Saturday, October 14, 2006
Direct drive motors offer attractive servo choice
Direct drive motors are becoming more common because they offer a number of advantages over conventional rotary servomotors. The absence of a gearbox means that the resulting servo system is much quieter, and also requires less maintenance than existing configurations. Most servo systems use a conventional rotary servomotor that is coupled to the driven load through a gearbox or belt drive.
Although conventional servo systems in and of themselves are maintenance-free, performance issues such as position inaccuracy or difficult tuning problems can be introduced by the backlash or compliance from the gearbox or belt drive.
In fact, even systems that do not employ gearboxes or belt drives can have excessive compliance issues from the couplings used to connect the servomotor to the load.
These coupling methods will take a maintenance-free servomotor and introduce new maintenance requirements, such as gearbox lubrication and belt adjustment/replacement.
Gearheads are typically required to improve the torque and improve the inertial match of the servomotor to the load, but new technological developments make direct motors drives a viable alternative.
Direct drive rotary (DDR) systems provide the benefits of a brushless servomotor solution, while eliminating the drawbacks created by couplings, gearbox backlash and gearbox/belt maintenance.
By coupling the motor directly to the load, all mechanical transmission components are eliminated.
In addition to solving the maintenance headaches, DDR systems do not require inertia matching, position and velocity accuracies can be increased up to 50 times, and audible noise is reduced by up to 20dB.
For designers who need to reduce machine size, the elimination of the mechanical transmission components results in a smaller machine that boasts higher performance, quieter operation and zero maintenance of the motion control system.
Frameless DDR systems comprise a separate rotor and stator without bearings.
These components are designed into the machine and become an integral part of the machine.
The feedback device (such as a resolver, encoder, hall sensors etc) must also be designed into the machine.
Frameless DDR systems were Danaher Motion's original DDR technology.
Most frameless DDR motors are custom designs, which make them good candidates for applications where space is limited or weight is critical.
There are standard catalogue versions of frameless DDR motors available.
These are less common but offer the benefits of ready availability, UL approved design and pre-engineered feedback designs.
Frameless DDR motors are ideal for aerospace/defence applications such as aircraft or ground vehicle radar and weapons systems.
They also make sense in high performance industrial applications, robotics and precision grinding being good examples.
When the lowest size and weight must also deliver optimum performance, frameless DDR systems are an excellent solution.
Housed DDR systems, also referred to as 'full frame' systems, integrate the rotor, stator, and factory aligned feedback within a housing that includes precision bearings.
Although such systems still require the selection of a compatible drive amplifier, they represent a standard solution that is much easier to select, integrate and service than a frameless solution.
Housed DDR systems are best suited to applications where the load is designed to ride on the motor's bearings.
Where a machine already has bearings the motor must be coupled to the load or multiple sets of bearings must be aligned, a complex and time-consuming task.
Housed DDR motors are generally used in applications without existing machine bearings, such as indexing and rate tables.
For applications suited to the housed DDR design, they offer fast and easy installation, a pre-aligned feedback device, built-in bearings, and significantly lower cost than a frameless design.
Cartridge DDR motors represent a completely new category of direct drive technology that combines all the performance benefits of frameless DDR motors with the ease of installation of a full frame motor, and at a significantly reduced price point than conventional DDR technology.
Their unique 'bearing-less' design facilitates mount-and-run operation in less than 30 minutes.
Cartridge DDR motors can be used in a wide variety of applications in the converting, factory automation, packaging, printing, and semiconductor industries.
The cartridge technology can be adapted to nearly any application that has existing bearings, providing all of the benefits of direct drive at the lowest cost, and with fast, easy installation.
All DDR systems provide a common set of benefits that include zero maintenance, reduced downtime, zero backlash, improved repeatability, zero compliance, improved accuracy, more compact mechanical design, quiet operation, and improved velocity regulation.
Many DDR designs are also available in 'hollow shaft' configurations that permit electrical lines, pneumatic lines or other machine components to pass through the motor for optimised space utilisation.
Not all direct drive systems are available from all manufacturers.
Moreover, different electromagnetic designs will result in different levels of performance, different cost points (cost per torque available), and different top speed capabilities.
Variable reluctance motor designs do not offer the performance, torque or speed capabilities available from brushless, high-energy permanent magnetic motors.
Also, variable reluctance motors often require that the drive amplifier be specifically matched to the motor.
This limits flexibility in drive selection and makes service more difficult.
Some machines can benefit from the use of different DDR designs on different machine axes.
Ideally the motors should come from a single manufacturer that can provide a common drive amplifier design to run all the different motors.
This provides a common platform and eliminates the need to learn and support multiple designs.
Direct drive systems will have higher initial costs than conventional servo systems.
The degree of difference can vary from as little 30% more for a cartridge system, to as much as four times more for a frameless system (total cost including design and integration).
This cost picture changes quickly when the lifecycle costs are examined.
Over a typical five-year life the conventional system will cost from three to ten times the direct drive system costs due to maintenance and downtime.
On a final note, the benefits of direct drive technology are not limited to just rotary motion applications.
Direct drive linear (DDL) systems eliminate mechanical translation devices such as ball/lead screws or rack and pinions, offering the equivalent performance and maintenance-free operation improvements to linear systems that DDR systems offer to rotary systems.
