Background Information: Manufacturing technology

Many people, including key decision-makers at senior management levels, do not fully understand and appreciate the potential of many manufacturing technologies. You can use the material provided here to help people become more familiar with several manufacturing technologies and their potential benefits.  [The material in these sections is based on the Technology Application Guide series from the Industrial Technology Institute, Ann Arbor, Michigan.]

From here, you can access introductory information regarding the following technologies:

• CAD
• Inspection and Machine Vision Systems
• MRP
• NC/CNC
• PLCs
• Robots

Computer Aided Design
Computer-aided Design/Drafting (CAD) is the use of a computer to facilitate the processes of design and drafting. It involves the creation, maintenance and revision of a design database performed by a designer and aided by a computer. The design database includes both geometry and other associated information including dimensions, tolerances, part finish, process instructions, part names and more. The computer releases the designer from some of the more tedious and repetitive tasks.

CAD systems are powerful tools for designers. However, too frequently CAD is considered to be simply automated drafting.  This is a gross under-assessment of its capabilities. CAD is a tool for design.  While its greatest advantages are realised by designers its benefits pervade the entire manufacturing process. It can help the designer do her/his job faster with better quality and more consistently, thus making the entire process more productive, with better design quality, at lower overall manufacturing costs.

A CAD system is not the holy grail.  CAD is not simple to implement. To begin with, the successful implementation of CAD frequently requires fundamental organisational changes. Even after implementation, significant  development work with the system may be required before any productivity benefits will be seen and there are some kinds of design tasks for which CAD is not cost effective.

To get the most out of your CAD system, follow these guidelines:

• Maintain consistent versions of vendor software throughout your organisation, perhaps through a system administrator.
  
  
• Use standard parts or parametric design programs when faced with repetitive drawing tasks.
  
  
• Maintain a consistent file naming convention for all CAD files. This naming convention should not just be arbitrary, but should have some meaning imbedded in the name. This will allow users to easily find the files needed.
  
  
• Maintain a consistent layering scheme.  Include only necessary information in CAD files. The more information contained in the CAD drawing, the longer it will take to create.
  
  
• Ensure that geometric symbol libraries are well maintained and documented. CAD users should be required to use these libraries and should have to justify using parts not in the library. For example, if there is a library containing bolts, a user should draw all bolts using the library symbols, and the designer should have to justify using a bolt size not in the library.
  
  
• Save drawing files to the database as frequently as possible during each user session. This will reduce the work lost if the system crashes. Use paper pre-printed, with title blocks, company logos, etc.
  
  
• Do not use pen plotters to generate this information. Use photo copiers or blueprint machines to make multiple copies of drawings. Plotters should not be used for this.

Benefits of CAD include the following:

• Direct labour savings (fewer drafts-people).
• Indirect labour savings. Material savings.
• Design and production of higher quality products (fewer defects and better design).
• Faster turnaround of product (throughput).
• Higher productivity from better product designs (fewer design/ manufacturing iterations).
• More accurate proposals and estimates.
• More standardisation of both design and manufacturing.
• Higher quality drawings.
• Ability of deal with more complex products than before CAD.
• Improved reliability and less uncertainty in the production process.

The following costs should be considered when justifying a CAD system:

• Initial hardware purchase cost.
• Initial software purchase cost.
• Cost of peripherals.
• Hardware maintenance costs.
• Software maintenance costs.
• Software upgrade costs.
• Training cost.
• Shipping and installation costs.
• Cost for floor-space used and electricity and lights.
• Furniture and supplies costs.
• System management costs.

Many of the costs and benefits are difficult to quantify. One approach to solving this is to consider the opposite, that is, what are the costs of not installing CAD. It is also possible to assign probabilities to various outcomes and arrive at a cost and a benefit, given various scenarios. These scenarios can then be combined to give the value of different options. Such techniques are covered in many finance textbooks and are called expected costs techniques.

Bear in mind the following when calculating costs:

• Concepts can be taught on non-production equipment. This means that initial training can be done using a PC CAD system, even if your company has installed a much larger and more sophisticated system.
  

