Acknowledgments
Lemma 1: Properties of K-convex functions
7.2 Ten Principles of Material Handling
The 10 principles of material handling developed by the Material Handling Industry of America are:
planning, standardization, work, ergonomics, unit load, space utilization, system, automation, environ-mental, and life cycle. A multimedia education CD explaining various aspects of the 10 principles is available upon request (see [3]).
7.2.1 Planning
A material handling plan is a prescribed course of action that specifies the material, moves, and the method of handling in advance of implementation. Four key aspects need to be considered in develop-ing a sound material handldevelop-ing plan.
1. The communication between designers and users is very important in developing the plans for operations and equipments. For large-scale material handling projects, a team including all stakeholders is required.
2. The material handling plan should incorporate the organization’s long-term goals and short-term requirements.
3. The plan must be based on existing methods and problems, subject to current physical and economic constraints, and meet organizational requirements and goals.
4. The plan should build in flexibility so that sudden changes in the process can be assimilated.
7.2.2 Standardization
Standardization is a way of achieving uniformity in the material handling methods, equipment, controls and software without sacrificing needed flexibility, modularity, and throughput. Standardization of mate-rial handling methods and equipment reduces variety and customization. This is a benefit so long as overall performance objectives can be achieved. The key aspects of achieving standardization are as follows:
1. The planner needs to select methods and equipment that can perform a variety of tasks under a variety of operating conditions and anticipate changing future requirements. Therefore, the methods and equipment can be standardized at the same time ensuring flexibility. For example, the conveyor system in Figure 7.1 can carry different sizes of parcels.
2. Standardization can be applied widely in material handling methods, such as the sizes of contain-ers and other characteristics, as well as operating procedures and equipment.
3. Standardization, flexibility, and modularity need to complement each other, providing compatibility.
7.2.3 Work
Material handling work is equal to the product of material handling flow (volume, weight, or count per unit of time) and distance moved. It should be minimized without sacrificing productivity or the level of service required of the operation. The work can be optimized from three aspects:
1. Combine, shorten, or eliminate unnecessary moves to reduce work. For example, in dual command storage and retrieval cycles, two commands, storage or retrieval, are executed in one trip so it has less work than single storage and retrieval cycles.
2. Consider each pick-up and set-down or placing material in and out of storage as distinct moves and components of distance moved.
3. Material handling work can be simplified and reduced by efficient layouts and methods (Fig. 7.2). Gravitational force is used to reduce material handling work.
FIGuRE 7�1 Conveyor system. (Courtesy of Vanderlande Industries, The Netherlands. With permission.)
FIGuRE 7�2 Gravity roller conveyor. (Courtesy of Sunderesh S. Heragu, 10 Principles of Materials Handling, CD. With permission.)
7.2.4 Ergonomics
Ergonomics is the science that seeks to adapt work and working conditions to suit the abilities of the worker. It is important to design safe and effective material handling operations by recognizing human capabilities and limitations.
1. Select equipment that eliminates repetitive and strenuous manual labor and that the user can operate effectively. Equipment specially designed for material handling is usually more expensive than standard equipment. But using standard equipment will result in fatigue, hurt particular parts of the worker’s body, and result in error and low-operating efficiency. Therefore, it may be necessary to select specialized equipment to minimize long-term costs and injury.
2. In material handling systems, ergonomic workplace design and layout modification, it is important to pay more attention to the human physical characteristics. For example, in Figure 7.3 the work-place design on the left does not provide toe space for the worker, requiring him or her to bend forward. Maintaining this posture will produce fatigue and injury. The modified workplace with toe space is more comfortable for the worker because his or her body is in an erect position (see right side in Fig. 7.3).
3. The ergonomics principle embraces both physical and mental tasks. For example, when a printed label or message must be read quickly and easily, the plain and simple type font should be chosen preferentially. Less familiar designs and complex font may result in errors, especially when read in haste. Aesthetic fonts are poor choices. Obviously, extremes like Old English should never be used. In one word, keep it simple.
