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Must have electronics for your web offset press

1. PLC AND TOUCHSCREEN BENEFITS INSTEAD OF MANUAL CONTROLS

The massive penetration of touchscreen based human machine interfaces (HMI) in various manufacturing processes prove a clear indication of the immense advantages of such an interface over a more traditional approach involving keyboards and mechanical buttons. To put it succinctly, touchscreen technology allows for increased flexibility, lower requirement of space, reduction in required wiring and ease of reprogramming.

One of the primary advantages of touchscreens over manual controls is the performance in tough situations. Dusts and dirt accumulate from industrial processes can enter keyboards causing them to fail; this could adversely affect the printing process. Industrial panels are employed where traditional manual controls incorporating fans or mechanical hard drives cannot hold up due to extremities in temperature, proximity to fluid sprays or high vibrations.

Touch screen panels are also employed to accommodate display of large amount of data over a smaller area as compared to hardwired pilot devices such as annunciators, gauges and chart recorders. Additionally, touch Screens provide increased interface flexibility. All printing processes with require machinery with massive complexity necessitating the use of multiple screens, contol buttons, support manuals and engineering screens. In the absence of a touchscreen interface, this would require a massive display with arrays of buttons. In such a situation the use of touchscreens serves the purpose of shrinking the system and reduces the space needed for running the machine and process.

Manufacturing costs can also be saved as the number of wired signals typically required by panel devices for termination, power and troubleshooting can be reduced. Furthermore, additional I/O points for controllers is also minimized. Typically, with HMI applications serial or other bus communications with PLCs occur. All communication using pushbuttons and meters essentially involves wiring into the I/O points onto the PLC. Consequently, this adds cost to the PLC as the analog and digital I/O points have to be dedicated as controls on the panel. Additionally, training and maintenance costs can be saved upon by customizing the graphical content with required labels and designs.

2. APFC PANEL FOR POWER FACTOR CONTROL AND SAVE ELECTRICITY

Power Factor is defined as the ratio of active power to apparent power and is amongst the most primary factors in the measure of electrical consumption. Given the immense cost associated with electricity consumption in today’s web offset press, it is of utmost importance to reduce the consumption of electricity and consequently minimize expenditure. To manage the power factor in relation to the load factor, capacitors of adequate and proper capacity need to be connected. The values of such connected capacitors will fluctuate with respect to the load and the existing power factor. A dip in the Power Factor not only attracts operational losses but can also invite a penalty from the electricity board. Power Factor can be maintained via one to two methods.

– The first methodology involves fixing a capacitor permanently at the load end or at the mains. This method works decently well for fixed loads like pumps and fans, however, it is impossible for loads which have variations in the load and power factor.

– The second method maintains the power factor via means of installation of an Automatic Factor Control Panel (APFC Panel). Such panels are particularly indispensable in web offset presses as electrical installations have to supply to a massive electrical load.

An APFC Panel is generally a microcontroller based programmable controller which is capable of switching between various capacitor banks of suitable capacity automatically in multiple stages. This is accomplished by directly reading the reactive load utilizing VAR sensing to ultimately maintain the Power Factor to 0.99 Lag. The capacitor banks can be selected depending on the load pattern, and in a number of stages such as 4/6/8. APFC panels are immensely effective at automatically managing rapidly changing scattered loads whilst retaining a high Power Factor. Other features of such panels include high efficiency, protection from power surges, in-built independent fuses, prevention of loading power factor in low load situations and minimization of harmonic current. In a typical printing press, APFC panel is must considering

Power Saving
Energy Audits
Harmonics Control

3. ANALOGUE DC DRIVE VS DIGITAL DC DRIVE IN WEB OFFSET PRESS

An increase in the production of faster and cheaper processors built using digital drives in place of the more traditional analog drives necessitates a discussion on its advantages. In the case of a traditional analog drive being configured as a torque amplifier, the first step is for the external controller to generate a ±10-Vdc command signal. The drive then monitors the winding current of the motor and makes an estimation of the mechanical torque required. The difference is then taken into account by a compensator and a corresponding command signal is generated. A pulse width modulated signal is then applied to an inverter which switches the accurate voltages to the motor.

