Motion Control Drives
Drives are amplifying devices used to control the motor based on feedback it receives. There are two groups of drives – Analogue and Digital.
Analogue Drives
Analogue Drives are subdivided into three predominant categories – Velocity, Torque and Power Block.
Systems that use any of the three types of analogue drives can be surmised into the basic components shown in the block diagram below. The difference in the analogue drive types are determined by which functions take place in the controller and which in the drive. These different types are illustrated on our Analogue Drives page. The motor is obviously the end function of the system and the encoder is used to provide feedback to various stages in the system.
Digitial Drives
Digital Drives come in two different types – Non-Regenerative and Regenerative an explanation of each can be found on our Digital Drives page. Digital drives convert incoming AC to DC during which it can regulate speed, torque, voltage and current conditions of the DC motor. It controls the power to the motor by altering the triggering rate of the conversion from the AC supply. By triggering at the beginning of the cycle 100% power is converted, by triggering later, less power is converted as illustrated below.
Comparison of Analogue and Digital Drives
Analogue Drive Advantages |
Digital Drive Advantages |
Use conventional, low cost, 3-phase AC induction motors for most applications. |
Less complicated due to single-power conversion (AC to DC only). |
AC motors require very little maintenance and are preferred for applications where the motor is mounted in an area not easily reached for servicing or replacement. |
Often less expensive for most horsepower ratings. |
AC motors are smaller, lighter, more commonly available, and less expensive than DC motors. |
DC motors have traditionally been adjustable-speed machines and a wide range of options have evolved for this purpose |
AC motors work better in high-speed operation since there are no brushes or commutators. |
Cooling blowers and inlet air flanges provide cooling air for a wide speed range at constant torque. |
Wet, corrosive or explosive operating environments require special motor enclosures. Special AC motor enclosure types are more common and cost less. |
Availability of accessory-mounting flanges and kits for mounting feedback tachometers and encoders. |
Multiple motors in a system can operate simultaneously at a common frequency/speed. |
Digital regenerative drives are available for applications requiring continuous regeneration for overhauling loads. AC drives with this capability would be more complex and expensive. |
It is advantageous to use an existing constant-speed AC motor already mounted and wired on a machine. |
If done properly, brush and commutator maintenance is minimal. |
Lack of commutators and brushes are important when the application load varies greatly and light loads are encountered for prolonged periods. DC motor commutators and brushes can wear rapidly under this condition. |
DC motors can provide starting and accelerating torques in excess of 400% of rated. |
Low-cost electronic motor reversing. |
Some analogue drives may be noisy which is undesirable in some applications. |
A back up (constant speed) is available if the controller fails. |
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