• Assume all equipment must be replaced within five years. The state of the art will have advanced so much in five years that you can probably save money in addition to getting a much more powerful CAD system by upgrading to a new system. Five years is the longest period to consider. Shorter periods might be appropriate.
  

• Assume that your old equipment will have no salvage value. This is based on the same assumptions as the previous statement.

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Inspection and Machine Vision Systems

Monitoring, inspection and verification systems
The increasing demand for high-quality products at comparatively low cost has led to the need to identify process and product irregularities as early as possible and to control process parameters so that the production of defective products is eliminated. Toward this end, many types of monitoring and verification systems have been developed.

Monitoring involves generating data about a process, machine, tool, or part. The objective of monitoring is to detect undesirable states early enough to avoid machine downtime and product scrap. Monitoring data could be gathered 'manually' by people or automatically by sensors. When monitoring is performed automatically (without human support), sensors generate data and feed it to a monitoring controller. Verification (or qualification) is a procedural monitoring function where the results of the procedure (assembly of parts, etc.) are checked to ensure they meet established requirements. Monitoring and verification lead to a control requirement where some action is taken as the result of the data collection and analysis.

The process of determining the most appropriate technology and then selecting specific equipment for monitoring, inspection and verification systems, requires consideration of the manufacturing operation, the environment, the object or system of interest, and the characteristics of the sensor itself. Based on these considerations, measurement specifications can be developed and used to select the most appropriate piece(s) of equipment. These specifications might include such items as measurement range, rate, accuracy, repeatability, resolution and reliability.

Typical steps involved in selecting a monitoring system are:

1. Establish the needs and requirements. Define the needs for a monitoring system and identify the functions to be performed.
   
   
2. Gather application details. Compile details on the process, work-piece, tools, machine, etc. The selection of a specific monitoring technology is influenced by a large number of application-specific constraints and requirements.
   
   
3. Identify suitable sensing parameters. Identify the sensing parameters (e.g. force, vibration, temperature, dimensions) that are appropriate for the specific application. Define the accuracy, repeatability, sensitivity, speed of measurement, reliability, and plant-floor hardening requirements.
   
   
4. Identify feasible solutions. Identify the solutions that satisfy the requirements and other constraints.
   
   
5. Select the optimum solution. Perform technical and cost/benefit analyses to select the optimum solution.

System selection
Several factors must be considered when selecting sensors for monitoring and control. The final choice is determined by a weighted combination of several critical factors such as:

• Parameters to be measured. Parameters to be measured or inferred may include some that are specific, such as dimensions, forces, and displacement, as well as fairly standard parameters such as flow, pressure, temperature, or level. Some of these parameters can be measured directly, but most must be inferred from some other measurement or combination of measurements.
  
  
• Range. Range and signal levels are primary considerations in sensor selection. The expected abnormal and normal range, linearity in this range, and sensor zero or off-set must be considered.
  
  
• Allowable uncertainty. A legitimate error analysis must be made before a sensor can be selected intelligently. Often a trade-off must be made between a desired level of uncertainty and the cost of attaining it. Environmental effects on uncertainties, which are often neglected, should be included if they are known.
  
  
• Environment outside the sensor. Several environmental variables such as temperature, vibration, and humidity may affect the operation of a sensor. These parameters must be considered carefully when selecting a sensor. Neglecting environmental effects on a sensor can cause serious problems when the sensor is used.
  
  
• Type of output. Digital output is convenient for transmitting data. The output of a sensor may be modified by signal-conditioning systems. Embedded microprocessors now provide intelligent sensing to perform these and other complex functions.
  
  
• Maturity level. A key factor in sensor selection is the determination of whether the requirement can be satisfied by a "tried and true" measurement or requires a state-of-the-art measurement.
  
  
• Reliability. Factors to be considered when evaluating reliability requirements include ease of repair, cost of downtime, and the consequences of failure. Usually the best source of reliability data are other users and literature describing the sensors as used in similar applications.
  
  
• Cost trade-offs. An estimate of the costs and benefits of the sensor is needed since cost trade-offs drive sensor selection.
  
  
• Response time. The response time can be a critical parameter. Quite often there are trade-offs among accuracy, response time, and cost.

