DE69128085T2 - Device for determining the position of a device movable along a rail - Google Patents

Description

The present invention relates to a device for use in controlling the air flow through an extraction hood.

The following are applications relating to the present application: EP 0 541 862; EP 0 541 864; and EP 0 541 863.

Fume hoods are used in various laboratory environments to provide a workspace where potentially hazardous chemicals are used, the fume hoods comprising an enclosure having movable doors at its front portion that can be opened to various sizes to allow a person to gain access to the interior of the enclosure for the purpose of conducting experiments and the like. The enclosure is usually connected to an exhaust system to remove any harmful fumes so that the person is not exposed to them when performing work in the fume hood.

Fume hood controllers which control airflow through the fume hood have recently become more sophisticated and are now able to more accurately obtain the desired flow characteristics to vent vapors from the enclosure as a function of the desired average surface velocity of the fume hood opening. Average surface velocity is generally defined as the airflow into the fume hood per square foot of open surface area of the fume hood, the size of the open surface area being dependent upon the position of one or more movable sliding doors provided at the front of the enclosure or fume hood and the size of the bypass openings provided in most types of enclosures once the door or doors are closed. increase or decrease the speed to compensate for the varying size of the opening or area. Alternatively, there may be a single fan connected to the exhaust manifold which in turn is connected to the individual ducts of several extraction hoods and dampers may be provided in the individual ducts to control the flow from the individual ducts, in turn thereby modulating the flow to obtain the desired average area velocity. There may also be a combination of the two systems described above.

The doors of such hoods can be opened by lifting them vertically, often referred to as the sliding position. Some hoods have a number of doors mounted for sliding movement, usually in two sets of tracks. There are even doors that can be moved horizontally and vertically, with the tracks mounted in a frame structure that is vertically movable.

Prior art hood controllers have included sensing devices to measure the absolute position of the vertical doors or the relative positions of the horizontal doors and then use a signal proportional to the sensed position to change the speed of the fans or vary the position of the dampers.

US-A-4 528 898 discloses a device having the features of the preamble of claim 1.

In accordance with the present invention there is provided an apparatus for use in controlling the air flow through an extraction hood to obtain a relatively constant mean surface velocity through an uncovered portion of an opening of an extraction hood of the type having a movable sliding door and adapted to selectively cover at least part of the opening as the sliding door moves, the apparatus being adapted to provide position-indicating signals indicative of the absolute positions of the sliding door, characterized in that the device includes:

an electrical switch means comprising an elongated electrical resistance means having a predetermined resistance value per unit length, mounted parallel to and adjacent to a direction of possible movement of the sliding door;

an actuating means connected to the sliding door and adapted to move as the sliding door is moved, the actuating means positioned to actuate the switch means at a single discrete switch position that changes along the length of the resistance means as the sliding door is moved; and

a circuit means arranged to provide a substantially constant electrical current through a portion of the resistance means between an end portion of the resistance means and the nearest switch position, the circuit means thereby providing a voltage signal having an amplitude proportional to the distance between the end portion of the resistance means and the switch position.

The circuit means can connect the resistance means to ground in any switching position.

The electrical switch means may comprise:

a first elongated thin base member to which the elongated electrical resistance means is applied, the resistance means comprising a strip of resistive ink having a known, substantially constant resistance per unit length printed on the first base member; and

a second elongated, thin base member generally in a superimposed position with respect to the first base member, the second member having a strip of conductive ink applied in close proximity to the strip of resistive ink on the second member, the first and second members being joined in close proximity but spaced apart by a pair of spaced adhesive beads are secured to one another at a distance from one another, the members being adapted to flex toward one another in response to the actuating means to a sufficient extent so that the resistive ink contacts the conductive ink at the switching position.

The electrical switch means preferably has a length that corresponds at least to the length of the travel path of the sliding door.

The extraction hood may be of the type having a vertically movable sliding door, the electrical switch means being vertically oriented, the circuit means thereby providing a voltage signal proportional to the vertical position of the sliding door. In this case, the electrical switch means may be vertically oriented, adjacent to one side of the sliding door, the sliding door having the actuating means mounted thereon in a predetermined position, the electrical switch means extending at least from the actuating means when the sliding door is generally fully closed to the elevation of the actuating means when the sliding door is opened to substantially the full extent of its operative travel.

