OCOC限制理论精髓限制理论精髓PPTPPT课课件件IntroductionIn recent years a rather unique and interesting In recent years a rather unique and interesting approach to visualizing and managing an approach to visualizing and managing an operation has emerged. operation has emerged. Originally developed by Eliyahu M. Goldratt in Originally developed by Eliyahu M. Goldratt in his book his book The Goal, The Goal, this this Theory of Constraints Theory of Constraints has allowed many people to successfully rethink has allowed many people to successfully rethink their approaches to improving and managing their approaches to improving and managing their production processes.their production processes.2 2Do. Dr. Blent SezenDo. Dr. Blent SezenIntroductionOpinions about the Theory of Constraints differ. Opinions about the Theory of Constraints differ. Some think that the Theory of Constraints (TOC) is a Some think that the Theory of Constraints (TOC) is a good way to improve process capability while using other good way to improve process capability while using other control systems such as JlT or MRP, while others believe control systems such as JlT or MRP, while others believe that TOC is a stand-alone approach completely unique that TOC is a stand-alone approach completely unique and separate from other techniques. and separate from other techniques. In this context, it is suggested that TOC can provide In this context, it is suggested that TOC can provide approaches to design, manage, schedule, and improve approaches to design, manage, schedule, and improve virtually any production system. virtually any production system. 3 3Do. Dr. Blent SezenDo. Dr. Blent SezenIntroductionStill others believe it can be either just a process Still others believe it can be either just a process improvement approach or a complete system improvement approach or a complete system approach, depending on the extent of the approach, depending on the extent of the implementation taken. implementation taken. It may not, in the opinion of this third group, be It may not, in the opinion of this third group, be the most appropriate approach for certain the most appropriate approach for certain business environments, while it may prove business environments, while it may prove highly effective for other business environments.highly effective for other business environments.4 4Do. Dr. Blent SezenDo. Dr. Blent SezenFundamental Principlesof the Theory Of ConstraintsThe fundamental concept behind the TOC is that The fundamental concept behind the TOC is that every operation producing a product or service every operation producing a product or service is primarily a series of linked processes. is primarily a series of linked processes. Each process has a specific capacity to produce Each process has a specific capacity to produce the given defined output for the operation, and the given defined output for the operation, and that in virtually every case there is one process that in virtually every case there is one process that limits or constrains the throughput from the that limits or constrains the throughput from the entire operation. entire operation. 5 5Do. Dr. Blent SezenDo. Dr. Blent SezenThe Linked Process Pipe Analogy6 6Do. Dr. Blent SezenDo. Dr. Blent SezenFundamental Principlesof the Theory Of ConstraintsThe analogy often used is that production The analogy often used is that production flowing through operational processes is like flowing through operational processes is like liquid flowing through a pipeline. liquid flowing through a pipeline. Each process has a certain defined capacity, Each process has a certain defined capacity, illustrated in the analogy by the diameter of the illustrated in the analogy by the diameter of the associated pipe. associated pipe. In the diagram shown, process E has the In the diagram shown, process E has the largest capacity to process production, while largest capacity to process production, while operation C has the least amount of capacity. operation C has the least amount of capacity. 7 7Do. Dr. Blent SezenDo. Dr. Blent SezenFundamental Principlesof the Theory Of ConstraintsSince operation C is the constraint on the entire process, it will limit the amount of output from the process, regardless of the capacity of the remaining processes. Improving any of the other operations (increasing the size of the pipe in that section) will not improve the total amount of liquid coming out of the system of pipes.8 8Do. Dr. Blent SezenDo. Dr. Blent SezenFundamental Principlesof the Theory Of ConstraintsA constraint, in its most general form, is anything that limits the firm from meeting its goal. For most firms, that goal is to make money, which manifests itself by increasing throughput-as measured by sales, not just production.9 9Do. Dr. Blent SezenDo. Dr. Blent SezenFundamental Principlesof the Theory Of ConstraintsAs a numerical example, consider the As a numerical example, consider the operation producing product A in Figure. operation producing product A in Figure. 