Care in sensor selection may make the difference between success and failure for an entire project. A list of important parameters should be compiled, considered carefully, and weighting factors should be assigned. In this way, the evaluation and selection of sensors can be carried out systematically.

Vendor Selection
Once a suitable sensor technology is selected, identification of appropriate vendors and selection of the one who best satisfies the requirements must be made. Selection involves:

• Developing a tender document. The requirements for the sensor system must be clearly defined in the tender document so that the vendors can provide the information needed for evaluation. The specifications should include the functional, performance, and other auxiliary and control system requirements.
  
  
• Evaluating the proposals and selecting a vendor. Evaluation criteria must be developed to compare the proposals received from vendors. The criteria may cover issues such as cost, performance verification, fit with requirements, and the reputation and experience of the vendor. Cost should not be the only criterion in evaluating the proposals.
  
  
• Work with the vendor. Detailed specifications, installation, and training requirements should be developed by closely working with the selected vendor. The responsibilities of the vendor and the acceptance criterion must be clearly defined before an order is placed.

Any sensor system should have a written document listing:

• The limitations of the system. This covers what the system can and cannot do.
  
  
• Operating parameters. This is a listing of the conditions needed for the system to work properly. The list might include temperature range allowed or humidity required for proper operation.
  
  
• Job descriptions and training requirements. These are needed for people associated with the system.
  
  
• Information analysis. What to do with the information gathered by the system.

In addition, you should have a detailed schematic of the system. This will be useful for any repairs or modifications needed. Any programs used in the system should include a listing. Troubleshooting and repair instructions should be included.

Implementation issues
Because implementation is the last of a long string of events in the development, choice and use of a sensing system, planning for implementation usually takes place rather late in the process. Unfortunately, this is a highly dysfunctional approach. Implementation must be considered from the beginning. Even during the selection process, the sensor system must be chosen with consideration for how it will be implemented. It may be that the system you optimally want is too difficult or time-consuming to implement, or its use may not fit within the existing organisational culture without major change happening first.

Be sure to consider the following types of issues:

• Organisation design. The design of an organisation consists of such elements as mission, its structural hierarchy, the division of labour, coordinating mechanisms, and the reward system. These factors can all have a serious impact on a sensing system's implementation. For example, if an organisation's reward system tends to reward only gross levels of production, there may be no incentive to produce "quality" products, and consequently no incentive to monitor and use sensor data.
  
  
• Job design. Unless job designs are changed to work with the new sensor system, it is likely that the sensor will not be used effectively. Consider a first line supervisor whose job before the installation of the sensor system was to oversee production personnel and make sure they did their assembly jobs. To make effective use of a new sensor it may be necessary for production employees to check the sensor output regularly and for the supervisor to work closely with them to make decisions about when to make changes in the manufacturing process based on the data. Both the production employee and supervisor jobs have been changed. For example, they will need new problem-solving and team-work skills, and more time to assess data and solve problems. Unless the design of the work system is changed there will be problems.
  
  
• Involvement of relevant parties. Even the most knowledgeable engineer does not know everything regarding a particular sensor installation. S/he may lack important information about such things as customer needs, the quality of raw materials, and the day-to-day operation of the factory. The only way to get this information is to involve the relevant, affected people. A good way to do this is to form a project team with representatives of all relevant groups: operators, maintenance, marketing, purchasing, etc. The team will not only provide needed information, but give a preview of how the affected parties are likely to react when confronted with the new technology. In addition, members of the project team are more likely to buy into the project and help sell it to their peers throughout the plant.
  
  
• Training. Although it may be obvious to some that operators, maintenance staff, and engineers will need to be trained to use the new sensor system, many companies provide too little training, too late, and of the wrong kind. Training must be matched to the type of technology and the type of trainee. Most people need a combination of class-room work and structured practical experience. Frequently, production employees receive a few hours of class-room work and are told to "go play with the equipment" to get their on-the-job experience. This is not adequate. It is also essential that training be provided early in the process. It is not unusual that the immediate need to get the technology "up and running" makes people neglect involvement and training. This leads inevitably to problems. For example, employees who are being trained cannot be expected to be highly productive. If a quick start is required, then training must be provided before the equipment arrives.

Cost and Quality Benefits
A monitoring system could provide the following productivity, cost and quality benefits.

