Trends In Automation
In most other ceramic businesses, the market has demanded small quantities of a large variety of parts, and these parts may have complex shapes. These plants are much harder to automate. In the past, this difficulty has kept the price tag of automation above the point of reasonable payback.
Today, automating is easier. Fast computers, which allow machines to perform complex tasks, have become a commodity. Additionally, advances in sensor technology allow measuring parameters that were not possible a few years ago. This increased capability has heightened the demand for automated components, driving their prices down. As a result, an increasing number of companies are able to take advantage of all the benefits automation has to offer.
Kiln LoadingLoading the kiln to get the maximum quantity of product through it at one time is a common challenge for the ceramic manufacturer. For example, say a dinnerware manufacturer makes ten sizes of ware in five shapes. He wants to get the largest quantity of each type of ware through the kiln, so the ware on the kiln cars should be tightly set. Of course, the ware is glazed, so neighboring pieces cannot touch.
An engineer has made a drawing of the setting patterns to maximize each type of ware and has found that there are 20 different ways to set the car to get the most efficient loading for each part. However, only five are used. Some of the patterns are complex and take the operator too long to set, so these are not used. Other patterns are not used because the operator has difficulty setting the parts with enough accuracy to keep them from touching, and defect levels in these parts are too high. The kiln is not producing as efficiently as possible.
An automated system could benefit this dinnerware manufacturer because of its consistency. One would not think of operating a kiln without automatic control. When an automatic control loop has been properly established, it keeps the temperature of the kiln much closer to the desired setpoint than a human operator could. The same is true with other automated systems.
Figure 1 illustrates how the dinnerware manufacturer’s problem could be solved with automation. The parts travel down a belt from the glazing operation. At the end of the belt is a measuring sensor that positions the center of the part at a known location on the conveyor belt. When the part was loaded into the system, the operator told the computer its part number—this is transmitted to a gantry robot as it picks the part up off the conveyor belt. The robot looks up the part number in a database stored in its controller, and finds what pattern is needed to give the maximum loading efficiency for these parts. It looks at its count of parts that have been loaded, positions the part above the next open position, and deposits the part. When the part number changes, the robot gets the new part number, and automatically changes to position these parts in their most efficient loading pattern.
Since the memory in the robot is large, the data for all the parts produced in the factory can be stored there. The robot is accurate, so it has no problem setting even the densest load patterns without parts touching.
Storage and Retrieval SystemAnother problem common to ceramic plants is the question of how to load the kiln. Kilns need to run all the time to achieve the highest level of productivity, but staffing a plant around the clock is difficult. The traditional solution is to buy a large fleet of kiln cars. A large staff is hired, so ware can be made and cars can be loaded in one shift per day. However, this is difficult to justify if floor space is not available or the kiln furniture is expensive.
Another problem arises when there are not enough operators available in the labor market: The operators must be paid a premium to work overtime, or the kiln must idle during the off shifts. However, letting the kiln idle is not an option for users of roller hearth or pusher slab kilns.
Take an electronic ceramic manufacturer, for example. He has a press that can operate one shift per day, five days per week, and produce enough ware to feed his roller hearth kiln for seven days of around-the-clock operation. There is not enough demand for the manufacturer to increase his production to fully utilize the press, and slowing the press requires adding additional shifts of operators. Using several lanes of return conveyors to buffer the product might be one solution. However, with these multiple conveyor lanes, he is not sure how the operator will gain access between the lanes to load and unload the parts.
An automated solution for his problem is shown in Figure 2. The return conveyor is replaced with a buffer car. This car runs the full length of the kiln and handles the trays of product. The product is fed to the kiln area from the operator station on a conveyor belt. The buffer car picks up trays of product and transports them to the entrance of the kiln. A conveyor at the kiln entrance moves the trays of green product from the buffer car and into the kiln to be fired. A conveyor at the exit end of the kiln moves fired product out of the kiln, back to be picked up by the buffer car. The buffer car finally moves the trays of product to another conveyor, and they are sent back to the operator to be unloaded.
Since the press works faster than the kiln, a rack system is placed along the runway of the buffer car. These are simple steel racks, requiring almost no maintenance. When product enters the system, it is placed into the rack for storage until the kiln is ready for it. When the press is not operating, product is retrieved from the rack and delivered to the kiln. Another set of racks between the kiln exit and the unloading station holds product exiting the kiln during the off shifts. If the kiln has a slow cycle, a rack of only one layer could hold all surge needed for the off-shifts. If the kiln has a fast cycle, the buffer car can be equipped with an elevator, and the rack can be as tall as the factory ceiling. This is an easy system to maintain, since there are just a few short conveyors and the buffer car.
Factory LayoutFew ceramic manufacturers have the luxury of starting with a fresh plant when they need to make a production change. New equipment is usually placed wherever space can be made available. Figure 3 illustrates a problem faced by a new plant manager. Three kilns are installed along the factory walls, and she also runs a forming operation and a finish operation. Product flow through her factory is difficult even when moving product manually, so she has been charged with tying all of these systems together with an automated ware moving system.
A robot vehicle such as an electric monorail system (EMS) could be one solution to her problem. An EMS runs suspended from an overhead rail. The EMS can have many independent carriers operating on the rail simultaneously. Each EMS has its own drive motor for smooth starts and stops. Rail switches direct each EMS carrier in the appropriate direction at junctions between the rails.
Another, more flexible option may be to use an automatic guided vehicle (AGV) to move the product through the plant. An AGV drives on the factory floor using a laser guidance sensor mounted on a mast. It travels in the existing factory aisles, and uses targets placed on the building columns to determine its position in the factory. Bumpers on the AGV detect any obstruction in its path and stop the AGV before impact. An AGV does not need any wire connections. Directions are given to each AGV over a wireless communications link. Each AGV has a battery pack, and these batteries are recharged during idle moments in the AGV cycle.
Systems for Today—and TomorrowThe examples in this article are not just a description of what could be done—systems like these are operating today in ceramic factories around the world. They handle dinnerware, sanitaryware, ferrites, electronic ceramics, technical ceramics, structural clay products, artware and many other types of ceramics. These are the systems of today.
Tomorrow’s systems will provide even more benefits for ceramic manufacturers. For instance, increases in computing power will allow machines to see. Consider the kiln-loading example on page 31, with oval parts coming down the belt in a random orientation. A vision system will allow the robot to know how to orient the ovals, so all are in line. Vision systems using light or ultrasound will allow green products to be inspected as they travel by on a conveyor belt, and defective green parts will be rejected before they are fired.
The mechanical components of automated systems will get smaller, allowing more degrees of freedom in each movement. Finally, as more automation becomes practical, more automatic machines will be built, which will drive the price for automation down.
Systems that were easy to automate have been in place for years. As each year passes, systems that were once impractical to automate become possible. Soon, the types of systems that can be automated will be limited only by the creativity of the system designer.