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Republished with Permission from MetalForming magazine - copyright 1997.

"Tool Changers Enhance Robot Versatility"

Robotic tool changers provide robots with the flexibility to change end effectors and other peripheral tooling automatically. They are designed to function for millions of cycles at rated loads, while helping to maintain extremely high repeatability. For example, automakers maintain just-in-time production scheduling of automobile body parts, while tool changers switch press blank sizes, as many as four or five times per shift.  

Enabling a single robot to exchange end effectors during a manufacturing or assembly process much as a human is capable of operating different tools increases robot flexibility. In a multitude of automatic tool changing applications, the bottom line is a significant reduction in expensive, non-productive tool changing time.

Anatomy of Quick-Change

A programmable robot capable of a variety of tasks requires a quick means to change the end- effector. Because it is essentially an extension of the robot arm, an automatic tool changer must possess physical characteristics that are at least equivalent to the robot arm itself. It must hold the tool securely - even if electrical power or the air supply fails.  

Examples of high precision robotic tool changers are ATI Industrial Automation's patented Quick-Change tool changers. The changer has a master plate mounted on the robot arm and a tool plate attached to the tool. The heart of the locking mechanism is an air-actuated piston on the master plate. The nose of the piston has a 45 deg. taper. Next is a cylindrical section, and finally, a 15 deg. taper.

Tool Changer--Marketing Accessory

FANUC Robotics North America, Inc., produces a variety of industrial robots and robotic systems. Applications for machines and systems developed by FANUC cover the manufacturing waterfront, including welding, painting and dispensing, palletizing, parts handling, press loading/unloading, etc.  

Within its Auburn Hills, MI, headquarters, FANUC Robotics maintains a complete demonstration and instructional facility. Because of the wide range of potential applications, the demo room needs a quick means of switching from one tool to another.

"The Quick-Change tool changer really helps us to demonstrate the versatility of our robots," says Robert Anderson, product/application engineer. "Design of the Quick-Change makes for easy programming of tool pickups. The 45-deg. taper on the piston serves to pilot the two plates together--positioning does not have to be precise."

Anderson says he particularly likes the fail-safe feature. "Sometimes, in a training session, we will turn off the locking air pressure during the discussion period. It is reassuring to know that the tool can't fall off." The only way to remove the tool is to pressurize the unlatching mechanisms.

Getting a Grip on Assembly

Automakers were robotic system pioneers, staffing their press loading lines with robots. Now, more affordable systems and technological advancement in automated tool changers, manipulators, controls and safety equipment make robots attractive to smaller manufacturers.  

By using robots in tandem, or in single-loading systems, producers of all types of assembled products are garnering the benefits of:

  • Increased production rates--robots generally load and unload faster, as well as eliminate operator fatigue and downtime between shifts;  
  • Reduced personnel injury--operators are out of harms way as the robot performs in even the most severe environment;   
  • Added flexibility--robots can be programmed to perform continuous or intermittent cycles and handle a wide variety of shapes and sizes of components; and 
  • Fast return on investment--the payoff being labor savings, productivity increases, reduced in-process inventory and reduced parts damage.

Growth in Pressing and Stamping

More than 50 percent of robotic applications in the automotive industry perform welding operations. In the second largest applications arena--pressing and stamping--material handling robots bring sheet blanks to the presses and remove shaped hoods, decks, fenders, bumpers and a wide variety of under-body components.  

In press-to-press operations, each application needs a different arrangement for gripping the part. Most grippers are pneumatic suction cups. Some are mechanical grippers. With just-in-time manufacturing, the press line may change as many as four or five times each shift. Obviously, the tool changer becomes a crucial part of the system.

Japanese car makers were the first to capitalize on the safety, flexibility and maintenance benefits available using both automatic and manual changers in press-to-press stamping applications. In the early 1990s, Nissan and Mazda led the way, making significant investments to make the stamping operation flexible, while moving personnel away from the relatively hazardous pressing operations. Other Japanese producers soon followed suit, including companies whose products target the construction and agricultural industries.

Soon after, General Motors, Australia, began installing programmable robots in pressing and stamping operations. Now, most U.S. stamping plants are changing to, or at least considering, the use of flexible tooling.

In addition to safety benefits, robots provide the flexibility to switch production in minutes. Before, the switching chore used dedicated tooling, which robbed precious production time; that is, if the tooling could be changed at all. Today, a stamping press can go from producing a light truck fender, to a muscle-car bumper and be up and running in just minutes.

Maintenance benefits are obvious. When a tool wears, the ability to remove it and replace it in seconds using automatic tool changers, keeps the stamping production line up and running.

The capital investment needed for automatic tool changing on stamping and pressing lines is considerable. However, a companion trend toward automatic die changing may help to accelerate the decision-making process for U.S. manufacturers. The combination of automatic material handling, tool changing and production die changing, promises enormous production benefits.

Robotic Implementation

If a robotic system seems feasible for a company's manufacturing and assembly process, how the company chooses to buy and implement the system remains one of its important decisions. In many cases, buying the robot, gripper and control station may be all that is requiredÑif the company is capable of installing the programmable logic controller, safety equipment and other peripheral hardware.  

A wide variety of tool changers are on the market. The selection process is crucial because tool changers may add three to 10 percent to the cost of a system. Value received must include versatility and flexibility, which affects a robot's repeatability, payload, movement capacity and operational life.

Whatever decision is made, the end result should be a comprehensive robot package of electrical, mechanical and control components designed to work together. The ultimate choice will improve the competitiveness of the manufacturer. MF

How to Select a Robotic Tool Changer

Take care to examine tool-changer specifications since tool-changer manufacturers vary the margin-of-safety factor.
Calculated Method:

The strength of robotic tool changers is based upon their moment capacity. Use the following method to approximate your worst case scenario.

  • Find the approximate center of gravity (CG) of your heaviest end effector.
  • Calculate the distance (D) from the CG to the bottom of the tool plate.
  • Calculate the weight (W) of the heaviest end effector.
  • Multiply (W) times (D) to get an approximate static moment (M) or a moment based upon one G of inertia.
  • Find Quick-Changer (QC) with a static moment capacity of equal or greater value than (M).

Robots may produce moments that are two to five times higher than their static moment due to potential high acceleration. Check the QC specification for static and dynamic moment capacity.

Pneumatic and Electrical:
Determine the number and size of pneumatic and electrical contacts needed. Larger Quick-Changers have larger and more numerous pneumatic ports and electrical contacts.
Temperature and Chemicals:
Most QCs use nitrile o-rings. Nitrile can handle temperature ranges from -20 deg. F to +150 deg. F, and can withstand most chemicals. If temperatures are outside this range, or you are not sure of resistance to chemicals, you should contact the QC manufacturer.
Precision Applications:
When dealing with applications that require high repeatability, check the manufacturer's repeatability specifications. Also, ask if repeatability has been tested to one million cycles.  

Keep in mind that a tool changer affects your robot's moment capacity, payload, wear, size and repeatability. Select a Quick-Changer with a capacity that exceeds that of your robot.




   
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