• Reduced downtime. Catastrophic failures and crashes are detected immediately and the equipment controlled before serious damage can occur. This reduces machine repair downtime and increases machine productivity.
  
  
• Reduced scrap and rework. Since detection and reaction to process variations are prompt, fewer defective parts are produced. This reduces the scrap rate and rework time needed to correct defective parts.
  
  
• Less cost. Elimination of serious damage to equipment reduces the tooling and machine replacement costs. This also minimises the costs associated with repair and maintenance.
  
  

Machine Vision
A machine vision system is a specific type of monitoring, inspection and verification system. It may be thought of as being something like the human visual system in that it is made up of a camera (eyeball) and a computer (brain), and it will try to interpret a scene in much the same way that a human does. Although it does not have the judgmental capabilities of a human, it does perform better than humans on repetitive tasks requiring long spans of attention.

In one well-known study, human inspectors were asked to distinguish black and white balls passing by on a conveyor. Although the balls were easy to see and speed was not a problem, their success rate for this simple task was less than 80 percent. This dramatically points out the lack of tolerance of humans to repetitive tasks. Machine vision systems, however, handle these types of tasks with accuracy and ease.

Machine vision has a another major advantage; it is quantitative. A machine vision system is able to produce numerical values for the brightness of different parts of a scene and it can distinguish and measure exact distances. On the negative side, a machine vision system is generally not able to make complex judgements.

Generally, a machine vision system consists of one or more cameras used to obtain electronic images of the part(s) to be measured or inspected and a computer, or "vision engine," to condition these images and perform any analysis required to complete the inspection. The entire visual inspection system, however, consists of much more than the vision hardware. For example, the mechanical assemblies required to present the product correctly and reliably to the camera for inspection, the lighting configuration, and the type of optics that will best present the image to the camera all must be considered part of a visual inspection system as well. A final consideration is what will be done with the information collected? All of these elements are interrelated, and by ignoring this "integrated systems" aspect of visual inspection, you can incur great expense or failure.

Some implementation issues
A critical success factor with machine vision systems implementation is involvement of the end user. If it is used for final inspection, inspectors should be very familiar with the system. If it is used to help run a machine, the machine operator should know it well, or else it will not be employed fully. Although the human-machine interface for many vision systems is designed to be "user friendly" (functions are accessible through menus, and all the right "bells and whistles" are present), if they are to used effectively they require that the user have a good understanding of what the system is doing and how it is doing it.

Training for users is frequently provided by the vendor as part of the cost of the system. Generally speaking, people such as machine operators, inspectors, maintenance people, and representatives of plant engineering should participate in the training.

Normally, upkeep of the system will not require more than the usual maintenance staff. Frequently electronic troubleshooting will be explained in detail in the instruction manuals for the system and repairs are relatively straight forward (e.g., the replacement of defective components such as light bulbs or complete printed circuit boards). Of particular note is that fact that maintaining the system should not require the hiring of optical or electronics technicians.

Unless the specific application is particularly simple and the in-house engineering staff has experience in the use of machine vision, you should not implement the system without help from the vendor or a systems house. Engineering and production people should be involved in defining what the vision system is to do and how it should be done. They should contribute enough knowledge of the manufacturing process and its problems that the vision vendor will not try to solve the wrong problem.

In all cases, the basis for acceptance of the system should be defined quantitatively at the outset. This will avoid the unfortunate scenario of finger-pointing when the system performance does not measure up to ill-defined expectations.

The in-house engineering staff may also want to take on the responsibility for providing the mechanical handling necessary to present parts to the vision system and to remove defective parts from the production flow, although this requires careful coordination with the vision vendor. It is also vital that the end user knows what to do with the information generated by the system and how it integrates into the overall company quality program.

Choosing the Vendor
Once you have a fairly good idea of your requirements, you should start to talk to vendors. It is important to compare your needs to vision system capabilities and costs very early, since definition of the problem with no concern cost can be a mistake. Often, you and the vendor can arrive at compromises that will lower the cost and raise the probability of success of the vision system. Vendors can also define the constraints placed upon mechanical handling, environment, and people-related issues at an early stage of the implementation.

