspace isn’t always ideal, and we have to get creative when it comes to putting it all together.
As a co-packer, we would traditionally just throw people at a challenge and do whatever we need to do to make product. With a fully automated line, we don’t have that option.
For this particular line, we needed to be able to erect cases, automatically, that could be left- or right-hand-oriented opening. This wouldn’t be an issue if we had people opening the cases, but to do this using automation was, as it turned out, a formidable challenge. In fact, for the case speeds we were facing, we were only able to find one vendor who produced a machine capable of doing this.
The challenge for us was how to fit that machine into our packaging line. As it turned out, we couldn’t. This wasn’t the end of the story, however. For the first time in our history, we decided to locate the case erector on the floor above packaging and send the cases down to the floor below. Our approach was to install a stainless-steel chute to transition the now-erected cases down to the case packer on the first level.
Now, for anyone who has worked with gravity before, there is quite a challenge to create a steep enough angle to allow for the free flow of product while not having that product launch when it hits terminal velocity.
We didn’t have a lot of horizontal distance to provide a gradual slow down section to the horizontal plane. We also had to ensure that the empty cases didn’t just stall on the deceleration section and not make it to the case packer infeed.
Our solution was to provide a means to both slow down the cases and power them onto the infeed of the case-packing machine. The concept was to mount a soft wheel on the side of the chute that had a bit of compressibility to its construction. We toyed with controlling this with a variable-frequency drive but, ultimately, elected to use a stand-alone servo motor with built-in drive.
Stand-alone drive/motor combinations have been around for a while, so it’s not necessarily a new technology, but what made this particular decision easier for us is the availability of smaller, fractional horsepower solutions in this integrated package platform.
Our case packer would simply send a digital signal to indicate when the infeed belt was calling for more cases, and our metering system would cycle on and off to match. Since we now had a way to both hold back product and positively index individual cases out when we needed them, it was the perfect solution to our challenge. Servos have a lot of torque, and this gave us another advantage, in that we could use the vertical section of our chute to accumulate product and, using a photo eye, cycle the conveyor at the top of the chute to keep that accumulated section full of product.
The result is that the drop section, once the accumulated section was loaded, was shortened from 14 feet down to only 5 feet. The cases don’t even come close to meeting terminal velocity, so the transition is gentle with very little bounce back from empty cases colliding.
Motion doesn’t always mean big solutions, but sometimes it does. One of the more entertaining things that I get to do in my current position is give life to older machinery—for example, a machine that automatically dispenses cups used for microwavable products and then cycles those cups through filling and sealing stations before ejecting the finished product out onto a takeaway conveyor for further packaging.
When we first got into this type of business, we purchased a piece of used machinery with the thought that we would give this a try, and, if it wasn’t for us, then we weren’t out much of an investment. Well, we soon discovered that, while the machine came with a control system, it was older technology, and we needed to give it an upgrade to something newer.
This particular machine was completely mechanical in nature. The main drive was an indexing gear box with various pneumatic devices operating the cup dispenser, sealing and cup-eject stations.
We started with an older PLC platform, and that worked for us for the first year or so of operation. We started to get a little more sophisticated, especially with the peripheral devices and set upon a goal of eventually replacing some of the mechanically cammed operations with servo versions. While we didn’t immediately jump into a servo system, we did recognize that our older PLC platform wouldn’t allow us to add a servo system. The first step in our journey was to replace that older PLC with a modern programmable automation controller (PAC) with motion capabilities.
The hardest part of the upgrade was converting the PLC application into the newer processor. We reassigned the human-machine interface (HMI) tags to mate up with the new processor and spent some time to completely re-commission the PAC and HMI off-line to make sure we were ready to go. The actual PLC swap out took less than two eight-hour days, and we were back in business.
The next step took a little longer than we had planned. In fact, we ended up hiring an independent machine builder to make us a similar machine, with learnings from our first experiences at cup filling/sealing.
The new machine included the same processor and HMI as our first machine so that we could include it in our plans for a fully operational servo machine. Included in this newer model was a servo main cycle drive with indexing capabilities to match the mechanical version on the first. It’s important to mention here that not all journeys need to be fully immersed. Sometimes, it’s better to just get one’s feet wet and figure out the process as you become more comfortable with it.
With cup-filling machine versions 1.0 and 1.5 in operation, we were excited to get on with the next part of the journey and started the process of converting the air-operated seal heads to servo operation. We decided to do this operation next because the most important part of the whole machine is to properly seal the film to the top of the cup.
Sealing is dependent on two very important parameters—time and pressure. If either one is off, the seals are not sufficient. With a pneumatically operated plunge, we were limited by the distance of the stroke on the cylinder and how much dwell time we had while the head was in contact with the cup. We were limited on how fast the machine could run because the two critical elements, time and pressure, were fixed due to the pneumatic operation. It was clear that servo motion, cammed to the main cycle shaft, would give us the flexibility to make good seals and increase the overall speed of the machine.
On our pneumatic version, film could easily melt if we located the stroke too close on a machine pause, so the original machine builder had a long stroke on the cylinder. Keeping the seal head farther away from the seal position adds extra time in the cycle that can’t be altered. The great thing about servo motion is we can break the functions up into different strokes, depending on where the machine is in the cycle.
At a full machine reset, the seal heads are positioned far above the sealing surface to allow for manual functions like threading the film through the machine and clearing machine jams. Upon resumption of cycle, the head can be advanced down to a dwell position that is just high enough to prevent damage to the film. Seal cycle times are significantly shortened, and we get the bonus of the torque that a servo can apply to the stop position. The two key elements are accomplished—time in the seal position and pressure on the film on top of the cup.
As it happens, we ended up buying yet a third machine from our machine-building partner before we got a chance to implement the changes to our version 1.5 machine.
Happily, we felt confident enough with our trials with that machine that we worked with our vendor to go full servo on the third machine by adding not just the sealing operation, but the cup-dispensing and cup-eject stations, as well. The great part about this collaboration is we can make these same changes to our first servo machine and end up with two great machines for our efforts. At some point, we can also go back to our original machine and bring it along on the journey.
Servo need not be a scary journey. Take little steps, get comfortable with the process and take bigger steps when you are ready. Don’t be afraid to experiment. As we experienced with our empty case indexing wheel, there are plenty of applications that can benefit from technology without spending a lot of money.
