Single Servo or Dual Servo Gantry Drive??

 

Dynatorch, like many vendors offers only dual sided drive systems for the cutting table’s long axis (X axis). The issue here is what are the advantages of each type of drive?

There are two fundamental reasons for considering a dual servo X axis drive system.

First, you may want to eliminate any raised obstacles that may block the easy loading of material onto the table from the table’s long axis side. Using a dual sided drive gives the appearance of a simpler mechanical design.

Second, you may want to add more power to your system by adding a second motor. 

A critical consideration for any gantry design is keeping both ends of the gantry moving in the same direction at the same time. If one end of a gantry is allowed to lag behind, all cuts will be distorted and accuracy impossible to achieve.  Properly designed single servo drive gantries use a spring loaded cross shaft locked to gearing systems on both sides of the table. This cross shafting assures, thorough positive gearing, so that both ends of the gantry CANNOT get out of alignment, nor can they crab walk (where one side lags behind the other).

Dual servo drive systems rely exclusively on each motor staying in perfect synchronization with the other to hold the gantry in alignment. High end servo systems use encoders on each motor to ensure they are electronically coupled (an electronic cross shaft).

Dynatorch's Intelligent Dual servo axes are set up in such a manner.  An instruction is sent to the master motor to move a specified distance. Master motor encoder movement is seen by the slave motor.  The slave motor has been programmed to copy that ACTUAL movement exactly.  This is all performed in software requiring no additional hardware to be tuned or maintained. 

With less sophisticated stepper motor dual drives the same amount of stepper pulses (steps) are sent to each drive motor.  As long as each motor acts on the pulses in the exact same manner the gantry will stay in alignment. The problem here is that stepper motors are notorious for losing steps. When the stepper motor on one side loses steps slightly more than the other side (allowing one side to lag behind the other) the gantry will be pulled out of alignment and cuts will be distorted. The longer you run the stepper drive the more errors accumulate and the more the gantry is pulled out of alignment.

A properly designed single servo drive gantry is simpler, less expensive, very accurate and reliable.  Dual servo systems add cost of a second motor and gearbox, but add power and eliminates the cross shaft that could get in the way.  Also on very long gantries, the cross shaft length becomes an issue with windup and sag. The choice is up to the customer. They both have their advantages.