1010Do. Dr. Blent SezenDo. Dr. Blent SezenFundamental Principlesof the Theory Of ConstraintsIt should be clear from this simple example that It should be clear from this simple example that the total operation is constrained by process 3 at the total operation is constrained by process 3 at 4 per hour. 4 per hour. No matter how much efficiency you have in the No matter how much efficiency you have in the other processes and how many process other processes and how many process improvements are made in processes 1,2, and improvements are made in processes 1,2, and 4, you will never be able to exceed the overall 4, you will never be able to exceed the overall operational output of 4 per hour unless you operational output of 4 per hour unless you address the constraints of process 3.address the constraints of process 3.1111Do. Dr. Blent SezenDo. Dr. Blent SezenFundamental Principlesof the Theory Of ConstraintsIncreased efficiency and utilization in processes 1 and 2 Increased efficiency and utilization in processes 1 and 2 will, in fact, only increase inventory-not sales. will, in fact, only increase inventory-not sales. That issue is one of the key points of TOC-the major That issue is one of the key points of TOC-the major measure for any operation should be on the throughput measure for any operation should be on the throughput of the organization, or, in other words, the contribution to of the organization, or, in other words, the contribution to sales. sales. Any other measures of process efficiency, utilization, or Any other measures of process efficiency, utilization, or other commonly used operational measures have little other commonly used operational measures have little relevance to the overall effectiveness of the entire relevance to the overall effectiveness of the entire system.system.1212Do. Dr. Blent SezenDo. Dr. Blent SezenFundamental Principlesof the Theory Of ConstraintsThis approach has implications far beyond how the This approach has implications far beyond how the process is viewed. Even accounting systems are process is viewed. Even accounting systems are impacted. impacted. For example, many accounting systems allocate For example, many accounting systems allocate overhead costs to products based on direct labor hours of overhead costs to products based on direct labor hours of production. production. Such systems may give the impression that producing Such systems may give the impression that producing more product will help to pay for the overhead costs. more product will help to pay for the overhead costs. Unfortunately, if the extra product produced is not linked Unfortunately, if the extra product produced is not linked to actual sales, the result is only more costly inventory to actual sales, the result is only more costly inventory and an overall negative impact on the business.and an overall negative impact on the business.1313Do. Dr. Blent SezenDo. Dr. Blent SezenFundamental Principlesof the Theory Of ConstraintsTOC principles make the point that only sales should be TOC principles make the point that only sales should be counted as operational throughput. counted as operational throughput. Another accounting implication is the labor cost itself. Another accounting implication is the labor cost itself. Most traditional accounting systems view direct Iabor as Most traditional accounting systems view direct Iabor as a variable cost. a variable cost. TOC principles, on the other hand, contend that in the TOC principles, on the other hand, contend that in the short run all operational costs except direct material are short run all operational costs except direct material are largely fixed and should, therefore, be lumped together largely fixed and should, therefore, be lumped together into an overall operational expense. into an overall operational expense. 1414Do. Dr. Blent SezenDo. Dr. Blent SezenFundamental Principlesof the Theory Of ConstraintsOne of the key points made by this example is One of the key points made by this example is that that products do not really have a profit-products do not really have a profit-companies do. companies do. This point helps to view the operation more as a This point helps to view the operation more as a system rather than as a set of largely system rather than as a set of largely independent functions. independent functions. Such a view is a critical part of managing by Such a view is a critical part of managing by TOC principles.TOC principles.1515Do. Dr. Blent SezenDo. Dr. Blent SezenUnderstanding and ManagingThe ConstraintsThere are several fundamental guidelines developed for understanding the TOC principles and how to manage a constraining process. Some of the more noteworthy guidelines include the following: 1616Do. Dr. Blent SezenDo. Dr. Blent SezenUnderstanding and ManagingThe ConstraintsA system optimal performance is NOT the sum of local optima. Any system that is performing as well as possible usually implies that not more than one part of the system is performing at an optimal level. 1717Do. Dr. Blent SezenDo. Dr. Blent SezenA system optimal performance is NOT the sum of local optima. I If all parts of the system are performing f all parts of the system are performing optimally, the system as a whole will probably optimally, the system as a whole will probably not be performing optimally. not be performing optimally. In other word s, it is virtually impossible to obtain In other word s, it is virtually impossible to obtain a perfect system balance. a perfect system balance. Even if the system was designed to be perfectly Even if the system was designed to be perfectly balanced, normal variations in performance will balanced, normal variations in performance will inevitably cause some degree of imbalance.inevitably cause some degree of imbalance.1818Do. Dr. Blent SezenDo. Dr. Blent SezenUnderstanding and ManagingThe ConstraintsSystems are like chains. Each system will have a weakest link (a constraint) that will limit the performance of the whole system.1919Do. Dr. Blent SezenDo. Dr. Blent SezenUnderstanding and ManagingThe ConstraintsKnowing what to change requires a complete Knowing what to change requires a complete understanding of the system and the system understanding of the system and the system goal.goal. Often in TOC, the system goal is to make money Often in TOC, the system goal is to make money through sales, not production. through sales, not production. Production completed without a sale (making and Production completed without a sale (making and storing inventory) does not contribute to the goal storing