STORAGE: CONSIDERATIONS ON THE PICKING ACTIVITY

The main factor to be attributed to the evolution of storage in the world in the last two decades was the increase in customer demand. A recent study on automation in the warehousing area analyzed the distribution centers of three large companies in Brazil – Chocolates Garoto, Souza Cruz and Lojas Americanas – and identified the improvement in service and/or product quality as the main driver of their investments in this area. area.

Another periodic survey indicates that frequency and delivery time are among the three main service dimensions evaluated by retailers. The importance given to these two dimensions is related to programs to reduce inventory levels – such as JIT (just in time), QR (quick response) and continuous replenishment – ​​whose foundations are supported by increasing the frequency and reducing the lead time. delivery.

In addition, the great proliferation of the number of products – resulting not only from the launch of new products, but also from the wide variety of models, colors and packaging – and the growing increase in direct deliveries to the consumer – as a result of sales through catalogs, over the internet , over the phone, or even through stores that started to work only with merchandise on display – also brought new demands to storage operations.

In response to these challenges, companies are restructuring their warehousing operations to accommodate an increase in the number of orders (resulting from increased delivery frequency and direct-to-consumer delivery), a greater variety of items (due to the proliferation of the number of products) in a shorter time (result of shortening the delivery period). Thus, finished product warehouses for the purpose of storing goods are giving way to distribution centers, whose main focus is on the picking activity.

The increased importance of the picking activity has led to new investments being made in this area, mainly in sorting systems. To have an idea of ​​the representativeness of the costs of this activity, on average, picking is responsible for 60% of the costs of a distribution center.

Within this context, this article will address the picking activity, clarifying some questions about three important planning decisions. The first refers to the separation of an area of ​​the distribution center just for picking, regardless of storage. The second concerns the organization of work. The third decision involves the selection of technologies to be adopted. Finally, two challenges arising from new technologies available, recently disseminated, will be addressed, the first referring to the A-Frame and the second to picking by-light.

THE SEPARATION OF THE PICKING AREA FROM THE STORAGE AREA

The storage area in most warehouses occupies a relatively large space, due to the storage of stocks. Thus, the separation of orders carried out in this area may imply large displacements by operators.

Figure 1 shows the relative time consumption of an operator picking in the storage area. This graph indicates that an operator consumes 50% of his time just moving around the storage area.

However, there are some intermediate alternatives to reduce this time spent traveling. Among these, the following stand out:

• Algorithms for defining collection routes, which minimize the average distance traveled in order picking;
• alternative methods of work organization (which will be dealt with later) with the aim, for example, of collecting more orders for each trip;
• addressing logic that positions the products in the storage area using criteria that minimize the average distance of movement, considering the number of shipments of each item, its volume in stock and the complementarity between the items (that is, keeping the products that are usually shipped together).

In addition, the identification of the collection addresses and the clear and objective provision of information (documentation, instructions and labels) are also important points to streamline the operator's tasks.

Even considering the use of all the measures presented, the complexity of picking makes it necessary to separate a warehouse area dedicated to this activity. Among the drivers used to define the degree of complexity, the following stand out: the size of the picking units, the number of orders shipped per day, the variety of items and the time available for picking an order.

According to the size of the separation units – which considers the smallest unit – there are five basic categories:

• pallet picking – when the smallest picking unit is the pallet. In this case, orders never contain pallet fractions of certain products, only closed pallets;
• separation of pallet layers – in this case the smallest unit of separation is a set of boxes, which form a layer of the pallet;
• box sorting – when the smallest sorting unit is closed boxes;
• separation of fractioned boxes – this is the case in which the boxes need to be opened to handle the packages that make up the box;
• separation of items – more fractional alternative where individual items of certain products are handled.

The more fractional the separation, the greater the number of orders shipped per day, the greater the variety of items and the shorter the available time, the more complex the operation will be considered. In addition to the complexity affecting the performance and productivity of picking, it also compromises the precision in filling the order, in view of the increased possibility of errors that makes verification difficult.

The option for the dedicated area for picking activity allows a wide range of goods to be arranged in a relatively small area, so that the operator does not need to travel long distances in his displacement.

The area dedicated to picking, however, creates a new demand: the resupply of items on the picking line. In more critical cases, where product turnover on the line is very high, it is necessary to create an intermediate stock area between storage and picking, called reserve stock. This area has the task of quickly resupplying the picking line, since it must operate with a low inventory level and without product shortages to ensure line speed and minimize the risk of downtime.

