Controls System for a Chamfer / Stamper

The replacement of a VFD is a straightforward DFMA (Design for Manufacture & Assembly) redesign with three constraints; form, fit and function. The form and fit constraints of the drive replacement on an already overpopulated panel were easy. The function constraint of the replacement drive proved more challenging. The Variable Frequency Drive employed for the spindle served not only as a drive, but provided the logic control for the machine process / sequence.

The manufacturer of the obsolete drive gave assurances that they had a ‘drop-in' replacement drive. The redesign proceeded with that assurance along with the following requirements:

Machine function and capabilities to be retained:

• Automated stud chamfering and stamping (marking)
• Ability to stamp one, both, or neither end of the stud (selectable from HMI)
• Machine cycle initiated though either foot switch or proximity switch found in stamping unit (selectable from HMI)
• A machine cycle counter
• Spindle Speed Changeable from HMI
• Ability to force each solenoid manually for troubleshooting
• Troubleshooting and Maintenance in the HMI
• Job Cycle Counter

Project Scope:

• Provide a replacement VFD with logic capability
• Keep existing back panel design as to not incur changes to machine housing
• Keep panels' pluggable design such that it can be replaced in field in event of component failure
• Keep repeatability and precision of chamfer depth
• Keep HMI the same
• Keep ease of assembly and cost in line with prior design for repeat production.

Upon completion of the redesign and subsequent 1st piece build, functionality testing began on a machine in which the original design of the control panel was removed and replaced with the 1st piece redesign panel. Initial testing moved along rapidly until the chamfering phase of testing where it became apparent there was an issue with repeatable chamfering of the fastener. After considerable investigation and continued testing, it was determined that the logic scan time of the replacement drive was too slow to provide repeatable chamfers.

With less than a week to provide the replacement controls package, we'd hit a considerable hurdle to meet our deadline. After a high pressure brainstorming session and an availability check on stock, we moved forward with an alternate solution. The replacement drive would be used (minus the optional logic module) as a "dumb" drive for spindle speed and a Koyo DL05 PLC would handle the machine operations and spindle speed reference shown in the panel below:

The resolution, with minimal panel modifications, was mounting a Koyo DL05 with an optional analog card on the panel to an existing DIN rail. The DL05 PLC provided:

1. A cost that was a wash with that of the accessories required to make the VFD logic capable.
2. Porting of the program from the obsolete VFD ladder to the DL05 was quick and easy.
3. The scan time of the DL05 exceeded needs for making machine chamfering repeatable enough for the application.
4. The small footprint of the DL05 made fitting it onto the existing panel with limited real estate feasible.
5. The available EEPROM provided the ability to hold the cycle counter during long shutdowns.
   a. Cycle count could be secured and
   b. The machine cycle count could be moved from volatile memory to non-volatile memory on shutdown and from non-volatile to volatile memory on the first scan.
6. The Modbus feature made for easy transitioning in the HMI program. The existing HMI needed information from both the PLC and VFD. The only way to achieve that was using both communications ports available on the HMI via modbus. One with the RS-232 port (Koyo) and one with the RS-485 port (VFD). This was accomplished with no additional hardware and
7. An analog module for 1-10v speed reference to the VFD for spindle speed. The DL05 single slot and available analog card allowed easy program additions and wiring to replace the speed control previously done directly from the HMI to the obsolete VFD.