Documentation received with the system should include an explanation of the operation, normal maintenance requirements, troubleshooting instructions, and mechanical and electrical drawings. If the vendor supplies controls with the system, control drawings should be included. In addition, the vendor should have a field service organisation that is responsive, since the vision system can shut down your production if it fails.

Cost and Quality Benefits
The impact of manufacturing-generated defects can range from rework and/or scrap, to damage of downstream tooling, and to faulty end products. In addition, the sale of defective products to customers could incur warranty and/or liability costs along with a likely loss of market share and customer goodwill. Thus, choices of location for defect detection capability, choices of product characteristics to be checked, and choices of methods to detect defects, collectively pose a possibly complex but important challenge to manufacturing and product engineers.

While some methods of defect detection, like manual contact gauging or visual detection of flaws by "expert inspectors," are relatively inexpensive (though not necessarily entirely effective), other methods such as machine vision can call for substantial capital investment. On the positive side, however, operating benefits such as higher effective capacity for the same investment, lower operating costs, and improved customer response to product can accrue as a result of this investment.

Although there is no simple formula to describe the costs and benefits for all potential machine vision applications, it is important to go through the exercise of considering them as early as possible. Remember it is misleading to consider only the effects on inspection labour itself and to ignore other ramifications of quality improvement that can be obtained from the investment.

Manufacturing Resource Planning (MRP)
Manufacturing resource planning (MRP) is a computer-assisted methodology for planning and controlling a manufacturing company. It is more than a computer system. The computer and software are tools used by people to efficiently execute the methodology. MRP should be considered primarily a 'people' system. The task of MRP is to help you plan the manufacture of the correct product, at the right time, taking into account financial and capacity restraints, and providing information to facilitate the control of the plant to execute the plans.

Many manufacturing organisations think that they can not use an MRP system. People think that MRP can not help them if their products are unique for each customer order, if they do not have assembled products (like a complex machined aerospace part with no assembly) or if they do not need to manage a finished product inventory. Other organisations rushed into MRP believing it would solve all their operational problems. They were, of course, disappointed. Still other organisations considered their operation so unique that it required custom software. Frequently, re-specifications and huge cost overruns plagued these custom developments. MRP can be used effectively regardless of the product manufactured. Studies show that 94 percent of manufacturing activity has to do with information (including decision processes) while only six percent is hands-on labour (machine operation). MRP is a computerised manufacturing planning and control system and, therefore, can be a valuable tool for almost any manufacturer. It takes the right attitude and a lot of preparation, however, to make it work.

MRP is an integrated system. The advantage is that, for example, it can join sales order processing with accounts receivable and the master production schedule. Data is only entered at one point in the system. Success with MRP comes by recognising how to use the "tool" in your specific environment, knowing your requirements for the system and selecting an implementation path that will give the greatest benefit in the shortest time.

Who Should Consider MRP?
It is easier to say who should not consider MRP at first. MRP would be "overkill" for a small (up to 20-person) jobbing tool maker or machine shop handling jobs that repeat infrequently and have little commonality in product structure. These shops would benefit most by installing sales order processing, financial controls and tools to help them with estimating, job costing and possibly finite scheduling.  For other organisations, learning how to apply the system is the most important first step. This is achieved only via a thorough education and training program involving the entire organisation, including top management. This educational process can take up to 18 months before the commitment to invest in an MRP project is made (some organisations have taken four years before they purchased their system).

Organisations that have successfully implemented a system list the following benefits: tighter operational control of the company, increased inventory turns, on-time shipments and a much improved quality of work life.  However, the risk for the small company is high. The investment is large and it has to work. The cost of failure will result in a severe drain on resources restricting further strategic investments. The selection has to be right the first time, and for the first-time user, the lower the cost to meet the minimum requirements, the better.

Implementation issues
The best advice to give is to stay calm, do not rush and prepare well. Use the processes and tools provided on this CD-ROM.  If you have not worked with MRP before, get expert help and advice, outline your requirements (preferably with an experienced consultant assisting this process), set up your support infrastructure (define the operating procedures), consider you critical success factors, create a realistic implementation plan, cost justify the project, and thoroughly educate and train your work force from owners to operators. You will gain much even before you cut the purchase order!