Alternatively, the apparatus may comprise a plurality of sliding doors for covering the opening, including at least two sliding doors horizontally movable in each of two sets of tracks, each of the sets of tracks having one of the respective such electrical switch means, each of the sliding doors having one of the respective such actuating means, and the circuit means being arranged to provide a generally constant electrical current from the opposite ends of each resistance means at a switch position of each sliding door.

The circuit means may comprise current regulating means connected between a power supply means and the resistance means for controlling, regardless of the position of any of the switching positions along the resistance means, to ensure a substantially constant current through the resistance means. In this case, the voltage signal can be generated between the current control means and the end of the resistance means to which the current control means is connected.

Alternatively, the circuit means may comprise current control means connected between the power supply means and each end of the resistance means for providing a substantially constant current through the portion of the resistance means extending from each end of the nearest switch position, regardless of the position of one or more switch positions.

The current regulating means may comprise a comparator means having an input connected to a reference voltage and another input connected to the emitter of a PNP transistor and through a resistor to the power supply means, the base of the transistor being connected to the output of the comparator means and the collector of the transistor being connected to the resistor means.

The present invention will now be described by way of example with reference to the accompanying drawings, in which:

Fig. 1 is a schematic block diagram of the device according to an example of the present invention, shown integrated with a room controller of a heating, ventilation and air conditioning (hereinafter also HVAC) monitoring and control system of a building;

Fig. 2 is a block diagram of a fume hood controller, shown connected to a control panel, the latter being shown in front view;

Fig. 3 is a schematic front view of the front of a typical extraction hood having vertically operable sliding doors;

Fig. 4 is a schematic front view of the front of a typical extraction hood having horizontally operable sliding doors;

Fig. 5 is a cross-section taken generally along the Line 5-5 of Fig. 4;

Fig. 6 is a schematic front view of the front of a typical combination sliding extraction hood having horizontally and vertically operable sliding doors;

Fig. 7 is an electrical schematic diagram of a switch means indicating a plurality of sliding door positions;

Fig. 8 is a cross-section of the sliding door position switch means; and

Fig. 9 is a schematic diagram of an electrical circuit for determining the position of the sliding doors of the extraction hood.

It should be generally understood that a fume hood controller controls the air flow through the fume hood in a manner whereby the effective size of the total opening with respect to the fume hood - including the portion of the opening uncovered by one or more sliding doors - will have a relatively constant average surface velocity of the air moving into the fume hood. This means that, regardless of the area of the uncovered opening, an average amount of air per unit surface area of the uncovered portion is moved into the fume hood. This protects the persons in the laboratory from being exposed to noxious fumes or the like since air is always flowing into the fume hood and out of the exhaust duct, and the flow is preferably controlled at a predetermined rate of approximately 23 to 38 m³ per minute per m² (75 to 125 cubic feet per minute per square foot) of effective surface area of the uncovered opening. In other words, when the sliding door or doors are moved to the maximum opening position, which gives an operator the best access to the interior of the hood to conduct experiments or the like, the air flow will most likely have to be increased to maintain the average surface velocity at the predetermined desired level. The performance and effectiveness of various prior art controllers vary differ considerably from each other.

The present invention is particularly useful for laboratory fume hoods of the type having a controller for controlling the air flow through the fume hood to obtain an average surface velocity of air moving into the fume hood which is a function of the size or area of the openings, which in turn is in part a function of the positions of the sliding doors of the fume hood. Since it is highly desirable for the exhaust hood controller to provide very rapid and efficient control of the average face velocity of the exhaust hood and to achieve and maintain the desired average face velocity within a few seconds after one or more doors covering the front opening of the exhaust hood are moved, it is necessary that the position of the doors be determined quickly and accurately and therefore the present invention generally provides continuous voltage signals which are input to an exhaust hood controller which uses the signals to control the flow of air into and out of the exhaust hood.

Returning to the drawings and specifically to Fig. 1, there is shown a block diagram of a plurality of fume hood controllers 20 connected to a room controller 22, an exhaust controller 24, which may be part of the room controller itself, and a main control console. The fume hood controllers 20 are connected to the room controller 22 and the exhaust controller 24 and the main control console 26 in a local area network (LAN) illustrated by line 28, which may be a multi-conductor cable or the like. The room controller 22, exhaust controller 24, and the main control console 26 are typically part of the building main HVAC system in which the laboratory spaces containing the fume hoods are located. The suction hood controllers 20 are supplied with a current through a line 30 which has a suitable voltage via a transformer 32 or the like.

