Motion Control Resources
Ward/Kraft Sees Future in Servo Technology
Siemens Industry, Inc. Posted 08/28/2006
Siemens Totally Integrated Automation Part of the Plan
Ward/Kraft, Inc., is a private, nationally known manufacturer of business forms / labels and documents. Five years ago, the company conducted a cost benefit analysis comparing line shafted and servo driven machines. It found that over time the investment in servo technology would pay off in faster production times, less waste and fewer mechanical repairs. Ward/Kraft also found a partner in Siemens Energy and Automation that supplied what the company refers to as a “Totally Integrated Automation” approach to its business.
“From day one, the plan calls for designing and building all our machinery in house and installing servo systems on any machine we create,” said Steve Adamson, Ward/Kraft electrical engineer. “The technology is there. The support is there. But, we’ve had to build that confidence level over a period of years.”
The plan is working. Established in 1972 in Fort Scott, Kan., the company has doubled in size over the past 10 years. According to Adamson the key to this success is a top management willingness to invest in the future, especially in its machinery division.
“Most companies our size will not make the upfront $1 or $2 million investment in an in-house machinery division.” Adamson said.” And then the question comes up; can we staff it with good people to maintain the system? Ward/ Kraft is unique within the independent printing industry. Few competitors our size company can do this. That gives us a competitive edge by lowering overall costs up to 30 percent.”
As part of the strategy, Ward/Kraft evaluated numerous potential vendors to supply the automation technology and service needed to build the machines. After working with Siemens Energy and Automation on previous PLC and software retrofits, Ward/Kraft tapped the company to help build Ward/Kraft’s first servo driven finishing machine.
“The way we select vendors is to listen to them and do our initial research with them,” Adamson said. “That is how Siemens was chosen to help build our Versatile Pressure Machine (VPM04) finishing machine. They backed up their claims. We gave them the opportunity because of the commitment they made to our program.”
LINE SHAFT PROBLEMS
The older versions of the VPM were all line shaft driven. One main 20 HP motor ran the entire machine via a line shaft,” said Adamson. “Registration throughout the machine was not consistent and mechanical breakdowns were much too common. The reinsert system, also driven by the line shaft, was a mass of belts and pulleys and also contained a correction gearbox, correction servo, encoder and other sensors and components.”
Adamson said the registration adjustments on previous VPM machines were made using hand cranks and a correction gearbox. He said the company also experienced difficulties with accuracy when making small adjustments via the correction gearbox. “During setup, the quicker the operator can register the machine the less waste is involved. Minimizing waste has always been top priority when redesigning machinery,” said Adamson.
BETTER REGISTRATION, HIGHER SPEEDS
The VPM04 is a freestanding, four axis finishing machine built at the Fort Scott facility and shipped in segments to the company’s Fredericktown, Ohio plant. According to Adamson it took about six months to build the machine. Ward/Kraft worked closely with Siemens to find the right servo solution to the line shaft problem.
“We’ve been able to achieve better registration at higher speeds,” Adamson says. “In older line shaft versions of the VPM, speed changes would cause our register to move out. But now everything is so tight that we can speed up and down without having registration problems.”
“We get in rolls of paper that are specific to the type of job we’re going to print,” said Adamson. “In our industry we are known as a ‘narrow web’ company. Most of the time our products are 24 inches or less, and the majority of them fall in the 14-16 inch wide range.”
The finishing process starts when preprinted rolls of paper are loaded onto a splicer. The paper feeds into the VPM04 machine reinsert station axis at a top speed of 500 feet per minute. Once the paper is reinserted it goes through two coating stations representing the second and third axes. A fourth axis on the finishing station perforates and cuts the paper into 11” X 8 ½” sheets. The product is then folded and stacked. If needed, the paper can be run back through another machine for additional printing.
A TOTALLY INTEGRATED AUTOMATION SOLUTION
Four SIMOVERT MASTERDRIVES ™ MC drive units communicate with one Siemens S7-315 programmable logic controller (PLC) over a high-speed PROFIBUS-DP communications system. The drives technology includes a virtual master communicating speed and position data to all drives over PROFIBUS at 12 Mbaud. The PLC and drives are housed in a cabinet adjacent to the VPM04.
