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| Home > Articles > The Technology of Flexible Automation |
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The Technology of Flexible Automation |
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The elimination of this variation is one objective (benefits) of automating the discrete part production process.
Additional benefits include a reduction in required floor space, reduced delivery and production lead-times, higher utilisation, increased quality, and smoother implementation of changes and improvements in product design. Another significant benefit is the ability to mass-produce with a machine tool that is able to produce identical parts and with the ability to switch production between part types of different designs. This latter capability comes from the part programs stored in the local machine memory, or downloaded from a centralised storage device when needed. Effectively, this is a step towards gaining the benefits of both mass production and job shop customization, commonly known as mass customization. Mass customization refers to the practice of producing single parts or small batches to custom modifications to a part design. Flexible automation helps to achieve mass customisation. Flexible automation is created when the CNC machine tools are augmented by ancillary equipment such as automated materials handling systems, automated inspection, and central controllers. The materials handling systems are responsible for loading and unloading parts from the machines, transporting parts between machines in the system, and handling work-in-process inventory storage. These materials handling systems could consist of robust arms, conveyors, automated guided vehicles, and gravity feed chutes. Most commonly, a combination of these technologies is used with human operators introducing unused parts into the system and for removing finished parts from the system.
Another aspect of flexible automation is the usage of multiple cutting tools to perform each operation on a part and the automatic changing of cutting tools at each CNC machine tool in the system. A magazine containing cutting tools is located at each machine, and cutting tools are automatically changed (i.e. without human intervention) as the part program dictates. Typical tool magazines can hold 30-90 tools. The selection of which tools should be loaded into which magazine is known as the loading problem, which is one of several production planning problems associated with flexible automated machining system. Occasionally, centralised tool magazines permit the sharing of tools between various machine tools, potentially reducing the total tooling cost. However, this requires additional tool transportation devices and a more difficult coordination activity by the central computer system.
The central computer system is another feature of flexible automation systems. The central computer system differs from the local computer controller that resides at an individual machine in the system. It has an integrative role of managing the overall operation of the system. The responsibilities of the central computer can be divided into off-line and real-time activities. Typical off-line activities include effective planning and scheduling for the most productive use of the system during a given production period. Typical real-time activities include monitoring the operation of the system, adapting the schedule and production plans when problems arise, and alerting personnel when catastrophic failure occurs. The degree of intelligence and automatic control in the computer system varies greatly across systems, with level of human intervention. When the central computer system is also responsible for downloading the part programs to the workstations, the system is known as distributed numerical control.
Other ancillary equipment that is contained in flexible automation systems is some form of automated inspection system that checks the location of either the raw part, the specifications of the finished part, or some intermediate version of the part, or several of these. Video cameras and automated gauges can verify whether the part adheres to some pre-determined quality standard and alert the central computer when a part falls outside of the specifications.
Another form of flexible automation is seen primarily in the semiconductor industry using surface mount technologies. These machines are used to populate printed circuit boards (PCBs) with integrated circuits and other componentry. Typically the components in question are presented to the machine on large reels which are loaded onto the surface mount machine. As the PCBs pass alongside or though the machine, a component is extracted from the reel, and a gantry arm places the component into a specified location on the PCB. Sometimes the PCB itself is attached to the gantry arm and is moved to a location where the component is inserted into its correct position. The board is then moved along a conveyor to the next component loading position. The component locations are stored in computer memory, and the CNC gantry and inserter locations are controlled by this information. Different PCB designs can follow one another through the surface mount machine without disrupting the machine as long as there is sufficient commonality of components or capacity to load different component reels.