inventory) does not contribute to the goal of the company until it does become a sale. of the company until it does become a sale. 2020Do. Dr. Blent SezenDo. Dr. Blent SezenUnderstanding and ManagingThe ConstraintsMost undesirable system effects are caused by a few Most undesirable system effects are caused by a few core problems.core problems. Solving a symptom of a problem will often do little good. Solving a symptom of a problem will often do little good. If the core problem remains, the symptom (or another one If the core problem remains, the symptom (or another one associated with it) will likely reappear very soon. associated with it) will likely reappear very soon. True long-term relief from the undesirable effect will occur True long-term relief from the undesirable effect will occur only if the core problem is identified and corrected. only if the core problem is identified and corrected. 2121Do. Dr. Blent SezenDo. Dr. Blent SezenUnderstanding and ManagingThe ConstraintsCore problems are almost never obvious. They tend to show themselves as a series of undesirable effects, most of which are really symptoms of the underlying problems.2222Do. Dr. Blent SezenDo. Dr. Blent SezenUnderstanding and ManagingThe ConstraintsEliminating the undesirable effects provides a Eliminating the undesirable effects provides a false sense of securityfalse sense of security. . Working on problems (often really symptoms) Working on problems (often really symptoms) without finding the root cause tends to provide without finding the root cause tends to provide short-lived improvements. short-lived improvements. On the other hand, eliminating a core problem On the other hand, eliminating a core problem generally eliminates all of the undesirable effects generally eliminates all of the undesirable effects associated with it. associated with it. 2323Do. Dr. Blent SezenDo. Dr. Blent SezenUnderstanding and ManagingThe ConstraintsSystem constraints can be either physical constraints or policy constraints. Policy constraints are generally more difficult to find and eliminate, but the elimination of a policy constraint generally provides a more pronounced system improvement.2424Do. Dr. Blent SezenDo. Dr. Blent SezenUnderstanding and ManagingThe ConstraintsIdeas are not solutions. Generating ideas can be beneficial, but only if there is follow-through to develop the idea into a solution and then implement it completely. 2525Do. Dr. Blent SezenDo. Dr. Blent SezenUnderstanding and ManagingThe ConstraintsThe focus should be on balancing flow through The focus should be on balancing flow through the shop. the shop. The key is throughput that end up as sales, not on The key is throughput that end up as sales, not on throughput that may end up as inventory. throughput that may end up as inventory. Some accounting systems promote high Some accounting systems promote high production rates even if the sales are lower. production rates even if the sales are lower. 2626Do. Dr. Blent SezenDo. Dr. Blent SezenUnderstanding and ManagingThe ConstraintsUtilization of a non-bottleneck is determined Utilization of a non-bottleneck is determined by constraints in the systemby constraints in the system. . Non-bottleneck operations do not restrict system Non-bottleneck operations do not restrict system output. output. Those resources should, therefore, be managed in Those resources should, therefore, be managed in such a way as to provide maximum support for such a way as to provide maximum support for constraint resources. constraint resources. 2727Do. Dr. Blent SezenDo. Dr. Blent SezenUnderstanding and ManagingThe ConstraintsUtilization of an operation is not the same as Utilization of an operation is not the same as activationactivation. . In the TOC concept, an operation is considered In the TOC concept, an operation is considered activated only when it is providing benefit for the activated only when it is providing benefit for the entire system to give more output. entire system to give more output. The operation may be utilized, or producing The operation may be utilized, or producing material not needed until some time in the material not needed until some time in the future, but that does not necessarily help the future, but that does not necessarily help the entire system.entire system.2828Do. Dr. Blent SezenDo. Dr. Blent SezenUnderstanding and ManagingThe ConstraintsAn hour lost at a constraint operation is an hour lost to throughput for the entire process. It is for this reason that the major focus of managing and scheduling an operation is on the constraint.2929Do. Dr. Blent SezenDo. Dr. Blent SezenUnderstanding and ManagingThe ConstraintsAn hour lost at a non-constraint will not impact total throughput. It represents instead excess capacity. 3030Do. Dr. Blent SezenDo. Dr. Blent SezenUnderstanding and ManagingThe ConstraintsTransfer batches do not have to be the same size as Transfer batches do not have to be the same size as process batches, and often should not be. process batches, and often should not be. Process batches for constraints should be of a size that Process batches for constraints should be of a size that maximize the effective utilization of the process maximize the effective utilization of the process (minimize downtime). (minimize downtime). Process batches at non-constraints are not so critical. Process batches at non-constraints are not so critical. Transfer batches (the amount of material moved), may Transfer batches (the amount of material moved), may often be smaller to maximize throughput and minimize often be smaller to maximize throughput and minimize process inventories. process inventories. 