Avanced Motion Controls servo amp  - Page 1
Forum section: electronics / projects

author: IconicPCB
author_rank: Super Contributor
timestamp: February 27, 2016, 07:47:30 am
content: I am using AMC brushles Servo motor amps model BE25A20.The amp will accept quadrature signal and digest it to form a tacho feedback signal.Problem is the frequency to Voltage circuit outputs 1V/22KHz.My maximum pulse rate is under 10KHz.The tacho signal is used to close the velocity loop. Machine performance is brought into question by the mismatch between the servo amp frequency to voltage converter and the quadrature converter frequency range under normal low speed operation.It wouldn't be so much of a problem if the good folk at Advanced Motion Controls published a more detailied circuit diagram and did not burn ( laser ablate) markings on the chips complement.Plea for help anybody out there with a circuit diagram ?

author: Rerouter
author_rank: Super Contributor
timestamp: February 27, 2016, 07:58:25 am
content: So as i understand from your pulse, you can only generate pulses in the ballpark of 10Khz, but need a quadrature signal in multiples of 22Khz to fully control the system, I assume your controlling the system by some form of microcontroller, so am curious why the 10Khz limit,

author: H.O
author_rank: Frequent Contributor
timestamp: February 27, 2016, 04:38:41 pm
content: AMC does that to their stuff. I have seen various of their models and they've all had ethced/sanded ICs, bastards.Sorry, I don't have a schematic. If you don't find one and AMC won't help then tracing that part of the circuit out and reverse engineer it will be your best bet. Draw the IC as a black box with the surrounding Components, then it might be sort of easy to figure out what it is, like an OP-amp or perhaps an off the shelf F/V converter chip.However, instead of modifying the drives perhaps changing the encoder to one with twice the resolution is the "right" thing to do ? Or make up your own, external, F/V converter and feed the output of that into the normal tacho-input.

author: IconicPCB
author_rank: Super Contributor
timestamp: February 27, 2016, 11:49:51 pm
content: Rerouter,The machine is driven by linear motors using linear glas scale for positional feedback.The glass scale outputs 50 lines per mm in quadrature. The two signals are then further processed to get to an effective 200 line or 5 micron resolution with direction ( of motion ) flag.Top speed during production is 9000mm/min or 9000/60 mm/second.If the specification is read in its simplest form then the at maximum speed the frequency to voltage converter sees 9000/60 *50 lines producing 7.5KHz.If the gains offered by quadrature signal are accounted for then the input frequency is 30KHz.On board F/V converter is specified as 22KHz/V. The inner velocity loop gain gain is set by a 14 turn trim pot. The trim pot needs to be pushed to the end in order to achieve a semblance of a usable loop gain.The pot is used as an adjustable voltage divider hanging from an op amp output to ground while the wiper goes to the inverting input of the op amp. I can lift the pot pin and insert a series "build out" resistor to bring the wiper away from the critical end of wiper position but i would rather the F/V converter produced higher output.I shall have to measure the output of the converter at a known speed to get a better handle on the F/V conversion gain.On the business of deleting chip markings... how many software houses release their binaries or source code to commercial products?All part and parcel of forensic engineering.On the question of increasing input pulse rate..possible but hard to achieve.Sub micron scales are an arm and a leg.Hard to justify.External tacho input preset for +/- 60 V swing ... not so easy to achieveHave entertained possibility of decoding direction and speed information from quadrature pulses and then trying to put together an electronic 1:16 gearbox. Problem is ensuring the gearbox output is indeed at the right ratio, always true quadrature and the the decoded direction is in lock step with actual motion with minimal bunching of pulses.Will need to spend some time on this.