Posted by: Edmund Glueck | June 24, 2015

Electromagnetic Holding Brakes for Small Gearmotors and Motors

Holding, or “Power-Off,” brakes provide extra safety in applications where the load must remain in position in the event of power loss or equipment failure. Our design engineers have helped OEMs develop brake systems for hundreds of AC and DC applications, from home stairlifts to industrial applications. In this article, we focus on the principles of operation for the most common type of electromagnetic brake, the power-off design. For more information on clutches and braking techniques, see Chapter 10 in the Bodine Handbook.

Principles of Operation and Terms Bodine-Gearmotor-Brake-Post-1

The friction disc of a power-off brake is constrained and does not allow rotational motion when no voltage is applied to it. Another common term for this design is a “fail safe” brake.

The brake is designed with a wound coil that resides within a steel cup body. When voltage is applied, the armature plate is pulled toward the cup body by the magnetic force. The force is high enough to overcome the compression springs. When no voltage is applied, the compression springs exert a force on the armature plate to hold the friction disc firmly against the pressure plate, prohibiting rotation. The friction disc is coupled to the hub by a close fit geometric shape, usually hexagon or spline.

Brakes can be designed for any DC voltage. For AC voltage brakes, a bridge rectifier is used to convert AC voltage into DC. The bridge rectifier is either internal or external to the brake depending on the size of the brake.

Bodine-Gearmotor-Brake-Post-2   bodine-gearmotor-brake-post-3a
 

 

 


Dynamic vs. Static Braking

Depending on the type of application, either a static or dynamic brake may be required. The power-off brake design uses a friction disc material specific to static or dynamic braking applications. The more common version is the static brake design, where ideally the brake is engaged after the motor shaft has come to a stop. Static brakes are intended to hold static loads and the friction material experiences negligible wear over its life. Dynamic brakes are designed with a more durable friction material that wears over the life of the brake. When compared in a similar mechanical size package, dynamic brakes frequently will have a lower published torque rating than static brakes.

Brake Performance

Typical Holding Brake

Typical power-off holding brake

The brake has two states: power off and power on. During the transition to the power-off state, the magnetic field decays because of the removal of voltage to the brake. Here, the armature loses its magnetic couple with the wound coil, which clamps the friction disc to the pressure plate, applying the holding torque. The manufacturer can adjust the transition time, but is typically in the millisecond range. The performance of a 15in-lb. brake is shown in Figure 2. The sharp “spike” during the voltage decay is where the armature engages with the friction disc. Actual transition time is 60 milliseconds.

While charging the coil, there is a sharp “spike” when the armature   makes complete contact with the wound coil and releases the friction disc. Actual time for this event is 32 milliseconds.

Bodine-Gearmotor-Brake-Post-5Brakes are designed to operate continuously without overheating in the static holding position. Designs that include both dynamic and static braking require brakes with intermittent ratings. The duty cycle (braking and stop cycle) determines this rating.

 

 

 

Bodine-Gearmotor-Brake-Post-6

To download a PDF version of this blog post, please click here.

Copyright Bodine Electric Company © 06/2015. All rights reserved.

Bodine Gearmotor - Motor Constants - 12Motor constants are needed to calculate permanent magnet DC (PMDC) or brushless DC (BLDC or EC) motor specifications and ratings, or to match the motor properly to an amplifier. The motor constants are required in order to predict the PMDC or BLDC motor’s performance with changing variables, such as different input voltages or different loads. (See below PDF link for Bodine stock PMDC and BLDC motor constants.) This application note explains what the constants are, how they are derived and how to use them.

Common Motor Constants:

The most commonly used motor constants are Torque Constant (Kt), Voltage Constant (Ke), Electrical Time Constant (Te), Mechanical Time Constant (Tm), and Thermal Resistance (Rth). Typical values for these constants are derived by using measured values of No Load Speed, No Load Current, Stall Torque, Circuit Resistance, Circuit Inductance, and Armature Inertia with the following equations:

Torque Constant (Kt) — describes the proportional relationship between torque and current. Kt is usually expressed in the units Oz-in./Amp. See page 2 for additional information about torque constants.

Bodine Electric - Motor Constants - 03.26.2015

Voltage Constant, or Back EMF Constant (Ke) — is the Torque Constant expressed in different units, usually Volts/Krpm, in order to describe the proportional relationship between motor speed and generated output voltage when the motor is back driven as a generator in units of Volts/1000 rpm. See page 2 for additional information about voltage constants.