The project team's mission is to define the information a company currently uses, who uses it and why. From this, the project team defines the improvements they want from a manufacturing resource planning system and what changes must be made to the way the organisation currently operates to make the system work. The product of the project team's work is a detailed implementation plan and a specification of system requirements.  Note that MRP can be customised only so far. Although every company has a unique "personality" or culture, it is unrealistic for you to expect the vendor to completely customise an MRP system for you.  If you expect this to happen it is a good indication that the project team has misunderstood manufacturing resource planning.

Vendor credibility is critical to implementation success.  There are several issues to consider:

Documentation. User manuals that come with the software package are critical to a successful system adoption. The standard of the user manuals should be a major selection criteria. It should help the selection team decide if the package's capability can meet the functional specification defined in the implementation planning stage.

Telephone Support. The system must be supported by the vendor at least eight hours a day, five days a week. Additionally, the vendor must be able to respond to a tough question in at least four hours. Visit existing installations and solicit vendor recommendations. It's a good way to assess vendor capability.

Vendor Training. The vendor must offer frequent training sessions (at least monthly) for system administration and for each module within the package. The amount of training supplied free with the software package is never sufficient to guarantee a successful implementation. In fact, the current trend is for the training to be provided at additional cost.

Maturity of Product. This technology is constantly changing as new programming environments are developed. Thus, high functionality at low cost is a trade-off with the maturity of the product. Sufficient packages are available. A company does not need to engage in custom development (even Fortune 1000 organisations buy packaged MRP software) or become a beta test site. It is necessary to establish that the vendor has at least three or four successful installations.

Location. The location of the hardware vendor is critical. The systems support engineer must be local to guarantee responsive service. For software, vendor location is less critical. Sometimes, a vendor's support centre can access a client's system remotely via modem for any problems that can not be resolved by telephone.

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Numerical Control/Computer Numerical Control
Machine tools such as lathes, mills and drills form the basis of machine shop technology producing metal products. Historically, such tools we controlled manually. In the 1950's, however, a new method of controlling machine tools, now known as numerical control (NC) was developed. Automation of machine tools began to see wide-scale implementation in the 1970's with the advent of what are now referred to as computer numerically controlled (CNC) machines.

Definitions/Explanations
Computer-aided machining (CAM) is a computer-based process that helps define and create the program to drive CNC machines. CAM/CNC can be thought of as the use of a computer to control the machining sequence of a machine tool, a technology offering three significant benefits over manual machine tools: (1) faster production; (2) more accurate and consistent work, resulting in higher quality; and (3) extended capability - the ability to make parts that are impossible to make by hand. CAM/CNC can be thought of as consisting of two broad areas: computer-controlled machines (NC, CNC and DNC machine tools) and the computer-aided tools for programming these machines.

The CAM/CNC system is extremely flexible, capable of being linked directly to computer-aided design (CAD) systems to provide even greater quality, flexibility and overall productivity gains. This integration of computer technologies in CAD and CAM offers manufacturing one of the greatest opportunities for improving productivity and performance.

• NC (Numerical Control) refers to controlling machines directly using punched tape; the controller has no intelligence and can not be modified in any way without changing the wiring of the machine.

• CNC (Computer Numerical Control) refers to controlling machines using microcomputers at the machine, although the method of reading the program into the controller may still be by punched tape.

• DNC (direct numerical control or distributed numerical control) refers to controlling machines or machine cells (a group of related machines) using a centralised computer. DNC systems originally had machines without individual controllers that were all controlled from a central computer (direct numerical control); currently, DNC is typically used to describe a system in which each machine has its own controller and is, in turn, linked to a central computer system that coordinates the machines and trains a list of part programs that can be down-loaded to a machine as needed; this is more accurately known as Distributed Numerical Control.

The CAD/CAM Process
CAD/CAM development is comprised of three major steps:

1. Geometric model creation - defining the geometry of the part.
   
   
2. Part program creation - defining tool paths and other machine control information.
   
   
3. Post-processing - generating a machine-specific program to produce a part.

Choosing a machine and vendor
CNC machines are large and complex pieces of equipment. They do break down from time to time and will need repair. In some shops, the machines will be integrated with other machines. This interdependency makes reliability, maintenance and repair, major concerns. These factors suggest several criteria on which to base vendor selection:

• How fast can the vendor fix it if it breaks? Does the vendor have spare parts and service personnel on hand that can get to your shop quickly? Can the vendor help fix minor problems with simple phone guidance?
  