Machines that combine DDR and DDL systems provide the ultimate in performance and zero maintenance operation.
Although conventional servo systems in and of themselves are maintenance-free, performance issues such as position inaccuracy or difficult tuning problems can be introduced by the backlash or compliance from the gearbox or belt drive.
In fact, even systems that do not employ gearboxes or belt drives can have excessive compliance issues from the couplings used to connect the servomotor to the load.
These coupling methods will take a maintenance-free servomotor and introduce new maintenance requirements, such as gearbox lubrication and belt adjustment/replacement.
Gearheads are typically required to improve the torque and improve the inertial match of the servomotor to the load, but new technological developments make direct motors drives a viable alternative.
Direct drive rotary (DDR) systems provide the benefits of a brushless servomotor solution, while eliminating the drawbacks created by couplings, gearbox backlash and gearbox/belt maintenance.
By coupling the motor directly to the load, all mechanical transmission components are eliminated.
In addition to solving the maintenance headaches, DDR systems do not require inertia matching, position and velocity accuracies can be increased up to 50 times, and audible noise is reduced by up to 20dB.
For designers who need to reduce machine size, the elimination of the mechanical transmission components results in a smaller machine that boasts higher performance, quieter operation and zero maintenance of the motion control system.
Frameless DDR systems comprise a separate rotor and stator without bearings.
These components are designed into the machine and become an integral part of the machine.
The feedback device (such as a resolver, encoder, hall sensors etc) must also be designed into the machine.
Frameless DDR systems were Danaher Motion's original DDR technology.
Most frameless DDR motors are custom designs, which make them good candidates for applications where space is limited or weight is critical.
There are standard catalogue versions of frameless DDR motors available.
These are less common but offer the benefits of ready availability, UL approved design and pre-engineered feedback designs.
Frameless DDR motors are ideal for aerospace/defence applications such as aircraft or ground vehicle radar and weapons systems.
They also make sense in high performance industrial applications, robotics and precision grinding being good examples.
When the lowest size and weight must also deliver optimum performance, frameless DDR systems are an excellent solution.
Housed DDR systems, also referred to as 'full frame' systems, integrate the rotor, stator, and factory aligned feedback within a housing that includes precision bearings.
Although such systems still require the selection of a compatible drive amplifier, they represent a standard solution that is much easier to select, integrate and service than a frameless solution.
Housed DDR systems are best suited to applications where the load is designed to ride on the motor's bearings.
Where a machine already has bearings the motor must be coupled to the load or multiple sets of bearings must be aligned, a complex and time-consuming task.
Housed DDR motors are generally used in applications without existing machine bearings, such as indexing and rate tables.
For applications suited to the housed DDR design, they offer fast and easy installation, a pre-aligned feedback device, built-in bearings, and significantly lower cost than a frameless design.
Cartridge DDR motors represent a completely new category of direct drive technology that combines all the performance benefits of frameless DDR motors with the ease of installation of a full frame motor, and at a significantly reduced price point than conventional DDR technology.
Their unique 'bearing-less' design facilitates mount-and-run operation in less than 30 minutes.
Cartridge DDR motors can be used in a wide variety of applications in the converting, factory automation, packaging, printing, and semiconductor industries.
The cartridge technology can be adapted to nearly any application that has existing bearings, providing all of the benefits of direct drive at the lowest cost, and with fast, easy installation.
All DDR systems provide a common set of benefits that include zero maintenance, reduced downtime, zero backlash, improved repeatability, zero compliance, improved accuracy, more compact mechanical design, quiet operation, and improved velocity regulation.
Many DDR designs are also available in 'hollow shaft' configurations that permit electrical lines, pneumatic lines or other machine components to pass through the motor for optimised space utilisation.
Not all direct drive systems are available from all manufacturers.
Moreover, different electromagnetic designs will result in different levels of performance, different cost points (cost per torque available), and different top speed capabilities.
Variable reluctance motor designs do not offer the performance, torque or speed capabilities available from brushless, high-energy permanent magnetic motors.
Also, variable reluctance motors often require that the drive amplifier be specifically matched to the motor.
This limits flexibility in drive selection and makes service more difficult.
Some machines can benefit from the use of different DDR designs on different machine axes.
Ideally the motors should come from a single manufacturer that can provide a common drive amplifier design to run all the different motors.
This provides a common platform and eliminates the need to learn and support multiple designs.
Direct drive systems will have higher initial costs than conventional servo systems.
The degree of difference can vary from as little 30% more for a cartridge system, to as much as four times more for a frameless system (total cost including design and integration).
This cost picture changes quickly when the lifecycle costs are examined.
Over a typical five-year life the conventional system will cost from three to ten times the direct drive system costs due to maintenance and downtime.
On a final note, the benefits of direct drive technology are not limited to just rotary motion applications.
Direct drive linear (DDL) systems eliminate mechanical translation devices such as ball/lead screws or rack and pinions, offering the equivalent performance and maintenance-free operation improvements to linear systems that DDR systems offer to rotary systems.
Machines that combine DDR and DDL systems provide the ultimate in performance and zero maintenance operation.
# posted by Medical Information : 2:36 AM
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