Stepper motors can be fitted to most Vacuum Generator manipulation equipment. Motors allow fast and remote operation and, when combined with our high performance drive-control units, these systems provide higher resolution than is possible with manual control.

Two standard controllers are available which allow a wide range of single axis or multi-axis control systems to be assembled. The controllers can operate either open-loop or encoded stepper motors.

• Motors are 4 phase, 8 lead hybrid stepper motors. They are supplied either as part of the manipulator or drive configuration, or as manual and motorised upgrades, and include the  appropriate mounting hardware and microswitches.
• Motors are normally supplied with flying leads. If required, the motor (and limit switches if appropriate) can be supplied wired into the mating connector, suitable for all VG Scienta controllers. To select this option add 'W' to the motor kit Order Code, e.g. MRXMOTZW.
• All motors can be fitted with an incremental encoder for closed-loop. To select this option add 'E' to the kit Order Code, e.g. MRXMOTZE. This code, which includes wiring to the 'W' standard above, is supplied with connectors and wiring suitable for all controllers.

• All motors and controllers are compatible and interchangeable.
• All controllers include a power supply, mains cable, RS232 Cable, and jog link cable, where appropriate. Any necessary connectors for additional I/O functions are also supplied. We refer to the packaged unit as a 'controller' for simplicity.
• The controllers are housed in screened enclosures that resist electromagnetic radiation and conform with the latest European Safety Directives.
• Three control levels are available: simple push button control, programmable open-loop and programmable closed-loop control.
• All controllers use the same high power drive so that the motor torque-speed performance is the same with any controller.
• Programmable controllers use a simple control language that can be entered through the RS232 interface. Program sequences can be downloaded and stored in the controller for repetitive control operations.

• Phase switching. This determines the sequence in which the four motor phases are energised. Our controllers use 'Bipolar chopped' phase switching., which utilises all phases at the same time for maximum efficiency.
• Rail Voltage. This reference voltage determines the shape of the pulse sent to the motor. In general, the higher the rail voltage, the more energy will be transmitted to the motor. We use a 36V rail, which can give the motor significantly more torque than a 12 or 24V rail supply.

Step Sequencing

Stepper motors are constructed with 200 steps per revolution (1.8° per step). Motor drives are produced for full step, half step or microstepping modes. VG Scienta controllers all use half step sequencing (0.9° per half step).

• Full Step mode. This is a common sequencing method as it is simple and provides good torque and repeatability. The drive delivers 200 electrical pulses to give 200 mechanical steps per revolution. Resonance and vibration can be a problem in full step mode.
• Half Step mode. The drive can arranged so that the magnetic poles of the motor are energised in either direction allowing the motor to be driven in smaller increments of 0.9° per step. This is much smoother than full step mode and angular resolution is improved by a factor of two.
• Microstepping. This is a more complex sequencing arrangement in which the motor is 'balanced' between steps to give (typically) 1400 microsteps per revolution. This gives very smooth operation, but positional accuracy is affected by load. The repeatability of microstep drives is not good as half step or full step drives.

Open and Closed Loop Control

Open loop controllers supply a number of electrical pulses to the motor corresponding to the number of steps required. They rely on good torque-speed performance to avoid motor stall which will not be detected by the controller. Closed loop controllers check the angular position of the motor at the end of the move, or the position of the device being moved. Any errors between the demanded and the actual position will be corrected if possible. This position check requires an encoder to be fitted to the motor or driven component. VG Scienta stepper controllers all have encoder input channels and can therefore operate under open or closed loop control.