Housed-DDR systems are best suited to applications where the load rides 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. In such cases, they offer fast and easy installation, a prealigned feedback device, built-in bearings, and significantly lower cost than a frameless design.

CARTRIDGE SYSTEMS
Cartridge DDR systems represent a new approach to directdrive rotary motors. They provide all the benefits of housed designs in a unique bearingless housing, permitting use on machinery that already has bearings. A compression coupling connects the rotor to the shaft, and a shipping clamp facilitates mounting so a unit can be up and running in less than 30 min.

Cartridge DDR motors can be used in converting, factory automation, packaging, printing, and semiconductor industries. The cartridge technology adapts 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 benefits that include:

• Zero maintenance
• Zero backlash
• Improved repeatability
• Zero compliance
• Improved accuracy
• More compact mechanical design
• Quiet operation
• Improved velocity regulation
  
  

Many DDR designs are also available in hollow-shaft configurations that permit electrical and pneumatic lines or other machine components to pass through the motor and optimize space.

However, different electromagnetic designs will have different performance levels, cost points (cost for the torque available), and top-speed capabilities.

For instance, variable-reluctance motors do not offer the performance, torque, or speed available from brushless, high-energy permanent-magnetic motors. Also, variable-reluctance systems often must specifically match the drive amplifier to the motor. This limits flexibility in drive selection and makes servicing more difficult.

Some machines can benefit from the use of different DDR designs on different machine axes. Ideally, a single manufacturer that can provide the motors and a common drive amplifier to run them all. This common platform eliminates the need to learn and support multiple designs.

Direct-drive systems have higher initial costs than conventional servosystems. This can vary from as little as 30% more for cartridge systems to as much as four times more for frameless systems (total cost including design and integration). This cost picture changes quickly when life-cycle costs are examined. Over a typical five-year life, conventional systems will cost from three to 10 times more than direct-drive systems due to maintenance and downtime.

The benefits of direct-drive systems 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 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 zeromaintenance operation.