Apackaging operation typically uses many types of conveying, sensing, and control equipment. The motion system that controls this application must interface with all of this equipment, easily adapt to various control schemes and changes, as well as start, stop, and adjust the speed of a production line during the various operations.
The House of Seagram recently built a new bottling and distribution facility. The engineers needed drives that would meet these criteria as well as precisely coordinate and control the speeds of numerous conveyors, for without such precise control, wasted or damaged product would become the norm.
The plant in Relay, Maryland, (south of Baltimore), bottles 18 million gallons of beverage alcohol a year — from various brands of blended whiskey, scotch, flavored rum, gin, to cordials. Conveyors carrying the bottles move at different speeds during cleaning, filling, and capping operations, and when the conveyor lines split or merge. The line speed ranges from 180 to 220 bottles per minute.
Without a precise motion system control, bottlenecks can occur when the conveyor lines merge. There, the distance between bottles shrinks, sometimes to zero. When this happens, the bottles butt against each other, building “back pressure.” If not relieved, the pressure grows until it is strong enough to break the bottles, spilling the product onto the plant floor.
Even if the back pressure doesn’t build to the point of breaking the bottles, it can still damage the product. Specifically, the pressure from squeezed bottles can damage the identifying labels, which is a significant quality issue for an industry that relies on brand recognition. Marketing demands meticulous care of the label. Unlike other examples of consumer product packaging, a bottle of whiskey or other liquor stays on the shelf longer — in homes, restaurants, or bars — and serves as a standing advertisement. “Therefore, we particularly want to avoid the chafing, tearing, or smudging that can result from bottles pressing too closely together on a conveyor line,” says Mike Brown, packaging engineer, the House of Seagram.
Coordinating the line
Empty bottles are un-cased and set on the conveyor, Figure 1. They are then cleaned and filled with the liquor. Throughout the conveying system, an electronic eye measures the distance between bottles. It sends a signal to a programmable controller (PLC) indicating how many bottles are moving in a specific time. The PLC uses this information to send signals to inverters to constantly adjust the speed of the conveyors as the bottles merge and separate.
After filling, the bottles move to the fill-level check station. Using a PID algorithm, a PLC sends a signal to an inverter, which then starts and drives the vacuum-blower. The vacuum-blower sucks excess product from bottles. A vacuum transducer sends an analog signal back to the PLC. Based on PID calculations of that signal, the PLC tells the inverter to maintain the vacuum at the proper level.
Then the bottles move to accumulation areas, moving around until they eventually go onto a conveyor that takes them to the labeler. Once labeled, the conveyor splits into two areas for packing.
One inverter used four ways
The engineers at the plant chose the E-trAC WFC Series ac inverter, from TB Wood’s Inc., Chambersburg, Pa, for the motion control system. Says Mr. Brown, “We chose these for their compact size, ability to interface with any type of shaft encoder, ability to adapt to our control schemes — for example, we use RS 485 for device communications — and for the option of adding plug-in cards for other features we may need. We also liked its documentation, which was easy for us to use to set up the inverters.”
Initially, 20 inverters were purchased, Figure 2, ranging from 1 hp to 15 hp. Later, 20 more, of varying sizes, were added.
In a NEMA 4 enclosure and with a small footprint (the 5-hp inverter measures 12 in. x 9 in. x 5.5 in.) the inverters control over 80 parameters, including frequency range, starting torque, acceleration and deceleration, and torque limit and boost. Top frequency of the inverters in this application is 120 Hz.
Seventeen of the inverters are concentrated in one area of the bottling plant. Within this group is a bank of 15, 1-hp drives, says Scott Popiolek, electrical controls engineer. These control and vary conveyor speeds. If the inverters run at a fast speed, bottles have more space between them on the conveyor. If the inverters slow the speed, space decreases between the bottles.
A vertically mounted 10-hp inverter controls the vacuum-blower. A 15-hp vertically mounted inverter drives a frontend line shaft that turns cleaner, filler, and capper lines. The other inverters are used to control any other adjustable speed application on the line. The inverters are used in four control schemes:
• The ones controlling the conveyors receive a digital signal from a PLC. The signal tells the inverter to start, ramp to prescribed speed, or stop the bottle conveyors.
• They receive analog signals from the PLC to adjust individual conveyor speed based on signals the PLC receives from the electronic eyes.
• They communicate to the PLC through an RS-485 based serial input/output link (SIO) to control the conveyors, Figure 3.
• The inverters receive PID signals from the PLC to control the speed of vacuum pumps.
In addition, Mr. Popiolek notes other product benefits, such as diagnostics. “We have the inverters programmed to let us monitor parameters such as amperes, volts and temperature, for troubleshooting. If the motor runs hot, we can check to see if it’s drawing too many amperes, for example.”
The same signal that starts a motor starter can start the drive.
With the inverters and an ongoing company- wide quality program, the bottling operation has reduced the label defects — the smudges, imprints, and wrinkles — and nary a drop has been spilled.