Referring to Fig. 2, a hood controller 20 is illustrated with its input and output connections connections, and the fume hood controller 20 is connected to a control panel 34. It should be understood that each fume hood will be provided with a fume hood controller 20 and that a control panel is provided for each fume hood controller. The control panel 34 is provided for each fume hood and is connected to the fume hood controller 20 by a line 36 which preferably comprises an eight conductor multi-conductor cable. The control panel has a connector 38 such as a 6-wire RJ111 type telephone jack to which a laptop PC or the like is connected for the purpose of entering information concerning the configuration or operation of the fume hood during initial installation or for changing certain operating parameters (if necessary). The control panel 34 is preferably mounted on the fume hood in a convenient position which is arranged to be easily observed by a person working with the fume hood.

The exhaust hood controller control panel 34 includes a liquid crystal display 40 which, when selectively actuated, provides visual indication of various operational aspects of the exhaust hood including three digits 42 indicating the average face speed. The display 40 illustrates other conditions such as low face speed, high face speed and an emergency condition and controller fault indication. The control panel may include an alarm 44 and an emergency drain push button 46 which the operator may press to drain the exhaust hood in the event of an accident. The control panel has two auxiliary switches 48 including a day and night operating mode which may be used for various customer requirements. It is contemplated that the nighttime mode of operation should have a different and preferably reduced mean area velocity, presumably because no one would be working in the area and such a lower mean area velocity would conserve energy. An alarm sleep switch 50 is preferably also provided.

Extraction hoods come in a variety of styles, sizes and configurations, including those that have a single sliding door or a series of sliding doors, with the sliding doors able to move vertically, horizontally or in both directions. In addition, different extraction hoods allow for different bypass flow rates, i.e., have openings that allow a flow rate that will continue even when all sliding doors are as fully closed as their design allows.

Referring to Fig. 3, there is shown a fume hood, generally designated 60, having a vertically operated sliding door 62 which can be moved to gain access to the exhaust hood and which can be moved to the substantially closed position shown. Some types of exhaust hoods have a bypass opening located above the sliding door, while others are located below it. In some exhaust hoods, for example, the first movement of a sliding door will enlarge the opening at the bottom of the door shown in Fig. 3; however, as the door is raised, the bypass opening is primarily blocked so that the effective size of the total opening of the exhaust hood is held constant for perhaps the first quarter of the movement of the sliding door 62 through its travel distance.

Other types of exhaust hoods may include a plurality of horizontally movable sliding doors 66, such as those shown in Figs. 4 and 5, wherein the doors may be moved in upper and lower adjacent tracks 68. When the doors are positioned as shown in Figs. 4 and 5, the exhaust hood opening is completely closed and an operator may move the doors in the horizontal direction to gain access to the exhaust hood. Both exhaust hoods 60 and 64 have an exhaust duct 70 that generally extends into an exhaust system, which may be the system of the HVAC equipment previously described. The exhaust hood 64 also includes a filter assembly shown schematically at 72, the filter assembly being designed to prevent harmful smoke and other contaminants from exiting the exhaust hood into the exhaust system. Referring to Fig. 6, a combination exhaust hood is shown having horizontally movable doors 76 similar to doors 66, the exhaust hood 74 having a frame structure 78 supporting the doors 76 in matching tracks, the frame structure 78 also being vertically movable within the opening of the exhaust hood.

The illustration of Fig. 6 has portions removed, as shown by the dashed lines 73, to illustrate that the height of the exhaust hood may be greater than otherwise shown so that the frame structure 78 may be raised sufficiently to allow convenient access to the interior of the exhaust hood by a person. There is generally a bypass area, indicated as the vertical area 75, and there is usually an upper lip portion 77 which may be approximately 5 cm (2 inches) wide. This dimension is preferably determined so that its effect can be taken into account in calculating the open surface area.

Although not specifically illustrated, other combinations are also possible, including multiple sets of vertically movable sliding doors positioned adjacent to each other along the width of the hood opening, with two or more sliding doors being able to move vertically in adjacent tracks, much in the same way as with residential sliding windows.

The exhaust hood controller is designed to control virtually all of the different types and styles of exhaust hoods available on the market and therefore includes a number of input and output ports (lines, connectors or connections, all of which are considered equivalent for the purposes of describing the present invention) which can be connected to various sensors that can be used in conjunction with the controller. As shown in Fig. 2, there are five slide position sensor ports that are used in sensing the position of both the horizontally and vertically movable sliding doors.

