In many cases, we need to adopt servo product replacement solutions, such as replacing an existing motor with a new servo motor. Reasons for this may include: product obsolescence, cost savings, delivery time issues, or technology upgrades. A large number of important factors may need to be considered when dealing with the specific context of each application.
1. Healthy Motivation
Regardless of the reason for replacing servo products, the primary task must always be understood and kept in mind: risk reduction. A well-planned replacement strategy can minimize potential problems that may arise during the upgrade process. Failure to carefully manage potential risks during the replacement process will increase the probability of system failure.
Therefore, cost should not be the decisive factor in choosing a replacement solution! A good replacement solution can not only minimize risk but also reduce system costs, rather than reducing costs at the expense of accepting higher potential risks.
2. Shaft stability
Inertia matching is crucial but often overlooked. The replacement servo should have the same rotor inertia as the original servo, or as similarly, as possible. The goal is to maintain system stability after the new servo is installed. Of course, this assumes that the original system has already achieved the required stability.
When replacing a lower-resolution system (such as a tachometer, commutator encoder, or older rotary transformer system), a high-resolution sine encoder feedback device with a resolution of at least 220 lines per revolution (CPR) is typically used. This increases flexibility when matching rotor inertia. Generally, when improving the feedback device resolution with a high-resolution device, the servo inertia should be at least one-third that of the original motor, ideally half. This method has been successfully applied in many fields.
3. Speed and Torque
Speed and torque matching are equally important. The performance of the replacement motor should meet or exceed that of the original motor. Analyzing the product catalog parameters (i.e., continuous torque, rated speed) of both motors to ensure there are no defects is crucial.
Torque values must also be compared across each motor speed range. Comparison graphs are a very helpful practice, allowing you to compare motor speed/torque curves and manually plot the desired values in the datasheet. For example, plotting the continuous torque at 1000 PRM.
Motor A = X Nm and motor B = Y Nm, and perform the same operation across the entire speed range.
4. Motor dimensions
While dimensions aren't particularly critical for motor performance, having a new servo motor with the same mounting dimensions as the original motor during replacement facilitates streamlined operations. The outline drawings of both motors should be analyzed to ensure consistency. Even replacing motors using industry-standard bases (such as NEMA or ICE) is a good approach. Relevant standards generally specify the same guide and bolt ring dimensions, although shaft dimensions are often not fixed. For example, even if you're replacing a NEMA 34 motor, the product definitions from different manufacturers can vary significantly!
5. Other factors
Is the motor the only part of the machine that is replaced? Generally, replacing a servo motor means replacing the driver, cables, and in rare cases, even the controller. In such cases, if the manufacturer's recommendations are followed, then differences in the motor windings can be a secondary consideration.
However, if the replacement motor will be used with the existing driver, a thorough inspection is necessary. For example, winding data (including motor constants: Kt and Ke), feedback device type and resolution, and cable pin layout must be carefully checked and matched. Furthermore, different servo motor manufacturers often use different units and conversion methods for these critical parameters. This can make it difficult to clearly distinguish motor definitions and units during comparisons. This article provides some practical supplementary information in this regard, introducing some common specification differences that should be considered during servo replacement.