Contrasting this with a digital drive system, much of the analog circuitry such as the summing amplifier, compensator, scaling amplifiers and PWM generators are all hidden inside a large block, while the power invertor remains comparable to an analog drive system. Since all the calculations are done via means of a software, new concepts such as compensation scheme algorithms can be programmed almost instantaneously. Evaluation also occurs at a much faster rate with a digital drive taking minutes as compared to many hours taken by a traditional analog drive.

Subsequently, amongst the main advantages of a digital drive system is the ease of addition of new features. Assuming a drive with sufficient processing power, the addition of functions only requires the cost of development. Another advantage is the ease of field upgradability. With the use of flash memory, new software and features as well as a bug fixes can be delivered with ease to the field without having to send the drive back to the factory. Customization for individual customers is also possible.

While digital systems do have a plethora of advantages, there are certain shortcomings as well; the main one being sampling delay. From the time of transmission of the command to the time that the drive control algorithm receives the value (digital), several hundred microseconds would have passed. The associated sampling delay reduces overall system bandwidth. Another key difference is that an analog compensator continuously monitors the current, whereas digital systems use pulse-by-pulse current control. As is evident, in case of the current reaching its maximum threshold, an analog circuit would immediately shut it off while a digital circuit’s response would be based on its duty cycle, thus, possibly allowing the current to exceed the maximum acceptable value. However, at the end of day, these are minor problems as compared to the massive parameter variations that a digital drive affords the designer, allowing him/her to have more options.

For a web offset user, Digital drive offers various clear cut advantages

Reliability
Since the press has to run each day, it becomes the most important parameter for any printer.

Print Quality
Digital drives acceleration and deacceleration is programmable and being 4 quadrant drive, it offers greater stability in power supplied to the motor. This clearly shows in printing as even the tiniest hunting in drive is eliminated using digital technology.

Scalability
Any printers does not have to think about future expansion as these drives are fully scalable and can be added as and when required

Diagnostic
All the drive errors and logs can be seen on the screen or downloaded on the computer. This allows supereme command over the problem occurred and its quickest resolution. Such flexibitliy is missing from analogue drive.

4. SHAFTED AND SHAFTLESS WEB OFFSET MACHINES

The printing quality of the web is defined by the drive system. These drive systems can be of two types: Shafted and Shaftless. In a Shafted Drive system, the shaft runs from the folder all the way to the length of the press. This design forces it to be responsible for driving and ensuring functioning of each printing unit along the entire length of the press. Incredibly high capacity motors are used to power this entire process. In a simplest shaftless drive system, each printng tower driven via an individual servo motor, with each motor being electrically synchronized. The overall register error is regulated by the means of a speed difference between adjacent printing rollers. Needless to say, this design difference provides certain key advantages over a more traditional shafted system.

A Shaftless driver system provides excellent control over the web tension right from the reelstand to the folder. There is much lesser vibration and minimized dot reproduction. In a shafted system, where all units are connected to a single drive shaft, any vibration originating at the folder would travel throughout the shaft of the press. Such a problem would require a group of sheets to be collected to measure a gain in dot size. With a shaftless system a single sheet is enough to gauge the quality of a printing unit.

Furthermore, a shaftlesss drirve system provides optimum access throughout the press, allows for smooth coordination of various printing units and also permits remote diagnostics. A profession can connect via the internet to ascertain and resolve any problems in the shaftlesess motors.

Finally, as compared to a shafted driver system, a shaftless drive has a much shorter makeready. As each component can be disengaged and worked on simultaneously, plate changes are faster and easier.

In conclusion, the productivity of your printing press is bound to increase through the use of a shaftless driver system. Of course there are some challenges such as a much more technical and difficult troubleshooting, and a greater financial investment in repairs, but in the long run these will fade in comparison to the efficiency that your press will be able to achieve with a shaftless driver system.