Work Organization Methods

In order to improve picking productivity, some work organization methods were developed (figure 2) with the aim of minimizing non-useful times, spent on operators moving around and searching for products. These methods consider the number of operators responsible for picking each order and the number of orders collected simultaneously by the same operator. The three basic methods are presented below:

• Discrete picking – in which each operator collects one order at a time, picking the order line by line. This form of organization is widely used for its simplicity. The propensity for errors is relatively small, as it handles one order at a time. Its major disadvantage is low productivity, due to the excessive time spent traveling with the operator.
• picking by zone – in this method the warehouse is segmented into sections or zones and each operator is associated with a zone. Thus, each operator collects the order items that are part of its section, leaving them in a consolidation area, where the items collected in different zones are grouped, composing the original order. This method is often used. Among its advantages is the flexibility of allowing different handling and storage equipment to be used. Thus, while one zone operates with pallet separation, the other can handle boxes. This organization tends to be more productive than discrete picking, as it allows for less operator displacement. Its great difficulty is balancing the workload between the different zones.
• batch picking – in this method, each operator collects a group of orders together, instead of picking only one order at a time. Thus, when going to the storage location of a given product, the operator collects the number of items that satisfy his set of orders. This method enables high productivity when orders have little variety of items (up to 4 items) and are small in terms of volume. Its great advantage is to minimize the operator's travel time, as in a single trip he collects a set of orders, reducing the average displacement per order. The disadvantage of this method focuses on the risks of errors in the separation and ordering of orders.

In addition to the three methods presented, the use of wave picking is common. In this, several schedules are carried out per shift, so that orders must be collected at specific times of the day. Wave picking is used in conjunction with the methods presented and its advantage is that it allows for greater integration of picking with the dispatch area, through programming the time of collection and shipment of each order.

The picking method used can be a combination of those presented. Zone picking can be used with batch picking or wave picking, or even both simultaneously. Normally, these combinations enable an increase in productivity, but also require greater control.

Regardless of the method used, concern for ergonomics is fundamental. Incentives for productivity and accuracy should also be considered as important instruments in the search for separation performance.

Picking Systems

There is a wide range of systems developed for picking activities and their choice must consider the specific characteristics of the operation (such as variety of items, size of picking units and operating speed) and the products handled (such as weight, shape and grade). of fragility), in addition to tolerance for separation errors and available budget.

Before dealing with picking systems, it is essential to present an important piece of equipment used in this activity, the flow-rack (figure 3). This equipment can be used both in the separation of boxes and units. Its operation is similar to the soda can cooler in a convenience store. The boxes can be supplied by the rear part of the equipment and collected by its front part, and removing the first box causes the others to slide forward.

Due to its low cost and its great functionality, the flow-rack has become a very widespread piece of equipment, and can be used with or without coupled handling equipment, as well as in conjunction with sophisticated picking systems.

The five main picking systems are presented below:

A-Frame

A-Frame (figure 4) is a high productivity system capable of separating hundreds of orders in a short time, with great precision and with a reduced staff. This is a modular system, made up of a conveyor belt, on which there is a structure composed of a series of channels that cover both sides of the belt. Each channel works with a certain SKU, having the capacity to store several units, which are stacked in their respective structure.

The A-Frame command system controls the ejection of products from each channel on the conveyor belt and each section of the conveyor belt is associated with a particular order. At the end of the line, the products are automatically transferred to boxes and transported to the other picking areas, or directly to the shipping area, if the order is complete.

Several A-Frame modules can be used – both in series and in parallel – to increase system capacity. Furthermore, this technology can also be used in conjunction with other separation systems. This type of system allows a very fast separation with high productivity, however it has some restrictions on use related to the fragility and/or format of the handled items.

Carousel

The carousels (figure 5) are rotational, vertical or horizontal equipment that pack the products with the function of bringing them to the operator, eliminating the times associated with their displacement and the search for products. The main advantage of this system is that it allows operation with a wide variety of items. In addition, the vertical carousel also allows a good use of space by taking advantage of the right foot of the building. Its main disadvantage is related to the relatively slow collection speed, which often makes it not recommended.

Automatic storage and collection systems

Automatic storage and collection systems (AS/RS) capable of operating with more fractional handling units are known as miniload (figure 6). However, even miniloads are capable of operating only with boxes, or large volume items. Its operation is very similar to that of the stacker crane (unit load).