3131Do. Dr. Blent SezenDo. Dr. Blent SezenUnderstanding and ManagingThe ConstraintsA schedule should be determined by using all A schedule should be determined by using all the operational constraints. the operational constraints. In many operations schedules are set sequentially. In many operations schedules are set sequentially. TOC argues that all constraint areas should be considered TOC argues that all constraint areas should be considered at the same time when making a schedule. at the same time when making a schedule. The theory also argues that lead times are a result of the The theory also argues that lead times are a result of the schedule and should not be determined before the schedule and should not be determined before the scheduling process. scheduling process. 3232Do. Dr. Blent SezenDo. Dr. Blent SezenImproving the Process using TOC PrinciplesIf a TOC approach is deemed appropriate to help improve a business system, there is a five-step process that is recommended to help improve the performance of the business. 3333Do. Dr. Blent SezenDo. Dr. Blent SezenImproving the Process using TOC Principles1.1.Identify the constraint. Identify the constraint. This implies the need to examine the entire This implies the need to examine the entire process to determine which process limits the process to determine which process limits the throughput. throughput. For example, in the example on Slide 10, For example, in the example on Slide 10, suppose the sales department was only selling suppose the sales department was only selling the product output at the rate of 3 per hour. the product output at the rate of 3 per hour. 3434Do. Dr. Blent SezenDo. Dr. Blent Sezen1.Identify the constraint. In that case, the sales department would be considered the constraint and not process 3. it must be kept in mind that a constraint limits throughput with respect to overall business sales, not merely inventory production.3535Do. Dr. Blent SezenDo. Dr. Blent SezenImproving the Process using TOC Principles2. 2. Exploit the constraint. Exploit the constraint. Find methods to maximize the utilization of the Find methods to maximize the utilization of the constraint toward productive throughput. constraint toward productive throughput. For example, in many operations all processes are For example, in many operations all processes are shut down during lunchtime or during breaks. shut down during lunchtime or during breaks. If a process is a constraint, the operation should If a process is a constraint, the operation should consider rotating lunch periods so that the consider rotating lunch periods so that the constraint is never allowed to be idle. constraint is never allowed to be idle. 3636Do. Dr. Blent SezenDo. Dr. Blent Sezen2. Exploit the constraint. Suppose, for example, an operation has a certain Suppose, for example, an operation has a certain process that represents a clear and large constraint. process that represents a clear and large constraint. Suppose also that they currently have 7 productive hours Suppose also that they currently have 7 productive hours for an 8-hour shift (30 minutes for lunch and two 15-for an 8-hour shift (30 minutes for lunch and two 15-minute breaks).minute breaks).Assuming they have multiple workers that can operate Assuming they have multiple workers that can operate the process (or can train more), they could stagger the process (or can train more), they could stagger lunch times and break times for just that one process, lunch times and break times for just that one process, allowing it to operate the full 8 hours. allowing it to operate the full 8 hours. 3737Do. Dr. Blent SezenDo. Dr. Blent SezenImproving the Process using TOC Principles3. Subordinate everything to the constraint. Effective utilization of the constraint is the most important issue. Everything else is secondary. 4.Elevate the constraint. Essentially this means to find ways to increase the available hours of the constraint, including adding more of it. 3838Do. Dr. Blent SezenDo. Dr. Blent SezenImproving the Process using TOC Principles5. 5. Once the constraint is a constraint no longer, find the Once the constraint is a constraint no longer, find the new one and repeat the steps. new one and repeat the steps. As the constraint effective utilization increases, it may As the constraint effective utilization increases, it may cease to be a constraint as another process becomes cease to be a constraint as another process becomes one. one. In that case the emphasis shifts to the new process In that case the emphasis shifts to the new process constraint. constraint. It is also possible that a sales-related change in the product It is also possible that a sales-related change in the product mix will cause a different process to become the mix will cause a different process to become the constraint. constraint. 3939Do. Dr. Blent SezenDo. Dr. Blent SezenNotes on the five steps:The third step is accomplished byReleasing material at the gateway (first processing) center at a rate that will keep the constraint busy.Prioritization of non-constraint tasks based almost exclusively on constraint needs.4040Do. Dr. Blent SezenDo. Dr. Blent SezenNotes on the five steps:The concept of exploit really implies getting the most from existing constraint resources. TOC suggests that exploiting should be maximized prior to spending additional money to acquire more of the constraint resource.4141Do. Dr. Blent SezenDo. Dr. Blent SezenNotes on the five steps:The fifth step is really a warning to continually check to ensure the constraint has not shifted. Effective exploitation of existing constraints and a shift in product mix are examples of events that can cause the constraint to shift.4242Do. Dr. Blent SezenDo. Dr. Blent SezenNotes on the five steps:After understanding these five steps, it may be After understanding these five steps, it may be helpful to consider that not all facilities operating helpful to consider that not all facilities operating in all types of business environments may find in all types of business environments may find the approach to TOC easy to implement. the approach to TOC easy to implement. For example, if an operation has a highly volatile For example, if an operation has a highly volatile product mix due to constantly shifting customer product mix due to constantly shifting customer orders for a large variety of products, they may orders for a large variety of products, they may discover that the constraint will also be volatile. discover that the constraint will also be volatile. 