This is a question that I get all the time, related to the “What is Obsolete” question. There are 3 situations where you upgrade motion control (or control systems in general).
1. Absolute Obsolescence. The controls are no longer available, no longer repairable and the machine is still required. This is a no-brainer. If the control goes down at this point you are dead in the water until the upgrade is done. Wouldn’t you really rather schedule that instead? However, be sure you know the control is actually Absolutely Obsolete, don’t take a used car salesman’s word.
2. Performance Requirement Change. The controls will not perform to a change in specification, or production. This is different from the controls can’t match their previous performance, which may mean a control issue (or mechanical one). Beware speed upgrades, as often times the physical machinery cannot handle the speed increase that production would like.
3. Economic Obsolescence. This one is tricky. I get a lot of “That’s too expensive, I will just upgrade to something newer” in my job. This statement is typically made by someone who has no idea either of what the current system is doing (I had one guy insist that the job that a 3 axis servo system was doing could be done by 3 pwm drives, his replacement called me to get the drives repaired and refitted into the machine), or who has given no thought to the requirements of the replacement. A fine example is TDM series drives. The drives and motors are still repairable, but are expensive to get done. A retrofit looks easy, as the TDM drives take a standard +/-10v servo signal for control, but it turns out that the units also are typically powered by 230 volt, and the motors cannot be run by anything else. So, you are ripping out the drives, motors and cabling, rewiring the cabinet for 480 and reworking the control system to accept the new drive’s ready and enable setups. I have done this in a couple of days with a good electrical crew, but I have been doing this for 30 years too.
The other thing to think of is that the best time to upgrade your servo system is as late in the life of the system as possible. This makes sure of two things. One, you get the money out of the old system, and two, you get as new of a system as possible. Servo systems families typically change every 7 to 10 years, depending on the manufacturer. Upgrading at the year before the entire family change takes place means that a year from now you will have the non-current system. It is a lot like buying computers. This week’s star is next weeks dog, so wait as long as possible and then plant your flag, knowing that soon this too will be a legacy system.