Among the main advantages of the miniload, its accuracy and speed can be highlighted, as well as the potential to operate with a wide variety of items. Among the disadvantages are the high cost of implementation and maintenance, and the lack of flexibility of these systems.

The radio frequency separation

This type of system relies on radio frequency communication to assist the operator in collecting items. For this, the operator uses a hand terminal or a terminal attached to the arm (figure 7) which always indicates the address of the next product and the number of units to be collected. When collecting items, the operator reads the bar code of the products, through the manual terminal, which checks the collection and indicates the address of the next product to be collected.

This type of technology is being widely used in Brazil due to its low cost and high flexibility. Its major disadvantage is related to its performance, which is limited by the operator's displacement speed.

The by-light picking system

This system reconciles performance and flexibility, making it one of the most widespread systems in Brazil. Picking by-light (figure 8) integrates the use of conveyor belts, optical readers and sensors with traditional flow rack structures handled by operators.

The good performance of this system is obtained by placing the products around the employees, who only collect the products from their workstation, not having to move around or move the order boxes that are transported automatically by means of a conveyor belt. . In addition, the digital displays of each flow-rack position automatically indicate the location and number of units to be collected, making picking list unnecessary, which speeds up the picking process for operators.

Flexibility is the result of the operators' participation in handling, which in addition to considering the specific characteristics of each product, including fragility, can simultaneously collect and organize the products in the delivery boxes.

THE NEW PICKING TECHNOLOGIES AND ITS NEW CHALLENGES

The search for greater productivity, speed and precision in picking orders leads companies to implement new technologies in the picking area. However, the simple adoption of technology does not guarantee these operational improvements, but serves as a tool that enables the development of new processes. It should be noted that many of these new processes would not even exist without this technological support.

Many companies are implementing sophisticated separation systems without support from other support and control systems. Support and decision support systems are complementary to the workforce, procedures and handling equipment and become vital within the picking operation.

Within this context, one can mention picking systems as technological tools that enable the architecture of new processes, capable of providing large gains in efficiency. To succeed in implementing a new process, however, it is essential to develop communication systems and train work teams for the operation.

Each company has its particularities with regard to its need for separation, due to the profile of its customers' orders and its product portfolio. On the other hand, separation systems have a nominal capacity that can only be achieved in real terms given a series of assumptions. To illustrate these situations, challenges related to the implementation of new A-frame and picking-by-light technologies will be presented below.

As for the A-Frame system

This is one of the picking systems that has one of the best performances in terms of picking speed. However, several constraints must be satisfied for its speed to be maximized. Among them, two can be highlighted: no order can have many units of the same item and the resupply of the line has to be fast enough so that the product channel does not become empty.

As it is not feasible to limit the demand for a certain product in each order, the solution ends up being the placement of a product in more than one channel. As for resupply, normally a flow rack line is coupled alongside the A-Frame with operators dedicated to this activity. These solutions may seem simple, but in reality they open up a large number of decisions.

To complicate matters, these decisions must be made on an almost daily basis to meet wide variations in SKU demand. Among the necessary decisions, it is worth mentioning: controlling the number of channels that will be made available for each product and the positioning of all products, given the restrictions not only of the line, but also of resupply.

Regarding the by-light picking system

To maximize picking performance with this system, the picking line must have a well-balanced workload between its stations and the products with the highest number of movements must be located in positions that are most easily accessible to operators. Balancing the workload is vital for this type of system, as each employee is responsible for a workstation and the formation of queues at the stations can result in the stoppage of the entire line.

Another requirement of great influence on the productivity of the line is the positioning of the products according to the number of movements, since the different positions of the station (flow rack addresses) present different handling difficulties, depending on the height and distance from the hands of the operator.

The physical characteristics of the products – the shape, weight and size – form a third factor – in addition to the demand and the positioning of the products – that influences the workload of each season, since the difficulty of handling each product will affect their respective separation time.

The great difficulty is that, as a rule, the demand for each item undergoes constant fluctuations due to seasonal factors, its stage in the life cycle and the company's marketing actions, in addition to other external factors. In this way, the allocation of products to the positions, that is, line balancing must be carried out periodically to ensure the monitoring of the demand curve, maintaining its effectiveness.

In order for product changes to take place on the line, the line must be stopped, as the system that lights up the digital displays works according to the position of each product. In addition, the physical replacement of products can also affect the resupply system. Therefore, it is important to always minimize the number of replacements in a balancing.

CONCLUSION