Encoders are the preferred position feedback device. For some systems incremental encoders are a good choice. They can be very accurate but require a power on calibration of some sort, depending on the positioner configuration. Absolute encoders are just as accurate but do not require calibration on power up, but they come with a significant price increase. Our best offering (best value) is a AMO absolute encoder that give a absolute accuracy of +/- 4 arcsec (0.001 degrees or 20 uRad) at a 23-bit resolution. With that many bits of resolution, accuracy can be significantly increased by mapping out system level errors.

Yes, the host computer commanding the positioner can specify a velocity feedforward value in the commands to the positioner. This value is used to advance the position command and compensate for lag in the system.

Yes. This is limited to the available hardware layers and the bandwidth of the interface. But many of the common interfaces can be accommodated.

Yes, absolutely. The positioners are designed to accommodate a wide variety of payloads. There will be some limitation based on the physical dimensions of the payload and depending on how they are mounted to the positioner. Care must be taken to ensure that the payload will not impact any of the structure throughout the travel range of the positioner. It is highly desirable to balance the payload around all axes. An imbalance causes a torque due to gravity that is asymmetrical and can cause the system to be less stable at some orientations. Another limitation to consider it cabling. Most payloads require power and signal cables to and from the payload. Depending on the circumstances and customer preference, external or draped cables may suffice otherwise the accommodations for internal cabling must be specified as part of the positioner design requirements. Internal signal and power can be routed through an internal cable wrap but this limits the travel range of each axis to something less that +/-180 degrees. For system that require continuous travel a slip ring and/or rotary joint is used to pass signals across a rotary interface, thus allowing continuous rotation in any direction.

Depending on the contractual agreements, the position system can be delivered with the source code and tool chain in place. This allows for end user modification of the system software. However, this modification of the system software by the end user negates any warranty as this can be a risky activity causing damage to equipment and/or harm to personnel.

Depending on the contractual agreements, the position system can be delivered with the source code and tool chain in place. This allows for end user modification of the system software. However, this modification of the system software by the end user negates any warranty as this can be a risky activity causing damage to equipment and/or harm to personnel.

The bandwidth of the positioner system is dependent on several factors. Mostly the bandwidth is limited by the inertia and resonance of the customer payload. The larger the inertia and the lower the resonance the lower the bandwidth of the system. A typical mid-range system with 30 lbs of customer payload can have a position loop bandwidth from 2 to 10 Hz. However, this value can vary widely based on motor type and torque output, feedback sensor selection, bearing type, etc. Bandwidth is not an easy or direct comparison to a problem statement. Meaning what is important is not what the bandwidth is but rather, does the positioner track the target with the accuracy required. Bandwidth is related to accuracy but is not intuitive. I prefer to discuss the requirements in terms of the more direct comparisons such as step or ramp response or even statistical tracking errors. These are a better way specify the system characteristics in order to get the results desired.

Most system are either resolver based or encoder based. These are position sensors and for most system are sufficient. However, for more accurate system additional sensors can be utilized such as tachometers that provide higher quality velocity feedback. Additionally for situations where the positioner is in motion, it is typical to use inertial sensors (gyros, accelerometers, etc.) and/or external navigation instruments such as an Inertial Navigation Unit (INU) or an Inertial Measurement unit (IMU).

The motor selection is a critical aspect of the positioner design. The motor is selected based on the requirements of the system. Stepper motors are a good, low cost, solution for systems that can tolerate less performance from the motors. Stepper motors have discrete positions and are well suited for a geared system. Stepper motors are more difficult to control velocity and even with micro stepping can exhibit significant ripple in the motion. Brush or brushless motors tend to cost more but are higher performance motors. Brushless DC (BLDC) direct drive torque motors are the preferred solution. BLDC motors provide maximum torque at stall velocity and have smooth quiet operation. Brushless motors have no brushes to wear out and since the motor winding are on the stator (outside component) the heat transfer to the housing is better than with brush motors where the winding are on the rotor.