Machine maintenance is best described as a balancing act. Juggling planned downtime versus production time, replacement parts inventory versus unplanned downtime and maintaining versus upgrading are just a few of the decisions you will face in the days, months and years ahead. In this article I will cover some of the basics in machine maintenance. As always it is important to contact your machinery supplier for schedules and procedures that are specific to your equipment and situation. Remember to lock out and tag it!

Controls

            Machine controls today can be very sophisticated and will provide a long service life. PLCs (Programmable Logic Controllers), input and output cards, high speed counter cards and alike have come a long way in the last few years. Usually contained in water resistant (NEMA 12) enclosures or better, these components require specific temperature and humidity environments to operate effectively.

            Most controls manufactures require that temperature ranges be maintained from 32 to 140 degrees F (0-60c). Humidity levels must be maintained from 5% to 95%, non-condensing.  In order to achieve these parameters try these simple suggestions.

            First and foremost, keep the dang door shut! Sounds simple right? But too often when visiting pallet plants the enclosure doors are left open for ease of access, exposing thousands of dollars of equipment to an uncontrolled environment. Well, since the door is open, let’s check out a couple of items. Most cabinets will use a fan and a bar type heater to maintain both temperature and humidly. Make sure they are both operational. If no heater is installed, a simple small light bulb, wired in to a switch, will provide sufficient heat in most applications.

            Inspect terminal strips and relay bases to insure that the wires are properly inserted and connections are tight. Locate all operator switches and inspect contact blocks. Pay special attention to emergency stop and rest buttons. Visually inspect the condition of the wires coming into and out of the enclosures.

            Most modern PLCs have a battery backup to keep the program information after the power is shut off. Setup a yearly schedule to replace the battery before a problem occurs. In our systems, like most others, the batteries must be replaced during a power on situation. Only allow your most qualified staff to handle this task.

            Inspect the outside of the enclosure for damage. Also note the isolation mounts, if provided, to make sure they are effective and secure.

Electrical Input Devices

            Input devices can be classified in five general categories – mechanical, retro reflective, diffuse photo, proximity sensor and opposed mode sensors.

            Mechanical devices are typically limit switches, operator controls and encoders. These items require contact to operate. Limit switches are typically activated by moving mechanical devices. Maintaining switches often requires that their mounts are positioned correctly. This will achieve the most consistent operation without overloading the mechanical head assembly. Switch heads are also set to operate in one direction or both directions, depending on application. Cables and conduit must be routed to prevent damage.

            Operator controls must be maintained to insure correct operation. Use of “gloved hand” controls help operators in most environments. A new addition is the “Touch Screen” operator interface. These units allow machinery manufactures to put more operational and diagnostic controls in the hand of your operators and maintenance staff. Yearly screen calibration and cleaning the screen is really all the attention these touch screens need. Encoders are counting devices that are driven by belts or a direct connection to a revolving object.

            Encoders are typically selected via counts per revolution. The number, say 336, is the amount of count pulses per single shaft revolution. Also pulley and belt applications are important to maintain the correct relationship of the driven shaft. The single biggest cause of encoder replacement is bearing failure, which causes count issues. If the encoder is belt driven, belt tension should only apply minimal side load to the encoder shaft. If it is a direct drive application, alignment issues will cause failures. Encoder pulleys, although very durable, do wear out or break down. Worn pulleys are usually masked by increasing belt tension to keep counts correct. That usually leads to encoder failure as stated earlier. When a pulley fails, the inner hub in the outer pulley will separate and slip. This may not be noticeable unless the pulley is removed and inspected.

            Retro reflective devices shoot a beam at a reflector and receive the signal back. The Viking Champion uses this technology to “sense” a pallet in the stacker. As a pallet enters the stacker the beam is broken, sending that signal to the PLC. Inspect the mounting bracket and the cord for the device. Also the reflector mount should be inspected. Alignment is the key to correct operation. Also make sure that the reflector is not damaged.

            Diffuse photo sensors shoot a beam at an object and receive the signal back. Viking uses this technology as a board sensor.  This unit does require care in setting internal adjustments. The range must be set to “see” the intended object without picking up other non-targeted items. Care must be taken not to cloud up the lens with oils or cleaning fluids when maintaining other nearby assemblies.

            A proximity sensor “senses” a metal object in close proximity.  The range is very limited. Close inspection for damage is the key. Clean off any grease and debris on the sensing head. Sometimes the metal shavings captured by the grease will send false signals.

            Opposed mode or through beam sensors consist of an emitter and a receiver. A beam passes from the emitter to the receiver. When the beam is broken we get an input signal. Alignment here again is the key. Through beams are usually wired so the input is on until the beam is broken. Make sure the mounts are tight and not damaged.

            One question I am often asked is how to determine which of these devices should a pallet manufacturer stock? Start by talking to your maintenance staff and make a list of items they have replaced in the last 24 months. Then sort these items into critical, necessary and just in case. Items should be deemed as critical if failure will cause complete termination of production. As a top priority, stock these items with inventory controls and a reorder procedure. This list will change as the equipment gets older. Items in the necessary pile are items that may reduce production but not prohibit it. “Band-aids” solutions can be applied to keep production going, even at reduced levels. All other items are just in case. Remember any items that put operators or staff members at risk are ALWAYS deemed critical. 

            Whether it is a Viking Turbo 505 or a thin kerf band saw, maintaining system controls and input devices is critical to machine performance. These items can be the highest cost to replace, and repair options are limited. The greatest mount of machine downtime is attributed to the diagnosing and replacement of these items. It only makes sense to protect and maintain these items.

            Jim Gookin is a technical troubleshooter for Viking Engineering. Jim can be reached at JimG@vikingeng.com.