A variable-speed upstream conveyor can provide the master motion reference for a servo mechanism. The available evidence supports two candidate architectures: measure the incremental encoder in the PLC and generate a proportional pulse command, or connect the encoder to a compatible external command input on the servo drive. The drive model, encoder electrical interface, pulse format, and supported command modes are not specified, so verify those items before selecting the architecture.
Select the synchronization architecture
| Architecture | Signal path | Engineering decision |
|---|---|---|
| PLC-based tracking | External encoder → PLC measurement → scaling → servo pulse command | Use only if the PLC can acquire the encoder and update the servo command with sufficient stability for the mechanism. |
| Drive-based tracking | External encoder → servo drive command input | Prefer this path when the selected drive explicitly supports the encoder signal and command mode required for master-following operation. |
The source asks whether a Delta servo drive can accept an encoder independently of the motor feedback encoder, such as an MPG input. That capability is model-dependent and is not confirmed by the evidence. Do not assume that an available pulse input accepts the encoder's electrical levels or performs the required synchronization.
Scale encoder motion into servo motion
Define the required mechanical relationship before programming. For proportional pulse following, express the command frequency symbolically as:
servo_command_frequency = encoder_frequency × motion_ratioThe motion ratio must include the required product-to-mechanism speed relationship and the pulse-to-motion scaling of both axes. Encoder pulse count alone represents displacement; speed requires the change in count over a known measurement interval. The evidence does not provide encoder resolution, mechanics, measurement interval, or servo command scaling, so a numeric ratio cannot be calculated.
Evaluate the PLC measurement path
The proposed PLC method uses an encoder-speed instruction such as SPD, mathematical scaling, and a pulse-output command. This can make the servo command follow encoder frequency without operator intervention, but stability depends on the complete acquisition-and-command path. Confirm that the encoder input remains valid over the operating speed range, then evaluate measurement update behavior, command refresh behavior, and the resulting motion during the upstream line's slow start and later speed increase.
A suggested PLC feature in the evidence is the existing CSFO command for an MPG application. Review that command in the documentation for the exact PLC in use. The evidence does not establish its operands, supported hardware, timing, or suitability for continuous production-line synchronization.
Commission and verify the selected path
- Record encoder count and calculated frequency while the upstream line starts slowly, accelerates, and reaches its operator-selected constant speed.
- Apply the defined motion ratio through either the PLC-generated pulse command or a drive-supported external pulse command mode.
- Compare upstream product motion with servo mechanism motion throughout the transition, not only at constant speed.
- Check whether position error accumulates after repeated speed changes. If it does, recheck pulse scaling, signal acquisition, and command-path behavior before changing the ratio.
Use measured synchronization error as the acceptance criterion. A displayed speed match alone does not prove that the mechanism remains aligned with the product.
FAQ
Can a PLC change servo speed from incremental encoder pulses automatically?
Yes, as an architecture: measure encoder count change over a known interval, scale the resulting frequency, and update the servo pulse command. Whether it is stable enough depends on the unspecified PLC input and output behavior and must be verified on the selected hardware.
Can a Delta servo drive follow an external encoder directly?
The evidence does not confirm this for a specific Delta model. Check whether the selected drive provides an external pulse or MPG command input compatible with the encoder's electrical interface and required command mode.
Is encoder pulse count enough to synchronize servo speed?
No. Pulse count gives displacement; speed requires count change over a defined measurement interval. Apply the required motion ratio, then verify that no alignment error accumulates during speed changes.