The PLC provides a speed set point to the virtual master, performs parameter changes for various machine set-ups, and ensures proper sequencing on machine start-up and shutdown. The processor also performs machine function interlocking.
Each drive controls a Siemens 1FT6 servomotor, one servomotor per axis. The reinsert drive unit is 5 HP and controls a 4.7 HP servomotor. Two coating stations each have 5 HP drives as well and 4.3 HP servomotors. The final finishing drive is 15 HP and controls a 13 HP servomotor. The drives were programmed utilizing Drives ES software running under the STEP 7 SIMATIC® Manager engineering environment.
One communication cable connects the system together. With the ability for motion control with PROFBUS DP, the entire system was simplified, Adamson said. Traditionally, a cable for a field bus and a cable for a motion bus were required to perform electronic line shaft and sequence control functions.
The built in capabilities of PROFIBUS DP, include asynchronous and broadcast modes, as well as peer-to-peer communication and clock synchronized tasks. This allows the field bus and motion bus to be one in the same, resulting in hardware and engineering savings. The motion control with PROFIBUS DP was configured with STEP 7 hardware configuator and Drives ES enabling multi-drive, high-speed, peer-to-peer synchronization of position and speed set points.
STEP 7’s SIMATIC Manager provided an integrated development environment, out of which:
- Drives ES Basic-programmed, design-time drive parameterization sets could be saved to disk or copied between projects. Drives ES Basic could also be used to monitor and modify drives parameters online.
- Function blocks from the ladder logic programmed run-time drive parameterization, including technological constants. The function blocks used by Ward/Kraft (PDAT_ASYNC) were supplied with the Drives ES SIMATIC software.
- Run-time drive process data R/W, including control words and set points, was handled by function blocks called from the ladder logic. These function blocks (PCD_SEND, PCD_RECV) were also included with the Drives ES SIMATIC software.
The Drives ES SIMATIC function blocks mapped the PLC ladder logic to the drives through a simple hardware configuration address. The complete range of PLC memory addresses, including data block structures, were then available to the drive communications function blocks within the ladder logic.
“Normally, we would use SIMOLINK for drive to drive communication via fiber-optic cable and then use PROFIBUS for PLC to drive communication,” Adamson explained. “We decided to use PROFIBUS to handle all drive to drive and PLC to drive communication because of hardware cost savings and programming simplicity when utilizing the Drive ES software package.”
The HMI is provided via a Siemens TP170 touch panel mounted on a central control counsel. During the reinsert process, a color mark sensor hardwired to the drive is used to read a preprinted ballot mark on the paper. This allows the drive to take a real time sample of the paper position every repeat and compare it to an actual position on the reinsert servo.
Errors are corrected by the reinsert servo utilizing a position trim value within the drive. This maintains consistent paper position throughout the coating and finishing process and allows for excellent registration. According to Adamson, in the past operators had to rely on mechanical hand adjustments to correct registration problems. Now, because of servo technology the operator can adjust the registration with the touch of a button.
The TP170 touch panel is a Windows CE-based platform providing monitoring and control functionality at various locations around the machine. The built-in MPI (multi-point interface) PROFIBUS port on the TP170 allowed for seamless integration into the S7 network back to the PLC as well as the PC workstation. The HMI screens were developed with Siemens HMI configuration package ProTool that can be integrated into the STEP 7 environment. The TP170 supports a remote control mode that automatically receives HMI configurations via ProTool on the PC workstation and reboots itself.
COST SAVINGS BOTTOM LINE
“Some of the smaller jobs on printing presses are only several thousand feet long. If you waste 500 feet, you can waste 10 percent quick,” Adamson said. “With servo drives we can cut that in half and you can see the savings. That was my sales pitch to the owners of the company when we got into servo drives. You’ll pay for them by the waste savings over the period of depreciation.
“Over time we expect to see the waste figures go down considerably compared to line shaft driven machines,” He continued. “That makes us more competitive because these savings go right to the bottom line.”