4. Safety is the priority in workplace and equipment design.
7.2.5 Unit Load
A unit load is one that can be stored or moved as a single entity at one time, regardless of the number of individual items that make up the load. When unit load is used in material flow, the following key aspects deserve attention:
FIGuRE 7�3 Modified work place. (From DeLaura, D. and Kons, D., Advances in Industrial Ergonomics and Safety II, Taylor & Francis, 1990. With permission.)
1. Less effort and work are required to collect and move a unit load than to move many items one at a time. But this does not mean bigger unit load size is always better. As the unit load size increases, the total transportation cost decreases. This decrease is offset by the increase in the inventory cost.
Figure 7.4 shows the relationship between the two.
2. Load size and composition may change as material and product move through various stages of manufacturing and the resulting distribution channels.
3. Large unit loads of raw material are common before manufacturing and also after manufacturing when they constitute finished goods.
4. During manufacturing, smaller unit loads, sometimes just one item, yield less in process inven-tory and shorter item throughput times. From Little’s law [4], when a system has reached steady state, the average number of parts in the system is equal to the product of the average time per part in the system and its arrival rate.
5. Smaller unit loads are consistent with manufacturing strategies that embrace operational objec-tives such as flexibility, continuous flow, and just-in-time delivery.
7.2.6 Space Utilization
A good material handling system should try to improve the effectiveness and efficiency of all the avail-able space. There are three key points for this principle.
1. In work areas, eliminate cluttered, unorganized spaces and blocked aisles. For example, blocked aisles will add more material flow work. In Figure 7.5, the product on the floor will force the fork-lift to pick the product on the shelf using a longer material flow path, while the storage in Figure 7.6 will result in inefficient use of vertical storage space (called honeycombing loss).
2. In storage areas, the objective of maximizing storage density must be balanced against accessi-bility and selectivity. If items are going to be in the warehouse for a long time, storage density is an important consideration. If items enter and leave the warehouse frequently, their accessibility and selectivity are important. If the storage density is too high to access or select the stored product, high storage density may not be beneficial.
3. A Cube per Order Index (COI) storage policy is often used in a warehouse. COI is a storage policy in which each item is allocated warehouse space based on the ratio of its storage space require-ments (its cube) to the number of storage/retrieval transactions for that item. Items are listed in a
Total Cost Holding Cost
Transportation Cost
11.24 Unit Load Size
11.12 22.36 Cost
FIGuRE 7�4 Trade-off between unit load and inventory costs. (Courtesy of Sunderesh S. Heragu, 10 Principles of Materials Handling, CD. With permission.)
nondecreasing order of their COI ratios. The first item on the list is allocated to the required num-ber of storage spaces that are closest to the input/output (I/O) point; the second item is allocated to the required number of storage spaces that are next closest to the I/O point, and so on. Figure 7.7 shows an interactive “playspace” in the “10 Principles of Materials Handling” CD that allows a learner to understand the fundamental concepts of the COI policy.
7.2.7 System
A system is a collection of interdependent entities that interact with each other. The main components of the supply chain are suppliers, manufacturers, distributions, and customers. The activities to support material handling both within and outside a facility need to be integrated into a unified material han-dling system. The key aspects of the system principle are:
1. At all stages of production and distribution, minimize inventory levels as much as possible.
2. Even though high inventory allows a company to provide a higher customer service level, it can also conceal the production problems which, from a long-term point of view, will hurt the company’s operations. These problems can eventually result in low production efficiency and high product cost.
3. Information flow and physical material flow should be integrated and treated as concurrent activities. The information flow typically follows material flow.
FIGuRE 7�5 Retrieving material in blocked aisles. (Courtesy of Sunderesh S. Heragu, 10 Principles of Materials Handling, CD. With permission.)
FIGuRE 7�6 Honeycombing loss. (Courtesy of Sunderesh S. Heragu, 10 Principles of Materials Handling, CD.
With permission.)
