Interior brake for servomotor builder
The project case history that follows shows the importance of supplier flexibility in product design, service, and delivery as more customers define their requirements in specific terms. Equally important, the story demonstrates the benefits of tapping a supplier’s expertise when you must design new products or solve application problems.
The challenge
Gettys Corp., an AEG company headquartered in Racine, Wis., makes precision motion control products including ac brushless servomotors and drives, and dc brush-type servomotors. The company’s products serve in material handling equipment, robotic systems, factory automation systems, and other applications. These applications require safe, rapid stopping or holding upon system shutdown or electric-power loss. A power-off friction brake on the servomotor can provide such operation.
When the motor builder repackaged and enhanced its S Series permanent magnet ac brushless servomotors to meet today’s automation market, it established stringent design and per formance crite ria for a spring-set, electrically released holding brake. With a totally enclosed, nonventilated (TENV) square frame design, the motors use high-energy rare earth magnets and they can withstand operating temperature to 180 C. The standard motors have Underwriters Laboratories (UL) recognition and Canadian Standards Association (CSA) approval. The related SX Series explosion- proof motors conform to UL specifications for motors serving in hazardous locations.
The power-off brake had to be customdesigned to operate inside the motor at high temperature and it had to meet UL Class H requirements. Also, the brake project required fast turnaround from initial design to delivery in order to meet the motor supplier’s production schedules. According to Curt Winter, director of engineering at Gettys, “The complexity of the brake, the critical performance criteria, the UL recognition, and the lower volume of such a specialized order seemed to dissuade most brake suppliers from taking the challenge.”
Making friends
Engineers at Deltran Div., American Precision Industries, accepted the challenge. They saw an opportunity that came with this project in the chance to participate in other projects. “We recognized the opportunity to establish a relationship with Gettys, which, as we anticipated, has led to other projects,” explains Maria Stopher, engineering manager at Deltran.
Choosing its team
The brake maker used its Design for Manufacturing & Assembly team to service the project. The DFMA team assembles the major disciplines within the company, including design engineers, quality control managers, machine- shop personnel, purchasing agents, and assembly- line employees.
From the beginning of the project, DFMA team members met regularly, each lending specific knowledge and experience to optimize the brake. Ongoing communication among team members assured project efficiency and cost-effectiveness. For example, knowing the design details ahead of time, machine-shop personnel were able to recommend a more efficient machining method. Quality control knew well in advance what gauges and equipment would be necessary for testing. And purchasing agents had more lead time to secure the tooling and materials.
The rules, made for any environment
Gettys defined its requirements, specifically: an electromagnetic, spring-set, friction brake, because the motor’s high operating temperatures could affect permanent- magnet brakes. Also, obtaining UL recognition meant the brake supplier had to upgrade the brake’s insulation system and components to meet Class H requirements, and drawings had to be submitted to UL for review.
A permanent-magnet brake that Gettys had used in the past required laborintensive disassembly to install it on the motor. Therefore, simplified design for ease of installation was another requirement. Furthermore, because the brakes would be enclosed inside sealed motors, which were often used in wet or hazardous environments, reliability was more important than ever.
Scoring
The brake supplier met all the performance criteria, and then some, with its spring-set, power-off Model BRP-50A brake, a new high torque-to-size-ratio design based on the company’s line of BRP friction brakes. The new brake has a 5-in. diameter and 2-in. axial length, with static torque rating of 360 lb-in. at 180 C. Its parallel-plate design has a low profile that meets the limited mounting depth inside the motor.
To meet UL Class H insulation system requirements and the potentially harsh environmental conditions, the brake engineers designed with UL-recognized materials including encapsulation compounds, 200-C Teflon lead wires, and plating for corrosion resistance. Also, because the SX Series motors must conform to UL specifications for motors in hazardous locations, the units must have no spark-producing component. Brake designers used a nonsparking aluminum rotor to meet this requirement.
The simplified design eases brake installation. The unit is reverse-mounted to better distribute overhung weight and the load shaft connects to the drive hub with a keyway and setscrews. A splined hub provides engagement and results in low backlash. “The brakes are so userfriendly, the people on our production line are asking for new frame sizes for other motors,” says Mr. Winter. “The brake’s air gap is factory-set so there’s no need to set it like we used to with the permanent- magnet style. That saves a lot of time and labor.”
Brake reliability is enhanced because of the low parts count. Parts include the coil installation, armature, friction rotor, springs, mounting flange, and hub. The brake manufacturer also performed life testing to ensure that the brake met or exceeded performance criteria.
Quick turnaround
Like many of the motor manufacturer’s products, the S Series is a specialized motor requiring timely introduction into target markets. Fast turnaround of the brake was essential for Gettys to meet production schedules. The combined skills of the DFMA team enabled the brake supplier to meet timing requirements. For example, machining methods recommended by machine-shop personnel helped speed production of brake components. And a suggestion by assembly employees to use ultrasonic welding technology reduced the number of parts to shorten assembly time.
Because of such teamwork, the brake was designed, developed, and delivered in 6 weeks, compared with normal cycles of 8 to 12 weeks by previous suppliers.
Winners all around
There were many additional gains for both brake supplier and motor maker. For example:
• The brake’s design allows for energy conservation because it draws less current than the brake that the motor maker had been using.
• The new brake is cost competitive.
• For the brake supplier, the project has led to other projects with the motor maker, and has resulted in the brake supplier being sole supplier for a number of other brakes. “We knew early on that if we provided the service, flexibility, and timing on this project, it could lead to even more,” says Bill Fierle, Deltran sales manager on the Gettys project.
John J. Mendolia is Director of Technical Services, Deltran Div., American Precision Industries, Buffalo. He has a mechanical engineering degree from the State University of New York at Buffalo, and has been designing electromagnetic brakes and clutches for more than 30 years — 29 of them with Deltran. Mr. Mendolia has created many innovative designs for aerospace, business-machine, and factory automation industries.