Due to the level of automation and presumed consistency, when a single part fails to meet specifications, it is a signal that some problem that could affect many parts could exist. This could be a faulty fixture, materials handling device, or worn or damaged tool. How the central computer deals with the situation depends upon the level of autonomy granted to it. Most systems will merely alert their human overseers. However, others may take action, checking various possible sources for the problem. The amount of artificial intelligence (AI) built into most industrial systems today is fairly low, largely limited to image processing and monitoring activities rather than the management of contingencies. These machine vision systems typically consist of a video camera, lighting, computer- based artificial intelligence to analyse and filter the image into a recognisable form, and a monitor to display the image and process status. The use of AI is likely to expand as the adaptive control hardware technology improves. In the future, opportunities will exist for problems to be prevented before they occur. For example, tool wear can be monitored and new tools substituted before a failed tool has the opportunity to damage a part in production. Limited applications of these are beginning to appear in practice.
Additional forms of flexible automation
While most of the discussion so far is concerned with flexible machining systems because of their prevalence, there are other forms of flexible automation. Industrial robots can be used for more than part handling. If equipped with the appropriate monitoring and sensing devices, they can perform quite sophisticated and dexterous functions such as welding, inspection, and assembly. For example, a spot-welding robot arm on an automotive production line can move more quickly across an entire vehicle, performing more consistent and rapid welds than a human operator. The flexible robot can recognise the vehicle type by some sensing technology (e.g. by identifying the fixture type) or from sequencing information from the central computer, and adapt the weld location and sequence from car model to car model. Such robots are usually trained by an operator manually moving the robot arm in a learning mode, where the x-y-z Cartesian coordinates of the robot arms position, the various arm-segment angles, and joint rotations are recorded by the robots controller for use in real production. Flexible automation can be configured in several different ways to achieve different production objectives. For example, a flexible cell is typically a single CNC machine tool possibly with automated materials handling system, and can make many part types at low volumes, sometimes one-off prototypes of products. Another form is where CNC machine tools can be lined serially with a conveyor for part movement in a transfer line arrangement to get a high throughput of a limited number of part types. A flexible manufacturing system is typically more elaborate in design, involving several CNCs doing different sets of operations, linked together logically by computer communications and physically by materials handling devices. These systems can be operated in different ways. For example, sometimes several machines may perform identical operations for reasons of system balance and/or redundancy during periods of machine failure. This then allows for different routes for parts going through the system.
The future
There is an obvious difference between flexible automation and the conventional equipment. Not so obvious is the change in management practice required to secure the benefits of the new technologies. This need was not fully appreciated initially, and early performance of flexible automation in America was lacklustre. Necessary changes extend to the planning processes needed to operate flexible automation. Stecke identified five production-planning issues necessary for effective operation of flexible manufacturing systems. Much subsequent research into FMSs has addressed one or more of these issues, which are grouping machines, selecting part types, choosing relative mixes of products, allocating system resources to part types, and determining appropriate tool magazine loading strategies. These are unique challenges faced by production managers of flexible automation that are driven by technology.
With all the advantages that existing flexible automation offer, a legitimate question is to ask, why all manufacturing is not done on such equipment. One reason is that dedicated equipment is generally faster, operation by operation, than flexible automation, and more appropriate in high-volume environments. Another reason is that there is a cost premium in the acquisition and operation of flexible automation over dedicated systems. Also, for all the tumult about the agility of flexible automation, the ability to easily modify the systems to accommodate entirely new part types is limited. Therefore, the next phase of flexible automation appears to be the development of reconfigurable manufacturing systems (RMSs), where the technology will be "designed for rapid adjustment of production capacity and functionality, in response to new circumstances, by rearrangement or change of its components." An example of a reconfigurable machine is one that has milling and drilling capabilities but currently has no capability for turning. But a "reconfigurable" machine can easily, quickly, and cheaply be reconfigured to acquire the new turning capability also. Although, RMS technology does not currently exist, newly constructed hardware and software tools offer the capability to produce newly introduced part types. Another example of RMS hardware is a milling machine with room for the addition of several spindles that can be arranged in numerous configurations. The development of the hardware, the software, and the science of reconfiguration is ongoing.
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| Posted : 10/21/2005 |
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