  
• What is the availability of training? Does the vendor have a good training program, is it run often so new employees can attend, and how much does it cost? Is alternative training available at local sources?
  
  
• What types of controls are available? It is much simpler if a shop has only one or two different types of controllers to deal with. Many different machine tools use the same controllers.
  
  
• How willing is the vendor to share details of the electronics with you? If you intend to integrate these machines, you will need to know considerable details of the controls and the wiring. Many vendors are not willing to help a user in this area.

Cost and quality benefits
Four basic benefits accrue to the CNC machine tool user versus one with a manual or hard-automation type of machine.

• Greater accuracy and repeatability. A part can be made over and over again exactly the same within the limits of the machine tool. A variety of on-machine sensors help ensure that the parts re within tolerance and that there are no other problems with the machine that would affect quality.
  
  
• Increased capability. CNC enables the user to make parts that can not be made any other way.
  
  
• Faster set-up compared to manual or hard-automated machines.
  
  
• Capability of running in a lightly attended mode. This means that production is not tied to having an operator at the machine. The operator has only to check on the machine occasionally and solve minor problems that might otherwise stop production.

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Programmable Logic Controllers (PLCs)
A programmable logic controller (PLC) is an industrial computer with built-in connections for electrical equipment. It is generally programmed by an external device in ladder logic. Ladder logic programming allows maintenance personnel to examine and modify the detail of the control logic. This access is valuable when troubleshooting the system.

An industrialised microcomputer is a rugged version of an office personal computer (PC). The microcomputer requires external devices to connect to electrical equipment and it runs both purchased or custom software, written typically in Basic or 'C' language. Operator interface is the microcomputer's strength. When the operator is entering or seeing a lot of information, the microcomputer is an appropriate tool.

Programmable controllers were originally built to replace relay logic in machine control. Ladder logic programming was developed to define the control logic in a way that was familiar to electricians who had used relay logic. Some of the jargon of mechanical relay lingers in programmable controllers - contact, coil, master relay and other terms.

Think of programmable logic controllers (PLCs) and industrial microcomputers in terms of basic neurology: PLCs and microcomputers make up the brain for most new manufacturing equipment. They execute the logic required to move a machine through its sequenced process steps. But, like the brain, the controller must have a means of gathering information in order to do its work. It receives this information from sensors and actuators, the eyes and hands of the system.

Consider a simple machine that applies sealant to a part. The part is carried by a conveyor to a workstation. When the part arrives at the workstation, a fixture locks it in place. Once locked, the sealant is applied. The part is then released back to the conveyer. The sensors are often limit switches or proximity switches. These sensors connect to the controller. Sensors allow the controller to determine the physical state of the machine. The control designer, then, needs information about where the sensors will be on the machine. For example, the part arrival sensor must be located close enough to the work-spot to ensure that the fixture can lock the part into place. The part arrival sensor must be far enough up-line to disregard a part that has been locked.

Actuators are connected indirectly to the controller and are pneumatically, hydraulically, or electrically powered. For pneumatic and hydraulic actuators, the PLC output controls a solenoid valve which then controls the actuator. For electrical actuators, the low-power output of the controller (about two amps) is used to drive a contractor which switches the higher power required by the actuator.

There is a great deal of linkage between the physical machine and the controller. The physical machine, sensors, actuators, controller, and control logic all work together as a system. The controller is only a part of the overall system. Initially, your effort should concentrate on how the system should function rather than what components you will use to build the system. When the desired outcome is well understood, this document can help you select the components of the system.

Implementation issues
The system end user must decide whether to perform the controls function in house or contract it from a vendor. Assign this responsibility in a manner that best meets the needs of your business.

If you are planning to incorporate controls into your product, you should plan to bring both design and maintenance capability into your organisation. The design function will be needed for initial product design, product changes and customer support. The maintenance capability is needed primarily for customer support.