To determine the position of the sliding doors, a Sliding position sensor means embodying the present invention is provided adjacent each of the movable sliding doors and is shown generally in Figures 7, 8 and 9. Referring to Figure 8, the sliding door position indicator comprises an elongated switch mechanism 80 of relatively simple mechanical construction, preferably consisting of a relatively thin polyester base layer 82 having printed thereon a strip of electrically resistive ink 84 of known constant resistance per unit length. A further polyester base layer 86 is provided having a strip of electrically conductive ink 88 printed thereon. The two base layers 82 and 86 are adhesively joined by two adhesive beads 90 located on opposite sides of the strip. The base layers are preferably approximately five thousandths of an inch thick and the beads are approximately two thousandths of an inch thick, with the edges providing a spaced area between the conductive and resistive layers 88 and 84. The switching mechanism 80 is preferably secured to the exhaust hood by an adhesive layer 92.

The polyester material is elastic enough to allow one layer to be moved toward the other so that contact is made in response to a preferably spring biased actuator 94 carried by the mating sliding door to which the strip is mounted adjacent, so that when the sliding door is moved, the actuator 94 moves along the switch mechanism 80 and provides contact between the resistive and conductive layers which are then sensed by the electrical circuits to be described below which provide a voltage output which in turn indicates the position of the actuator 94 along the length of the switch means. In other words, the actuator 94 is carried by the door and provides thereto an electrical voltage which indicates the position of the sliding door.

The actuating means 94 is preferably spring-biased in the direction of the switching mechanism 80 so that when the door is moved, sufficient pressure is applied to the switch means to bring the two base layers together so that the resistive and conductive layers make electrical contact with each other, and the voltage level is provided when this is done. If the switch means is sufficiently long to accommodate the full extent of the sliding door travel as shown in Fig. 3, an accurate determination of the absolute sliding door position can then be made.

It should be understood that the representation of the switch mechanism 80 in Figs. 3 and 5 is intended to be a schematic one; that is, the switch mechanism is preferably actually located within the sliding door frame itself and accordingly would not be seen as shown. The width and thickness dimensions of the switch mechanism are so small that interference with the operation of the sliding door is unlikely to occur. The actuating means 94 may also be placed in a small hole drilled in the sliding door or it may be mounted externally at one end thereof so that it can be in position to actuate the switch 80. In the views shown in Figs. 3 and 6, a switching mechanism 80 is preferably provided in one side or the other of the sliding door frame, whereas in the extractor hoods with horizontally movable sliding doors it is preferred that the switching mechanism 80 be placed in the upper end of the rails 68 so that the weight of the movable doors does not actuate or otherwise damage the switching mechanism 80. It is also preferred that the actuating means 94 be located at one end of each door, for reasons described in the cross-referenced application EP 541 864.

Returning to Fig. 9, the preferred electrical circuit is illustrated which generates the voltage indicating position, which circuit is designed to provide two separate voltages indicating the position of the two sliding doors in a single track. Referring to the cross-section shown in Fig. 5, there are two horizontal rails, each of which supports two sliding doors, and a switching mechanism 80 is provided for each of the rails as well as a circuit shown in Fig. 9, thereby providing a different voltage for each of the four sliding doors.

The switch means is preferably attached to the extraction hood by an adhesive layer 92 and the actuating means 94 is adapted to rest on the switch means at positions along its length. Referring to Figure 7, a schematic representation of a pair of switch means is illustrated as may occur in relation to the two rails shown in Figure 5. A switch mechanism 80 is provided with each rail and the four arrows shown represent the point of contact created by the actuating means 94 which in turn causes a signal to be applied to each end of each switch means, the amplitude of the signal being a voltage proportional to the distance between the end and the nearest arrow. Thus, a single switch mechanism 80 is adapted to provide signals indicative of the position for two doors located in each rail. The circuit used to effect the voltage generation is shown in Fig. 9 and comprises one of these circuits for each rail. The resistive element is designated 84 and the conductive element 88 is also shown connected to ground, the two arrows shown showing the point of contact between the resistive and conductive elements created by each actuator means 94 connected to the two separate doors. The circuit comprises an operational amplifier 100 having its output connected to the base of a PNP transistor 102, the emitter of which is connected to a positive voltage source through resistor 104 to the inverting input of the operational amplifier, the non-inverting input of which is in turn also connected to a positive voltage source of preferably approximately five volts. The collector of transistor 102 is connected to one end of resistive element 84 and has an output line 106 on which the voltage indicative of the position of the door is produced.