4. Materials must be easily identified in order to control their movement throughout the supply chain. For example, bar coding is the traditional method used for product identification. Radio frequency identification (RFID) uses radio waves to automatically identify people or objects as they move through the supply chain. Due to two unique product identification mandates, one from the private sector (Wal-Mart) and another from the public sector (Department of Defense), RFID has become very popular in recent years. The big difference between the two automatic data capture technologies is that bar codes is a line-of-sight technology. In other words, a scanner has to “see” the bar code to read it, which means people usually have to orient the bar code toward a scanner for it to be read. RFID tags can be read as long as they are within the range of a reader even if there is no line of sight. Bar codes have other shortcomings as well.
If a label is ripped, soiled, or falls off, there is no way to scan the item. Also, standard bar codes identify only the manufacturer and product, not the unique item. The bar code on one milk carton is the same as every other, making it impossible to identify which one might pass its expiration date first. RFID can identify items individually.
5. Meet customer requirements regarding quantity, quality, and on-time delivery and fill orders accurately.
Product Class A Product Class B Product Class C Product Class D Total
PLA Y.
box 1
class A box 2
class A box 3
class A box 4
class A
Arrange the boxes so that the total cost of moving the items in and out of the warehouse via the input/output point is minimized.
Optimum Material Handling Cost = 950.00
Total Material Movement Cost = 1171.67
Box 12 3 4 5 6 7 8 910 11 12 13 14 15 16
11 1 1 1
2 3
2 2 33 4 4 4 4 4 4
54 4 5 4 3 4 32 2 3 2 1 1 2 Class Distance box 5
class A box 6
class B box 7
class B box 8
class B
box 9
class C box 10
class C box 11
class D box 12
class D
box 13
class D box 14
class D box 15
class D
input/output point
< modify parameters
box 16 class D
16 5
Number of Boxes Cost Frequency
3 2 6
1 1 1 1
100 80 120 90
FIGuRE 7�7 Example of COI policy. (Courtesy of Sunderesh S. Heragu, 10 Principles of Materials Handling, CD.
With permission.)
7.2.8 Automation
Automation in a material flow system means using electro-mechanical devices, electronics and com-puter-based systems with the result of linking multiple operations to operate and control production and service activities. These automated devices and systems are usually controlled by programmed instructions. Automation enables equipment or systems to run with little or no operator intervention. It improves safety, operational efficiency, consistency, and predictability, while increasing system respon-siveness. Automation also decreases operating costs. In order to make the automation serve the material flow system properly, the following key aspects should be considered:
1. Simplify pre-existing processes and methods before installing mechanized or automated systems.
2. Consider computerized material handling systems where appropriate for effective integration of material flow and information management.
3. In order to automate handling, items must have features that accommodate mechanization.
4. Treat all interface issues in the situation as critical to successful automation.
7.2.9 Environmental
The environmental principle in material handling involves designing material handling methods and selecting and operating equipment in a way that preserves natural resources and minimizes adverse effects on the environment coming from material handling activities. The following three key aspects need to be considered:
1. Design containers, pallets, and other products used in material handling so they are reusable and/
or biodegradable. For example, use recyclable pallets.
2. By-products of material handling should be considered in the system design.
3. Give special handling considerations to hazardous material handling.
7.2.10 Life Cycle
Life cycle costs include all cash flows that occur between the time the first dollar is spent on the material handling equipment or method until its disposal or replacement. Its key aspects are:
1. Life cycle costs in material handling system include: capital investment; installation, setup, and equipment programming; training, system testing, and acceptance; operating, maintenance, and repair; and recycle, resale, and disposal.
2. Plan for preventive, predictive, and periodic maintenance of equipment. Include the estimated cost of maintenance and spare parts in the economic analysis. There are three types of equipment failures that occur over the equipment’s useful life—early failures when the product is being debugged, constant failures associated with the normal use of equipment, and increasing failure rate during the wear-out stage, when products fail due to aging and fatigue. A sound maintenance pro-gram will postpone the wear-out period and extend the useful life of equipment. Maintenance cost should be considered in the life cycle.
3. Prepare a long-range plan for equipment replacement.
4. In addition to measurable cost, other factors of a strategic or competitive nature should be quanti-fied when possible.
The 10 principles are vital to material handling system design and operation. Most are qualitative in nature and require the industrial engineer to employ these principles when designing, analyzing, and operating material handling systems.