For systems that use controls, you will need access to maintenance capability. If downtime has a large impact on your business, you will want that maintenance capability in house. If you can live with one-day downtime, you should consider contracting for the maintenance support. These systems fail so infrequently, however, that technicians can not stay current on the maintenance techniques. This problem is compounded by the fact that the controller is rarely the faulty component. The maintenance technician must use the controller as a tool to determine what is wrong with the process. Contracted services generally know the controller well, but they will not understand your process.

What if the machine builder has total responsibility? In this case, the builder knows both your process and the controller. This arrangement can still mean relatively long repair times. This method seems to work best when the machine builder has a financial stake in the proper operation of the machine.  It is then in his/her best interest to keep the machine building good parts.

Cost and quality benefits
The initial cost of programmable controllers and industrial microcomputers is generally comparable with dedicated relay logic. The cost advantage is enhanced capability, ease in modifying the program and reliability. New controllers offer increased capability and value over hard-wired logic. An operator can get a written description of a problem rather than just a fault light. Changes in controllers do not require additional panel space and rewiring when requirements change. As standard components, programmable controllers and industrial microcomputers are extremely reliable, much more so than the relays that they were designed to replace. When the controllers fail, replacements are distributor stock items. This makes for a quick and easy repair.

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Robots
Robots can be a cost-effective means of accomplishing repetitive, physically demanding, or dangerous tasks. However, as with any other piece of industrial equipment, cost-effectiveness depends, at least in part, on the specific application and the type of the robot. With the introduction of non-servo-controlled robots and modular robot building blocks, opportunities for cost-effective applications have increased.

What is a robot?
First of all, there is a need to define exactly what a robot is to differentiate them from other members of the large family of automated industrial equipment. Using the Robotic Industries Association (RIA) as authority, a robot is a programmable, multifunction manipulator designed to move material, parts, tools, or specialised devices through variable programmed motions for the performance of a variety of tasks.

The programmable feature of robots distinguishes them from "hard" automation, such as cam, linkage and relay-based systems, where the control logic is fixed. The multifunction feature distinguishes robots from other forms of programmable automation such as Computer Numerical Control (CNC) machining centres. For our purposes, robots are defined as having three or more axes, enabling programmable motion for a variety of tasks within a three-dimensional work envelope. This last feature distinguishes them from programmable rotary tables (single-axis) and X-Y tables (two axes). Because there is cost associated with each of these features, determining whether the features are required is the first step in assessing a potential robot application. For example, if a potential robot application needs only one program to complete all the intended tasks, "hard" automation might very well be most cost-effective.

Cost and quality benefits:

• For appropriate applications, robots can produce significant cost and quality benefits.
• Reductions in scrap and rework when applied to tedious or physically demanding operations.
• Reductions in work-in-process when used to link manufacturing cell elements.
• Increase in cost-effectiveness when used to balance a line or to run on an unattended shift.
• Reductions in economic order quantity (EOQ) when used to reduce setup times.
• Reductions in product changeover investment over time when used instead of dedicated automation on products with frequent design changes.

While the benefits of robot applications have been significant in many cases, they are not the solutions to every problem. Frequently, improved methods within existing manual operations or "hard" automation will prove more effective.

Assessments of potential robot applications may identify more effective solutions. For example, there have been cases where the redesign of a product (in anticipation of robotic assembly) so dramatically improved the productivity of the existing manual process that robotic assembly was no longer justified. The redesign of a product to facilitate robotic assembly may also set the stage for a "hard" automation solution that proves to be more cost-effective than the robots originally intended. Also, the work-piece delivery and positioning system planned for the robot may, by itself, produce nearly all the benefits anticipated from the total robot installation; for example, the workpiece fixturing designed for an intended robotic seam welding application may decrease the cycle time on the present manual weld system to the point where robots no longer offer a significant advantage.

Finally, as noted, there are instances where other methods should be considered. For example, if a part can be slid off a conveyor, a simple single-axis, automated mechanical assembly should be considered as an alternative to a material-handling robot. If a lightweight tool with fixed orientation is to be moved relative to a workpiece, and the required tool path is in a single plane, then a programmable X-Y table may be significantly more cost-effective than a robot.

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