When Remotec was searching for the best brake for its application, Ogura engineering responded with a series of questions that helped fine-tune a brake for the specific application. These questions are:
- For what purpose will the brake be used? A brake is used for two reasons: to stop or to hold a rotating load. While this may seem to be a very elementary concept, it is critical to specify the intended use when choosing the correct model. Minor design and component differences such as friction disc material and spring force are considered when determining the correct brake for the application. A brake can be specifically designed to dynamically stop a load, to simply hold a load in place, or to do both. The wrong choice can mean premature brake failure or worse, a catastrophic system failure -- envision an elevator with a misapplied brake.
- How often will the brake be used, and what is its expected life? Factors such as life expectancy and heat buildup in a high cycle-rate application will determine the appropriate friction material.
- In what type of environment will the brake operate? Relative humidity, exposure to the elements, use in food machinery, and other environmental aspects all have an impact on how the brake will function.
- What are the envelope dimensions and size constraints? These parameters will determine the size and shape of the brake.
- Is a manual release required? In some cases it is necessary to release the brake in an emergency situation. An example is a powered wheelchair that loses its battery charge. In this instance the operator would necessarily have to release the brake to allow the wheels to rotate.
Size is critical for Remotec’s application and it wanted to have a very thin profile brake. Based on Remotec’s requirements, Ogura's RNB series was chosen. This series is primarily designed for holding, but can accommodate emergency stops. Each rotating portion of the robot uses an Ogura brake. There is one brake used in the shoulder, elbow, and wrist of the robot. The brake is attached to the back end of a servo motor/gearbox, which controls the movement of each section.
The Ogura RNB brake is primarily used for holding a load in place. When the servomotor is running, the brake field is energized, so a magnetic field is generated, attracting the steel pressure plate. When the pressure plate is pulled toward the field, it compresses six small coil springs. This releases pressure against the friction disc in the brake. The hub on that disc is connected to the motor shaft, so as long as power is applied to the brake, the motor can spin freely in either direction.
When the motor is no longer required to turn and reaches zero rpm, voltage is no longer applied to the field, so the six coil springs push on the pressure plate, which, in turn, pushes on the friction disc that is attached to the hub on the motor shaft holding the motor/reducer in place.
If the robot was handling a heavy load and there were no brakes, the load may have the ability to back-drive the system, causing the load to fall. Obviously, this could be very dangerous, especially if the robot was handling explosives.
The Andros robot is capable of being controlled remotely in a number of ways depending on the method of communication and distance from the target subject. Via a hard tethered cable, it is capable of communication from a distance of 100 meters; with fiber optics over 365 meters; and through a digital radio signal it has a range of up to 1,000 meters. Integrated sensors in the arm joints, articulators, and gripper (HD SXT only) provide instant on-screen position feedback. Since there are so many variables and/or obstacles involved in a mission, the Andros can run for an extended time. It is capable of over four hours of operation.
— Michael Vasko is regional sales manager for Ogura.