4343Do. Dr. Blent SezenDo. Dr. Blent SezenNotes on the five steps:At one time the mix of process requirements At one time the mix of process requirements may point to one constraint, while at another may point to one constraint, while at another time the mix may create an entirely different time the mix may create an entirely different constraint. constraint. If the constraint shifting occurs frequently, then If the constraint shifting occurs frequently, then there could be far too little opportunity to apply there could be far too little opportunity to apply the TOC approaches on one constraint before it the TOC approaches on one constraint before it shifts to another point in the process.shifts to another point in the process.4444Do. Dr. Blent SezenDo. Dr. Blent SezenImpact On Operation StrategyFor a given type and mix of products, management can For a given type and mix of products, management can elect to consciously decide where the constraint should elect to consciously decide where the constraint should be located and then proceed to develop the operational be located and then proceed to develop the operational strategy around that selected constraint. strategy around that selected constraint. Marketing and Sales can be tightly tied to the constraint. Marketing and Sales can be tightly tied to the constraint. Specifically, an analysis can be made to determine the Specifically, an analysis can be made to determine the mix of products to sell to maximize profits, and also it is mix of products to sell to maximize profits, and also it is possible to sell more of products that do not use the possible to sell more of products that do not use the constraint (implying that excess capacity is available to constraint (implying that excess capacity is available to make more of those products). make more of those products). 4545Do. Dr. Blent SezenDo. Dr. Blent SezenImpact On Operation StrategyEngineering and other process improvement activities can and should be focused on making the constraint process more efficient and effective. The company should consider if and how the non-constraint processes may be used to supplement or be used to make the constraint resources more effective. 4646Do. Dr. Blent SezenDo. Dr. Blent SezenImpact On Operation StrategyIf the company has a choice as to where the constraint is located in the process, they may elect to have the constraint early in the process. In that way the size of the required buffer needed to guard the constraint against starvation of material will be minimized. 4747Do. Dr. Blent SezenDo. Dr. Blent SezenImpact On Operation StrategyIf, on the other hand, there are processes early If, on the other hand, there are processes early in the overall process that have poor quality in the overall process that have poor quality yield, the constraint should be placed later in the yield, the constraint should be placed later in the overall process. overall process. Some processes, especially certain chemical Some processes, especially certain chemical processes, have poor yield by their very nature. processes, have poor yield by their very nature. The idea is to have those processes placed prior The idea is to have those processes placed prior to the constraint. to the constraint. 4848Do. Dr. Blent SezenDo. Dr. Blent SezenImpact On Operation StrategyI If they were placed after the constraint, then the f they were placed after the constraint, then the implication is that some product that has already implication is that some product that has already been through the constraint will not be scrapped been through the constraint will not be scrapped or need rework using the constraint. or need rework using the constraint. Since the idea behind TOC is to have all items Since the idea behind TOC is to have all items going through the constraint be turned into going through the constraint be turned into sales, clearly it is not a good idea to have sales, clearly it is not a good idea to have constraint time being wasted by being used for a constraint time being wasted by being used for a product that will later be rejected. product that will later be rejected. 4949Do. Dr. Blent SezenDo. Dr. Blent SezenLogistics and the Theory of ConstraintsLogistics deals with the physical movement of material through the production process. The Theory of Constraints has specific issues dealing with logistics, as well as some methods to deal with making logistical movement effective. 5050Do. Dr. Blent SezenDo. Dr. Blent SezenLogistics and the Theory of ConstraintsMost systems are made up of a series of dependent events, or a series of specific steps that must be followed in a correct order to complete a job. This implies that any lateness at an early station in the process will potentially impact negatively later stations in the process. 5151Do. Dr. Blent SezenDo. Dr. Blent SezenLogistics and the Theory of ConstraintsMost activities have statistical fluctuations Most activities have statistical fluctuations inherent in their operation. inherent in their operation. This implies that activity times are not This implies that activity times are not deterministic and deviations about the mean will deterministic and deviations about the mean will exist. exist. The TOC approach suggests that it is these The TOC approach suggests that it is these statistical fluctuations that make traditional statistical fluctuations that make traditional assembly line balancing approaches impractical. assembly line balancing approaches impractical. 