Bodine Electric - Motor Constants - 2

Electrical Time Constant (Te) — is the time required for a motor to reach 63.2% of its stall current after applying a test voltage with the motor shaft locked. It is usually expressed in milliseconds. Applied Voltage equals Rated Current multiplied by Circuit Resistance:

Bodine Electric - Motor Constants - 11

Mechanical Time Constant (Tm) — is the time required for an unloaded motor to reach 63.2% of its no load speed after applying its rated voltage. It is usually expressed in milliseconds.

bodine-gearmotor-motor-time-constants-5

Thermal Resistance (Rth) — is useful for predicting the ultimate temperature rise under different loading conditions in order to determine a maximum continuous torque rating. It is usually expressed in the units °C/Watt.

Bodine Electric - Motor Constants - 6

Using Performance Data to Calculate Kt and Ke

This speed/torque graph demonstrates how the linear equation of the current is used to calculate the Torque Constant (Kt) by using the slope “m.” The Voltage Constant (Ke) can then be calculated.

Using Performance Data to Calculate Kt and Ke

This speed/torque graph demonstrates how the linear equation of the current is used to calculate the Torque Constant (Kt) by using the slope “m.” The Voltage Constant (Ke) can then be calculated.

Bodine Electric - Motor Constants - 8

Bodine Electric - Motor Constants - 9

To download this information as a PDF, click here. To download the Motor Constants for Standard Bodine Gearmotors, click here.

To download Chapter 8, or any other section of the Bodine Small Motors Handbook, click here.

Copyright Bodine Electric Company © 04/2015. All rights reserved.

Posted by: Sarah Prais | April 10, 2015

Quiet Gearmotors for Medical Equipment

Bodine Electric_Mammography Machine - Medical EquipmentGearmotors in mammography equipment are used to raise and lower the scanner to accommodate the patient’s height. The primary design objective is smooth and quiet operation. Our team of design engineers addressed four aspects of the gearmotor design that contribute to quiet operation.

Worm Gearing
Bodine recommended a right-angle gearmotor with worm gearing. The sliding tooth action of worm gearing is generally quieter than the rolling action of spur and helical gearing. A second advantage for the application was that worm gears lock in place when there is no power to the gearmotor.

Machined Parts
By machining all mating surfaces of the motor and gearhousing, Bodine insured that the worm and helix gears, the motor armature and the motor end shield are precisely aligned. Better gear alignment translates into less noise. Unlike many gearmotors on the market today, all Bodine gearmotors feature machined surfaces throughout.

Ball Bearings Bodine Electric - Mammography Equipment - 2
Our engineers recommended ball bearings to minimize thrust loads on the driveshaft. Thrust loads can make the driveshaft shift back and forth within the gearbox. Ball bearings are pressed onto the driveshaft, locking it in place.

Quieter Brush and Commutator Components
Bodine engineers took several steps to reduce brush noise as much as possible. Special commutators were designed to prevent vibration and to ensure smooth brush contact. The brush holders were locked into the gearmotor endshield to prevent any “chatter”. Brush material and brush shape were optimized to minimize noise.

Bodine Electric engineers bring 110 years of application engineering and problem solving experience to a wide range of applications in industries as diverse as medical, packaging, industrial automation, and solar powered outdoors equipment. We look forward to working with you on your next FHP gearmotor design challenge.

Bodine Electric - Mammography Equipment - 3

Bodine Gearmotor Worm Gear Set PMDC Gearmotor

 

To learn more about Bodine Gearmotor Solutions in Medical Applications, click here.

Copyright Bodine Electric Company © 04/2015. All rights reserved.

Posted by: Edmund Glueck | March 18, 2015

Bodine Electric Gearmotors and Speed Controls

Bodine Gearmotors & Speed ControlsFrom our recent photo shoot: Bodine type 42R-GB/H, Hollow Shaft, AC 3-phase, Inverter Duty gearmotor, our type 24A4-P, 24VDC and 42A-FX, PMDC gearmotors. System matched to our selection of AC and PMDC motor speed controls – offered as chassis boards, NEMA-1 or NEMA-4. When a gearmotor and control are purchased as a set, enjoy our extended 2-year system warranty.

Posted by: Edmund Glueck | February 13, 2015

Bodine Gearmotors are Designed for Uptime!

Our team of MEs and EEs has the experience and knowhow to work on challenging applications across a wide range of industries. We are proudly celebrating 110 Years of “Quality in Motion” in 2015.

Our team of MEs and EEs have the experience and knowhow to work on challenging applications across a wide range of industries. We are proudly celebrating 110 Years of "Quality in Motion" in 2015.

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