Sujet : Re: Motor Speed Control
De : bill.sloman (at) *nospam* ieee.org (Bill Sloman)
Groupes : sci.electronics.designDate : 09. Mar 2024, 06:42:50
Autres entêtes
Organisation : A noiseless patient Spider
Message-ID : <usgpca$25ov0$1@dont-email.me>
References : 1 2 3 4 5 6 7 8 9 10 11 12
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On 9/03/2024 5:49 am, KevinJ93 wrote:
On 3/7/24 8:48 PM, Bill Sloman wrote:
On 8/03/2024 7:13 am, KevinJ93 wrote:
...
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Not in 1970. Even after that time they did not possess any advantage over DC motor drive with speed stabilization based on back-emf.
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Don't be silly. Back-emf depends on the strenght of the magnetic field generating the basck-emf, and that is temperature dependent.
At about 0.2% per deg the magnetic field strength stability was adequate for the speed accuracy required under the required environmental conditions.
Motors run hotter than their environment
Synchronous motors rotate at a rate that reflects the stability of the frequency source that determines the drive frequency, and reasonably stable frequency source - watch crystals have been around for ages.
Even for AC powered units where power was not an issue stepper motors were never used. Synchronous motors with synthesized drive were occasionally a feature but many/most used back-emf stabilization with DC motors.
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ICs were available to integrate that circuitry:
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eg https://www.precisionmicrodrives.com/ab-026
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Even implementing the discrete drive electronics would be more costly than necessary at a time where individual transistors were a significant cost; Philips' solution used two transistors - creating a divide by 4 plus driver transistors plus an oscillator would probably require about ten transistors plus numerous other components.
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Which you could could buy in an integrated circuit. Most of mine were in a chunk of PROM.
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Not in 1970. Even by the late 70's a bipolar (P)ROM would use up all your power budget.
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It didn't - and it wasn't bipolar.
MOS EPROMS such as the 1702 were cumbersome to use with multiple supplies required.
It was one-time programmable, not an EPROM.
The logic to drive them would have been TTL consuming significant amounts of power as well as expensive.
CMOS was around and cheap. I'd first used it around 1975, and the price fell by a factor of three as I was developing the 1975 circuit.
The first EPROMS that were easy to use, such as the 2708 weren't widely available till the late 70's.
The stepper motor circuit that I worked on was developed in 1978.
<snip>
-- Bill Sloman, Sydney
Re: Motor Speed Control
Re: Motor Speed Control