5252Do. Dr. Blent SezenDo. Dr. Blent SezenLogistics and the Theory of ConstraintsThere are often three reasons given for a loss of throughput, and these reasons are focused on the constraint in the system. 5353Do. Dr. Blent SezenDo. Dr. Blent Sezenthree reasons for a loss of throughput1. The constraint is broken. Since no excess capacity exists on a constraint, the loss of capacity will directly result in a loss of throughput for the entire business. 5454Do. Dr. Blent SezenDo. Dr. Blent Sezen1. The constraint is broken. One major solution to this potential problem is a good One major solution to this potential problem is a good program of preventive maintenance. program of preventive maintenance. Such a program needs to be scheduled and managed Such a program needs to be scheduled and managed carefully, for even preventive maintenance represents a carefully, for even preventive maintenance represents a use of capacity for the constraint. use of capacity for the constraint. In general, this situation is compatible with a basic principle In general, this situation is compatible with a basic principle of maintenance the higher the cost of an unscheduled of maintenance the higher the cost of an unscheduled breakdown of a process, the more critical the following of breakdown of a process, the more critical the following of a well-designed preventive maintenance program. a well-designed preventive maintenance program. 5555Do. Dr. Blent SezenDo. Dr. Blent Sezen1. The constraint is broken. This is the same basic issue we found with a lean This is the same basic issue we found with a lean production system. production system. Without much inventory in the system, processes Without much inventory in the system, processes tend to be tightly linked, and the loss of any tend to be tightly linked, and the loss of any operation will quickly bring the entire system operation will quickly bring the entire system down. down. Maintenance becomes important for TOC for Maintenance becomes important for TOC for roughly the same reason as for lean production roughly the same reason as for lean production systems - the potential high cost of a drop in systems - the potential high cost of a drop in throughput for the entire system.throughput for the entire system.5656Do. Dr. Blent SezenDo. Dr. Blent Sezenthree reasons for a loss of throughput2. 2. The constraint is starved. The constraint is starved. In this condition, there is no inventory from the preceding In this condition, there is no inventory from the preceding processes available for work by the constraint. processes available for work by the constraint. The constraint is capable of production, but cannot produce The constraint is capable of production, but cannot produce without material to work on. without material to work on. The solution to this problem is using a buffer in front of the The solution to this problem is using a buffer in front of the constraint. The buffer is inventory released early into the constraint. The buffer is inventory released early into the system.system.5757Do. Dr. Blent SezenDo. Dr. Blent Sezenthree reasons for a loss of throughput3. 3. The constraint is blocked. The constraint is blocked. In this condition, the constraint is available and In this condition, the constraint is available and there is material available on which to work, but there is material available on which to work, but there is no physical space in which to place the there is no physical space in which to place the completed units. completed units. The solution to this potential problem is to have a The solution to this potential problem is to have a space buffer available after the constraint in the space buffer available after the constraint in the process in which to place production completed process in which to place production completed by the constraint operation. by the constraint operation. 5858Do. Dr. Blent SezenDo. Dr. Blent SezenScheduling and the Theory of ConstraintsThe scheduling system developed for the Theory of Constraints has its own specific approach, although fairly closely related to a pull system inherent with lean production. It is of ten described as drum-buffer-rope. 5959Do. Dr. Blent SezenDo. Dr. Blent SezenScheduling and the Theory of ConstraintsDrumDrum The drum of the system refers to the drumbeat The drum of the system refers to the drumbeat or pace of production. or pace of production. Essentially, it represents the master schedule for Essentially, it represents the master schedule for the operation, which is focused around the pace the operation, which is focused around the pace of throughput of throughput as defined by the constraint. as defined by the constraint. 6060Do. Dr. Blent SezenDo. Dr. Blent SezenDrumPut in other terms, the drum can simply be considered as the work schedule of the organizations constraint. In order for the organization to take full advantage of this knowledge, it must be assumed that all non-constraint functions understand this drumbeat schedule and provide total support. 6161Do. Dr. Blent SezenDo. Dr. Blent SezenScheduling and the Theory of ConstraintsBufferBuffer Since it is so important that the constraint never Since it is so important that the constraint never be starved for needed inventory, a time buffer be starved for needed inventory, a time buffer is often established in front of the constraint. is often established in front of the constraint. The idea is to protect the system from normal The idea is to protect the system from normal variations and thereby protect the constraint variations and thereby protect the constraint from disruptions or material starvation. from disruptions or material starvation. 