Iris Motor in a Camera

I think some of them don't have any, they use information form whatever ima ge sensor it uses.

The ones that do, I'd bet it's nothing more than a variable resistor. Any t ype of rotary encoder for that applicaton, to give absolute position like t he resistor would, would be more comlplex. since they always try to do thin gs as cheaply as possible, I would bet on the variable resistor.

If it only has four wirs, what else could it be ?

afaict tell they basically work like a moving coil meter, and the feedback winding just gives you a voltage proportional to speed

-Lasse

Thanks, Lasse! ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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| San Tan Valley, AZ 85142     Skype: skypeanalog  |             | 
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I love to cook with wine.     Sometimes I even put it in the food.

Speed of an iris motor ?

I've only seen the two coil type with one winding as feedback, and a few professional systems with DC motors.

Behave yourself Jim, and I might just drop one in the mail for you Monday.

I do recall a few boards with a dedicated analog exposure control chip.

Steve R.

yes while it is moving

with feedback you can tweak the response

-Lasse

Unless it's a very low volume camera, the motor is probably custom made; you won't be able to get a data sheet. You might be able to get data sheets for similar motors but there is no guarantee how closely yours will match. You might try contacting the camera manufacturer; they might be sympathetic, but that isn't likely.

Your best bet is to test the motor and develop your own data.

Jim Mueller

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That would be sufficient for good control.

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Tim Wescott 
Control system and signal processing consulting 
www.wescottdesign.com

Found this snipit...

The DC iris has two coils, one to move the iris and the other to provide velocity feedback. The moving part of the iris has a magnet and is normally held closed by a light spring. The driving coil opens the iris against the spring somewhat proportional to current supplied, while the other generates a small current proportional to the iris velocity.

and a schematic...

Cheers

Thanks, Martin! ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142     Skype: skypeanalog  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
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I love to cook with wine.     Sometimes I even put it in the food.

Jim,

This splits three ways... Professional cameras with small geared down DC m otors, ie Sony broadcast.

Then for closed circuit TV:

I Quote from a security forum:

Quote

Video Type Lens: This type of auto iris lens contains internal amplifier circuitry to conver t the video signal from the camera into iris motor control. This is the older style lens which is usually larger than its counterpart.

DC Type Lens: This type of auto iris lens is driven by a reference voltage produced by th e camera. The lens contains a driving motor to open and close the lens. In effect the camera contains the iris amplifier and operates the iris moto rs. Less expensive and smaller than the video type lens.

End Quote.

In all of the with coils that I've torn apart, its almost always driven by a meter movement type pair of coils pivoting around a cylindrical magnet . Your basic D'Arsenval movement without the external pole pieces. One coil is driven, the other is for deriving velocity for PID. Some of them have a difference network that senses current through the drive coil, compared to a tapped resistive load driven off the drive amplifier. The AC coupled D ifference between the resistive load and the inductive load current (Looks Sort of like a Whetstone bridge circuit) is used for negative feedback to d erive damping.

Steve

The BabyBird (GooGull) sez: [PDF] Auto-iris Motorized Zoom Lenses - Bosch Security Systems resource.boschsecurity.com/.../Data_sheet_enUS_2191260299.pdf camera optic features. Lenses in this series include 10x, 15x, and

20x zoom range models. Some models provide optional pre- position and manual iris override ... *** Covers the lenses, not the motors. [PDF] D22x9.1B-Y41 - Fujifilm ./pdf/.../d22x91b-y41_e.pdf Fujifilm Wiring. D22x9.1B-Y41. Focal Length ?mm?. 9.1 - 200(22x). Iris Range. F1.2 - T1500(Equivalent to F1500). Operation. Zoom. Motor Drive. Focus. Motor Drive. Iris. *** Useless for your needs; one pager,lens wiring. *** Next 2 are for the drivers, and maybe useful. [PDF] AN41908A - Semiconductor ./AN41908A_AE... Panasonic Corporation AN41908A is a lens motor driver IC for camcorder and security-camera featuring the functions of Iris control. ..... Register input / output signal specification. SCLK. [PDF] AN41919A - Semiconductor ./AN41919A_E.p... Panasonic Corporation AN41919A is a DC IRIS control LSI for IP camera and security ... and is able to control various IRIS motors. Notes) ..... Register input / output signal specification.

..That is the first 4 of a number of hits. If the info in the semi datasheets are insufficient, then try to find out what stepper motors are used,and attack their datasheets.

I've cracked some lenses open and the iris was just a stepper motor with no feedback. Much like old floppy disk heads, they banged up against a stopper to initialize the position every time the aperture opens to full. Closing the aperture was just counting steps.

I don't think I've seen a motor with internal feedback in anything except RC servos. They're expensive and they make assembly difficult. Precision movement usually comes from a stepper motor or optics counting painted lines on the final driven component.

What good are truncated links?

Do you know about

? ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142     Skype: skypeanalog  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

I've seen two types of iris motors..

1. A two phase much like a stepper where one coil becomes the mover and the other a sensor for move detection, then they alternate their jobs where is the other coil then becomes the mover and the first one is now the sensor. There is what looks like a spur ring gear and two little coils off the side which are the A and B phase and sensors shared.

3. The spring type. tension spring keeps the iris in one position when power is off. There is a PM that is attached to the linkage of the iris and a coil near by that pulls it. Position is proportional to magnetic strength in the coil. Also, the second coil is the damper coil, this coil has DC current proportional to the velocity of the shutter to create drag so not to allow iris to over shoot or wobble at the stop point.

I am sure there maybe constant DC in the damper coil to prevent it from shaking with normal handling.

I am sure there are other types out there like a PM motor directly driving the iris. A lot of these camera's use the image center to adjust the iris, they just open/close as they see fit from the image sensor and use over current detection for stops or jam detection, which may get mistaken for iris limits.

You need to research which system you're interested in. Maybe you're trying to do all of them in a single chip?

Jamie

via

feedback

It is likely to work differently between still cameras and video cameras.

?-)

Thinking about it some more, for a video camera it is likely to a torquer motor instead of a normal motor.

?-)

it's just an example of what you could have got from google.

tinyurl makes temporary links.

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An example of the two coil type just left here priority mail to the S.T. valley. No big deal, the board camera it was on is quite dead, with no V Sync.

Steve R.