Solutions for precision storage and retrieval

Citation

(1998), "Solutions for precision storage and retrieval", Industrial Robot, Vol. 25 No. 1. https://doi.org/10.1108/ir.1998.04925aaf.001

Solutions for precision storage and retrieval

Solutions for precision storage and retrieval

The family of precision storage and retrieval applications, also known as "stocking" applications, is used in many industries, ranging from wafers to disks, from pharmaceuticals to consumables, and basically anything small that needs to be stored for on-demand use.

A typical stocking application is the handling of cassettes of wafers during the wafer manufacturing process. In this application, cassettes are presented to a stocking system at several different stages of manufacturing, as the wafers undergo one process, wait and proceed to the next process.

The cassettes are presented either manually or by conveyor. Once presented to the stocking system, sensors or a computer tell the robot, and the robot goes over and picks up the cassette and moves it to a commanded storage location inside the mini-cleanroom.

The cassette is carefully put into its storage location, then the robot awaits its next instruction from the host computer. This instruction could be to put another cassette away or to retrieve a cassette for delivery to the output area.

This is a very basic stocking application, but the applications can get very complicated very quickly. The need to handle multiple cassettes or different sizes of cassettes, the use of bar code readers and/or printers, the need for active calibration for larger stockers, and the incorporation of additional processes within the stocker system, as well as a wide variety of application-specific requirements, such as night-time kitting or inventory mapping, can quickly make the application a complex one.

From Sankyo's years of experience, they see the following as key requirements for these applications:

1. 1.

   (1) Capacity to handle a large number of units ­ usually measured in cassettes or trays, or some other product container. More than 500 cassettes and more than 5,000 trays are typical numbers encountered, though many systems have been much smaller.

   (2) Scaleability ­ different applications, different points in the process require different sized systems, either in length, height or in overall capacity.

   (3) Dexterity and smooth motion ­ to be able to reach into storage cells and carefully handle valuable products.

   (4) Basic repeatability ­ which must be inherent in the system's design. The target applications are again, storage and retrieval, not precision assembly, so the requirement here is more in the 0.25mm range.

   (5) Overall system speed ­ throughput is always important. How fast can you pick and store, or retrieve and deliver? Throughput is very application dependent.

   (6) Programmability ­ including the ability to handle different sensing schemes, communications with host systems, and the capacity to work with large databases. With programmability comes a truly flexible system.

   (7) Sensing ­ the system must support the use of sensors because the larger the system, the less precise it is going to be and this sometimes can require real-time calibration.

   (8) Reliability ­ because these systems must run 24 hours per day and human backup is difficult to provide.

   (9) The stocking robots have a long reach and heavier payload ­ environment is typically designed for automation, not for human intervention.

The CC-SCARA robotsNearly a decade ago, Sankyo Robotics developed a family of products to address this class of applications and meet the requirements for customers who manufacture wafers. The goal for these customers was to always have cassettes available to maximize the use of the expensive process equipment and to precisely and cleanly store and retrieve any specified cassette as required.

With similar requirements arising from a variety of wafer customers ­ and from disk manufacturers ­ a family of flexible, extendible products had to be developed which would use as much of the same design, parts, and processes as possible to minimize the non-recurring engineering and the resulting product cost to each customer.

Sankyo is one of the world's most knowledgeable and experienced manufacturers of SCARA-type robots and because they had a great deal of experience in Cartesian and track-based systems as well, the basic design of this family resulted in what is called the "CC-SCARA", a Cartesian-Coordinate SCARA-type robot system.

5-Axis CC-SCARA robot

ComponentsThe main components of the CC-SCARA are:

1. 1.

   (1) its scaleable track axis, typically measuring from 1-10m in length, though up to 16m is available. Typical track segments are 3m in length, so if increments of this length can be used, uniqueness can be minimized.

   (2) its tower-type Z-axis, measuring from 500mm in stroke to over 2m, with dust covers and, if necessary, with other fittings and features to allow it to operate in a class one environment.

   (3) a horizontally-articulated arm, which comes in a variety of configurations and sizes with either two or three degrees of freedom. For handling simple cassettes of 200mm wafers, this arm consists of a T1 and roll motor, with a gripper customized to the particular cassette in use. These arms are also class one capable.

   (4) a solid mechanical interface for attaching a gripper, pre-configured with internal cables and air supplies for end-of-arm interfacing.

Different mechanisms can be attached to the Z-tower in place of the arm ­ mechanisms such as precision X-Y tables with special sensing mechanisms or other measurement devices. As a result of Sankyo's experience in providing hundreds of these systems, they have developed a variety of grippers, some single acting, or servo-controlled, and some very complex in nature with multiple functions.

A variety of grippers is available

Gripper sensingAnother very important feature of the CC-SCARA systems is the sensing that can be designed into the end-of arm tools or grippers that are used and the related error detection and recovery procedures that can be implemented in the application programs. Typical sensing schemes for the handling of cassettes of wafers or disks include:

• •

  simple gripper open, gripper closed detection;

• •

  detection for the presence of a cassette in the storage cell;

• •

  detection for the presence of a cassette at input or output;

• •

  detection for the presence of a cassette in the gripper itself;

• •

  detection of a "jam" condition; i.e. the cassette is somehow jammed out of position.

A wafer handling robot

A wafer handling robot processes wafers simultaneously as the CC-SCARA robot handles cassettes

The related error recovery procedures, due to the value of the products being handled, typically include an audible notification to the system operator and the moving of the robot to a safe position. In some cases, the robot may be able to recover on its own, together with the host system, for conditions such as empty storage cell or empty input cell. However, any detected condition that could result in damage to the product really should require operator intervention once the robot system is safely secured. Certainly additional sensors and detection schemes can be added for other, more unique processes integrated into the stocker system.

Mini-stocker for wafer manufacturingOne example of a stocker system is a mini-stocker and processing system for one wafer manufacturing customer. In this system, the CC-SCARA becomes an integral part of a mini-cleanroom, all built around the robot. The overall system is a completely contained unit, which is one of the smaller stockers manufactured by Sankyo.

In this particular stocker there is an input/output area, service door, and an operator panel. Inside the stocker, there are storage shelves on both sides. On one side, there is also a small wafer handling robot which is processing individual wafers at the same time the CC-SCARA is handling the cassettes.

The combined result is a very tightly integrated and productive system.

Contact: David W. Heikkinen, Vice President, Sankyo Robotics, 1001-D Broken Sound Parkway NW, Boca Raton, FL, USA. Tel: (561) 998 9775; Fax (561) 998 9778; E-mail:Dave@Sankyo.com