6262Do. Dr. Blent SezenDo. Dr. Blent SezenBufferEven though the buffer manifests itself as inventory Even though the buffer manifests itself as inventory released into the system, the product mix of this material released into the system, the product mix of this material can be very different based on the schedule. can be very different based on the schedule. Since it is not based on specific inventory of specific Since it is not based on specific inventory of specific products or components, it is generally called a time products or components, it is generally called a time buffer. buffer. This is a key difference in the conceptual use of a time This is a key difference in the conceptual use of a time buffer instead of an inventory buffer-the time buffers tend buffer instead of an inventory buffer-the time buffers tend to be largely immune to (protected from) variations in to be largely immune to (protected from) variations in product mix. product mix. 6363Do. Dr. Blent SezenDo. Dr. Blent SezenBufferAs an example, suppose variations in As an example, suppose variations in processing and the probability of some processing and the probability of some disruptions in operations upstream from the disruptions in operations upstream from the constraint could mean that material could be constraint could mean that material could be held up“ for as much as 4 hours. held up“ for as much as 4 hours. The implication, then, would be that based on The implication, then, would be that based on the processing schedule at the constraint the the processing schedule at the constraint the material for constraint processing would be material for constraint processing would be released into the first operation 4 hours earlier released into the first operation 4 hours earlier than the normal. than the normal. 6464Do. Dr. Blent SezenDo. Dr. Blent SezenScheduling and the Theory of ConstraintsRopeRopeThe analogy is that the rope pulls production to the The analogy is that the rope pulls production to the constraint for necessary processing. constraint for necessary processing. While this may imply a Kanban-type pull system, it can While this may imply a Kanban-type pull system, it can be done by a well-coordinated release of material into be done by a well-coordinated release of material into the system at the right time. the system at the right time. As can be seen, even the scheduling system has its As can be seen, even the scheduling system has its primary focus on effective management of the primary focus on effective management of the organizations constraint to throughput and sales.organizations constraint to throughput and sales.6565Do. Dr. Blent SezenDo. Dr. Blent SezenMultiple-time BuffersTime buffers are used to make sure the Time buffers are used to make sure the constraint is not starved, but other time buffers constraint is not starved, but other time buffers are also necessary. An example may help to are also necessary. An example may help to illustrate: illustrate: Suppose you have a product made from three Suppose you have a product made from three components. components. Component 1 is processed from raw material Component 1 is processed from raw material and then assembled with component 2 after it is and then assembled with component 2 after it is processed from raw material. processed from raw material. 6666Do. Dr. Blent SezenDo. Dr. Blent SezenMultiple-time Buffers6767Do. Dr. Blent SezenDo. Dr. Blent SezenMultiple-time BuffersThe subassembly is then assembled with The subassembly is then assembled with component 3 after it is processed from raw component 3 after it is processed from raw material. material. The final product is then shipped to the The final product is then shipped to the customer. customer. The constraint in the system is located in the The constraint in the system is located in the middle of the processing for component 1. middle of the processing for component 1. 6868Do. Dr. Blent SezenDo. Dr. Blent SezenMultiple-time BuffersOnce component 1 has been processed on the Once component 1 has been processed on the constraint, its value to the system has risen constraint, its value to the system has risen significantly because constraint time has been significantly because constraint time has been invested. invested. Nothing should, therefore, impede the progress Nothing should, therefore, impede the progress of component 1. of component 1. The problem could arise, however, that The problem could arise, however, that component 1 will arrive at the Assembly 1 area component 1 will arrive at the Assembly 1 area before component 2 because of some problem before component 2 because of some problem with component 2. with component 2. 6969Do. Dr. Blent SezenDo. Dr. Blent SezenMultiple-time BuffersSince we would never want constraint-invested material Since we would never want constraint-invested material to wait for non-constrained material, we should stage a to wait for non-constrained material, we should stage a time buffer of material for component 2 before the time buffer of material for component 2 before the Assembly 1 area. Assembly 1 area. This is done by releasing it earlier-the amount earlier This is done by releasing it earlier-the amount earlier depending on the time buffer based on the time estimate depending on the time buffer based on the time estimate needed to overcome any unanticipated shock in the needed to overcome any unanticipated shock in the system. system. In this case the time buffer is called an assembly time In this case the time buffer is called an assembly time buffer, as opposed to the time buffer before the buffer, as opposed to the time buffer before the constraint, which is usually called a constraint time constraint, which is usually called a constraint time buffer.buffer.7070Do. Dr. Blent SezenDo. Dr. Blent SezenMultiple-time BuffersThe same argument applies to the Assembly 2 The same argument applies to the Assembly 2 area. area. The subassembly from components 1 and 2 The subassembly from components 1 and 2 have constraint time invested, so we would not have constraint time invested, so we would not want them waiting for component 3. want them waiting for component 3. This calls for another assembly time buffer to be This calls for another assembly time buffer to be generated at the Assembly 2 area. generated at the Assembly 2 area. Unfortunately, the need for buffers has not been Unfortunately, the need for buffers has not been fulfilled. fulfilled. 