Motion Resolution Value Examples

Motion Resolution is one of the Motion Scaling attributes. These examples demonstrate how the Motion Resolution value may be used together with the Conversion Constant to handle various machine applications.

Direct-Drive Rotary Shear Application

In this mechanical configuration a rotary motor is directly driving a rotary shear drum equipped with three knives to cut a product to specified length, thus producing three products per revolution of the output shaft. Because the default Motion Resolution value is 1,000,000 Motion Counts/Motor Rev and the user's Position Unit is, say, Products, the Conversion Constant would be 1,000,000/3 Motion Counts/Product. This is particularly problematic when configured to perform an Unwind operation every product cut cycle where a 1/3 count error would accumulate with every cycle. But, because Motion Resolution is configurable, you can simply set the Motion Resolution to 300,000 Motion Counts/Motor Rev and the Conversion Constant could then be set to 100,000 Motion Counts/Motor Rev, and a Rotary Unwind value of 100,000 Motion Counts/Cycle.

Because the Conversion Constant is now a clean rational number, this system scales without any loss of mechanical precision, for example, a move of three Products would move the output shaft exactly one revolution. By setting the Travel Mode to Cyclic, entering Position Scaling of three Products per Motor Rev, and a Position Unwind value of one Product per Cycle, appropriate values for scaling factors, Motion Resolution, Conversion Constant, and Rotary Unwind are automatically calculated.

The control system is responsible for scaling Motion Counts into equivalent Motor Feedback Counts. In this case, because the motor is directly coupled to the load, one rotation of the shearing drum translates to one revolution of the motor feedback device. Assuming that the motor feedback device is a typical optical encoder with 4000 Feedback Counts/rev, a displacement of 300,000 Motion Counts would be scaled by the control system to be 4000 Feedback Counts.

Rotary Shear Application with Gearbox

Instead of the motor directly driving the rotary shear drum, in this application example the motor is driving the shearing drum through a 3:1 gearbox. Since the Motion Unit is tied to the load, for example, Load Rev, the Motion Resolution, Conversion Constant, and Rotary Unwind determined in the example above apply equally well to this application.

The scaling of Motion Counts to Motor Feedback Counts, however, is not the same due to the presence of the gearbox. In this case, one revolution of the shearing mechanism translates to three revolutions of the motor. Nevertheless, the control system has a count scaling feature that performs this scaling automatically. This is done by selecting a Rotary Transmission as the Load Type, and setting the Transmission Ratio Output to 1, and the Transmission Ratio Input to 3. In this way, 300,000 Motion Counts per Load Rev is scaled exactly to 12,000 Motor Feedback Counts, or three Motor Revs.

Rotary Motor with Gearbox/Ball-Screw Application

Because this is a linear application, Motion Resolution would be expressed as Motion Counts per Load millimeter m or Load inch, in this case, say millimeter.

The motor feedback would, however, be rotary and resolution expressed in Motor Feedback Counts per Motor Rev, in our case 4000 Feedback Counts per Motor Rev. The default Motion Resolution is 1,000,000 Motion Counts per millimeter and if the Position Unit is, say, centimeters, the Conversion Constant would be 10,000,000 Motion Counts per centimeter. This would be automatically calculated by entering a Position Scaling of 1 centimeter per 10 millimeters.

Given that our application uses a 4:1 gearbox and a 5 mm pitch ball-screw, 5 mm of ball-screw travel translates to 4 revolutions of the motor, or 16,000 Feedback Counts. Again, the control system's count-scaling feature performs this scaling automatically. This is done by selecting Linear Actuator as the Load Type, setting the Transmission Ratio Output to 1, and the Transmission Ratio Input to 4, setting the Actuator Type to be "Screw", and the Lead to 5 mm/rev. In this way, 5,000,000 Motion Counts, or 5 mm worth of screw displacement, is scaled exactly to 16,000 Motor Feedback Counts, or exactly 4 Motor Revs.