Novel brush design boosts DC motor reliability

A PennEngineering Motion Technologies - Europe product story

Edited by the Engineeringtalk editorial team Feb 10, 2005

PennEngineering Pittman brand, brush commutated DC motors are very much in demand for motion and positioning applications.

PennEngineering Pittman brand, brush commutated DC motors are very much in demand for motion and positioning applications.

Brushed DC motors and gearmotors offer smooth and precise performance with moderate cost when compared with brushless motors and their associated control electronics are cost-effective and straightforward.

Improvements in brush DC motor design is a continual challenge for Pittman, enabling it to meet today's high performance applications with products that provide long life and high reliability with competitive costs.

As the primary cause of failure in brush commutated DC motors is the combination of ongoing brush wear and performance problems caused by a reduction in spring pressure associated with traditional brush designs, Pittman has sought to slow the wearing process by targeting brush design, brush size and brush materials.

As a solution, Pittman has developed its "SuperBrush" cartridge brush assembly - a specially designed cartridge mechanism with torsion spring assemblies to ensure constant brush force over the life of a motor.

The cartridge brush assembly fits into the motor base and consists of a two-piece, high temperature plastic, snap-together assembly in which each of two brushes is seated securely within its own individual slot.

The cartridge design permits the brushes to travel with a linear motion and the design further provides the ideal brush pressure to withstand the detrimental effects of mechanical wear.

The "SuperBrush" design contains 60% more brush material and offer the potential for longer motor life compared with smaller and faster-wearing, conventional brushes.

So successful has been the concept that "SuperBrushes" are now included in the majority of standard Pittman brand, brushed DC motors and gearmotors.

Alternative high-performance brush materials can also be specified as another means to help prolong effective brush life.

Electrographitic is one among many relatively new and durable brush materials now offered by the company in addition to standard copper graphite brushes to curb problems associated with brush wear.

Other developments aimed at maximising performance and extending motor life include the integration of advanced materials.

Thinner bonded neodymium magnets can provide advantages both in terms of design and performance.

Two-pole permanent magnet stators in brush DC motors are generally constructed of ceramic magnets, which are enclosed in heavy-gauge steel return rings.

The new thinner bonded neodymium magnets are more powerful but take up less space than conventional ceramic-only types.

Smaller, thinner magnet materials allow for larger motor armatures to be designed into smaller motor frames, which in turn can produce more continuous torque and, consequently, more power.

A challenge for Pittman motor designers working with smaller motor lines is how and where to integrate connectors, tabs and wires, capacitors for RFI suppression, brush assemblies and other components, whether standard or custom.

One solution has been to develop internal PC boards for surface-mount components which can serve as platforms to incorporate components without affecting motor size and weight.

They can be engineered in a circular shape for mounting easily inside a motor's frame or configured for mounting in an encoder housing.

Pittman produces many customised and modified motor designs to include these advanced features have developed a great reputation for innovative "assembly-line-ready" product design where the user requires little or no additional wiring and further benefits from the integration of special shafts, adapter plates and other interfacing components included with the motor or gearmotor.