7171Do. Dr. Blent SezenDo. Dr. Blent SezenMultiple-time BuffersI It is possible that the final product with its t is possible that the final product with its constraint-invested material could be held up at constraint-invested material could be held up at shipping, since the processes that take place shipping, since the processes that take place between assembly and shipping have not been between assembly and shipping have not been part of the protection. part of the protection. This implies an additional time buffer before the This implies an additional time buffer before the shipping area, referred to as a shipping area, referred to as a shipping time shipping time buffer. buffer. 7272Do. Dr. Blent SezenDo. Dr. Blent SezenMultiple-time Buffers7373Do. Dr. Blent SezenDo. Dr. Blent SezenControl Points and BatchesAll this discussion regarding buffers and scheduling may start one to think that the scheduling using TOC approaches are more difficult and complex than standard approaches. That does not need to be the case. 7474Do. Dr. Blent SezenDo. Dr. Blent SezenControl Points and BatchesBased on the flow of material and the type of Based on the flow of material and the type of operation, there are specifically defined types of operation, there are specifically defined types of control points that may be important for TOC control points that may be important for TOC scheduling, measurement and control. scheduling, measurement and control. A control point is a point in the process where A control point is a point in the process where measures are taken and decisions made based measures are taken and decisions made based on those measures. on those measures. Typical control points for TOC include: Typical control points for TOC include: 7575Do. Dr. Blent SezenDo. Dr. Blent SezenControl Points and BatchesThe constraint-The constraint- this this is clearly the most critical control is clearly the most critical control point, and needs to be scheduled carefully based on point, and needs to be scheduled carefully based on sales.sales.The first operation (or the gateway)The first operation (or the gateway) - it is quite important - it is quite important to release the right material at the right time into the to release the right material at the right time into the system so it will reach the constraint. This is, in effect, system so it will reach the constraint. This is, in effect, the rope of the drum-buffer-rope system.the rope of the drum-buffer-rope system.Diverging points-Diverging points- these these points are where a common part points are where a common part can be processed into one of several different options. can be processed into one of several different options. They must be managed to ensure that material, They must be managed to ensure that material, especially constraint material, is used in the correct especially constraint material, is used in the correct manner for the correct assembly. manner for the correct assembly. 7676Do. Dr. Blent SezenDo. Dr. Blent SezenControl Points and BatchesConverging points-Converging points- these these are really assembly are really assembly operations where material from non-constraint operations where material from non-constraint operations is combined with constraint material operations is combined with constraint material to produce an assembly or subassembly. to produce an assembly or subassembly. it is important to manage these points to make sure it is important to manage these points to make sure constraint material is not held up from being constraint material is not held up from being processed.processed.The buffers-The buffers- these indude constraint buffers, these indude constraint buffers, assembly buffers, and shipping buffers as assembly buffers, and shipping buffers as described earlier. described earlier. 7777Do. Dr. Blent SezenDo. Dr. Blent SezenControl Points and BatchesTOC also recognizes there can be fundamental TOC also recognizes there can be fundamental differences between differences between process batchesprocess batches ( (the amount the amount of material produced at an operation for a given setupof material produced at an operation for a given setup) ) and and transfer batchestransfer batches ( (the amount of material moved the amount of material moved from one operation to the next operationfrom one operation to the next operation). ). In general, process batches should be fairly In general, process batches should be fairly large for constraint operations in order to large for constraint operations in order to minimize the time lost for setups. minimize the time lost for setups. 7878Do. Dr. Blent SezenDo. Dr. Blent SezenControl Points and BatchesProcess batches for non-constraints are largely irrelevant since those operations will have excess capacity. Transfer batches, on the other hand, should be fairly small to minimize work-in-process inventory levels. 7979Do. Dr. Blent SezenDo. Dr. Blent Sezen结束结束