Optics: measuring and testing – By dispersed light spectroscopy – With monochromator structure
Reexamination Certificate
2000-08-21
2003-01-14
Evans, F. L. (Department: 2877)
Optics: measuring and testing
By dispersed light spectroscopy
With monochromator structure
C356S334000
Reexamination Certificate
active
06507399
ABSTRACT:
The invention concerns a device for adjusting angular play on a predetermined angular range of an optical element mobile in rotation relative to a frame. It is notably applicable to driving a diffraction grid in a monochromator system.
Various mechanisms capable of driving and positioning in rotation a mobile optical element are already known, such as sinus bars. Generally, the angular range useful for rotation positioning is limited. For a diffraction grid, notably, it is usually comprised between 5° and 60°. It is interesting, in order to control the orientation of the optical element over this angular range, to make use of a stepping motor, associated with a reduction ratio, so that the number of points on the predetermined angular range is increased. For example, whereas a stepping motor offers a few tens to approx. 400 points per revolution, the reduction ratio enables to cover 1000 points over 30°.
The driving system of the mobile optical element generates however transmission plays which are made even worse in the presence of a large reduction ratio. To obtain accurate positioning, it is therefore necessary to compensate for these plays. A known device for adjusting angular play for a monochromator system in which the diffraction grid is carried by a square, comprises a draw spring mounted on the square. This device only allows for limited rotation of the grid around its rotational axis, because the spring winds around this axis and a microswitch must be placed to avoid damaging the device in case of maloperation.
This device has the shortcoming of a mechanical transmission with limited angular travel. Moreover, the microswitch is necessary to secure the mechanism and involves additional costs. Another shortcoming of this device is that the spring applies to the square a torque that varies substantially over the angular measuring range, which is detrimental to the quality of the play adjustment,
It is an object of this invention to offer a device for adjusting angular play over a predetermined angular range that enables mechanical transmission with unlimited angular travel. This device enables therefore to do away with a microswitch.
The invention concerns such a device that is able to secure transmission at low cost and without any damage.
The device of the invention also enables to obtain a counter-torque to the driving torque with little variation over the whole predetermined angular range.
To this end, the invention applies to a device for adjusting angular play on a predetermined angular range of an optical element mobile in rotation relative to a frame.
According to the invention, the device comprises:
a contact piece integral with this element, and
an elastic steady arm with two ends.
A first of these ends is fixed to the frame. The second end cooperates with the contact piece when the mobile element is oriented in the angular range, at least when the mobile element enters this angular range in an active rotational direction, so that the steady arm exerts on the mobile element a counter-torque. This second end does not co-operate with the contact piece when the mobile element is oriented outside this angular range.
Advantageously, the rotation-mobile optical element is a diffraction grid of a monochromator, carried by a square mobile in rotation around an axis.
The aperture of the angular range is comprised between 5° and 60°.
The orientation of the mobile element is preferably defined using a reference axis integral with the mobile element and rotating with it around the rotational axis of the element. The mobile element is then ‘oriented’ in the angular range when the mobile axis is in this angular range.
The device of the invention enables to exert a counter-torque selectively on the predetermined angular range and to let the mobile element rotate freely around its rotational axis outside this range, thanks to the co-operation of the contact piece and the steady arm. Thus, mechanical transmission has a limited angular travel and the play adjustment is conducted reliably on the angular range.
In certain embodiments, when the mobile element is oriented outside the angular range and enters the same, the play adjustment is performed automatically, whatever the entrance direction of the mobile element in the angular range. Thus, in a peculiar embodiment, the contact piece is arranged in the centre of the mobile element.
In other preferred embodiments, play adjustment is engaged selectively according to the entrance direction of the mobile element in the angular range. Thus, play adjustment can be controlled quite reliably and very accurately, since it is only effective when the angular range is entered in the expected direction.
Thus, preferably, the mobile element has an inactive rotational direction, the second end not co-operating with the contact piece when the mobile element enters the angular range in the inactive rotational direction.
Once the play adjustment is engaged, the mobile element having is entered the angular range in the active rotational direction, the play adjustment continues as long as the mobile element remains oriented in the angular range, regardless of its rotations (and notably their directions) within this range.
Conversely, when the mobile element enters the angular range in the inactive rotational direction, it is subject to a non-extant or very small counter-torque, regardless of its orientation in the angular range.
In the embodiments with active and inactive rotational directions, the device for adjusting play comprises advantageously a reset stop intended to block the steady arm in one displacement direction of the arm matching the inactive rotational direction of the mobile element, so that the counter-torque is greater than a threshold value as soon as the mobile element enters the angular range in the active rotational direction.
This arrangement promotes the preservation of a counter-torque with little variations over the whole angular range, whereas this torque differs from zero as soon as the mobile element enters the angular range.
In this preferred embodiment of the device for adjusting play with active and inactive rotational directions of the mobile element, the device comprises a retractable ramp integral with the mobile element and intended to co-operate with the steady arm when the mobile element enters the angular range in the inactive rotational direction, in order to prevent the steady arm from co-operating with the contact piece while conferring the counter-torque a negligible value
By ‘ramp’ is meant a tilted element with possibly variable slope along a given direction.
The retractable ramp enables to avoid, in the inactive direction, any contact between the mobile element and the steady arm. It implies that the steady arm should be elastic not only on a plane perpendicular to the rotational axis of the mobile element, but also on a plane corresponding to the slope of the ramp. According to a peculiar embodiment in which the ramp extends between the mobile element and the steady arm, both planes are overlapping.
The retractable ramp and the steady arm are such that when the steady arm escapes from the contact piece after overshooting the end position corresponding to the active rotational direction, the steady arm returns beneath the retractable ramp. Thus, the retractable system is again ready to operate in the case of a rotation of the mobile element in the inactive direction.
Preferably, the retractable ramp is rising and extends above the contact piece.
According to other embodiments, the retractable ramp is falling or extends between the contact piece and the steady arm, while being curved towards the contact piece In another embodiment, the contact piece is rigid when it touches the steady arm in the active rotational direction and it is flexible when it touches the steady arm in the inactive rotational direction.
Advantageously, the contact piece and the steady arm are such that the counter-torque exhibits a small relative variation on the angular range, preferably smaller than 25%.
The parameters correspo
Andrieu Philippe
Thevenon Alain
Arent Fox Kintner Plotkin & Kahn
Evans F. L.
Jobin Yvon S.A.
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