The circuit operates to provide a constant current that is directed into the resistive element 84, and this current results in a voltage on the line 106 that is proportional to the resistance value between the collector and ground, which then changes as the closest point of contact with the resistor changes. The op-amp operates to try to drive the inverting input to match the voltage level at the non-inverting input, and this results in the current applied to the output of the op-amp being directly proportional to the effective length of the resistive strip 84. The lower portion of the circuit operates in the same manner as that described and similarly produces a voltage on an output line 108 which is proportional to the distance between the connected end of the resistive element 84 and the point of contact made by the actuator means 94 connected to the other sliding door in the track.

From the foregoing description, an improved sensor means for determining the position of sliding doors is provided which offers advantages over the prior art. Although the switch means 80 is provided for each rail, the unique circuit enables position indicating voltages to be generated for two sliding doors movable in a single set of rails. The device is simple to install and generates the signals using a minimum of components which contribute to the extremely low manufacturing cost.

Claims (12)

1. An apparatus for use in controlling the flow of air through an exhaust hood to obtain a relatively constant average surface velocity through an uncovered portion of an opening of an exhaust hood (60, 64 or 74) of the type having a movable sliding door (62, 66 or 76) adapted to selectively cover at least a portion of the opening during movement of the sliding door, the apparatus being adapted to provide position indicating signals indicative of the absolute positions of the sliding door; characterized in that the apparatus comprises: an electrical switch means (80) comprising an elongated electrical resistance means (84) having a predetermined resistance value per unit length, arranged adjacent and parallel to a direction of possible movement of the sliding door (62, 66 or 76); an actuating means (94) connected to the sliding door and adapted to move when the sliding door is moved, the actuating means being positioned to actuate the switch means (80) in a single discrete switch position that changes along the length of the resistance means (84) when the sliding door is moved; and a circuit means (100, 102, 104, 106, 108) configured to provide a substantially constant electrical current through a portion of the resistance means (84) between an end portion of the resistance means and the closest switching position, the circuit means thereby providing a voltage signal having an amplitude proportional to the distance between the end portion of the resistance means (84) and the switching position. 2. An apparatus according to claim 1, wherein the circuit means (100, 102, 104, 106, 108) connects the resistance means (84) to ground at each switching position. 3. A device according to claim 1 or 2, wherein the electrical switch means (80) comprises: a first elongated thin base member (82) to which the elongated electrical resistance means (84) is applied, the resistance means comprising a strip of resistive ink of a known, substantially constant resistance per unit length printed on the first base member; and a second elongated, thin base member (86) in a superimposed position with respect to the first base member (82), the second member having a strip of conductive ink (88) applied in close proximity to the strip of resistive ink (84) on the second member, the first and second members (82, 86) being secured to one another in close proximity but spaced apart by a pair of spaced adhesive beads (90), the members being adapted to flex toward one another in response to the actuating means (94) to a sufficient extent so that the resistive ink (84) contacts the conductive ink (88) at the switch position. 4. An apparatus according to any preceding claim, wherein the electrical switch means (80) has a length which corresponds to at least the length of travel of the sliding door (62, 66 or 76). 5. An apparatus according to any preceding claim, wherein the extraction hood (60 or 74) is of the type having a vertically movable sliding door (62 or 76) and wherein the electrical switch means (80) is vertically oriented, the circuit means thereby providing a voltage signal proportional to the vertical position of the sliding door. 6. An apparatus according to claim 5, wherein the electrical switch means (80) is vertically aligned adjacent to a side of the sliding door (62 or 76), the sliding door having the actuating means (94) mounted thereon at a predetermined location, the electrical switch means (80) extending at least from the actuating means (94) when the sliding door (62 or 76) is generally fully closed to the elevation of the actuating means (94) when the sliding door (62 or 76) is opened to substantially the full extent of its travel. 7. An apparatus according to any one of claims 1 to 4, including a plurality of such sliding doors covering the opening, comprising at least two sliding doors (66) which can be moved horizontally in each of two sets of rails (68), each of the sets of rails each having one of the respective such electrical switch means (84), each sliding door having one of the respective such actuating means (94), and wherein the circuit means (100, 102, 104, 106, 108) is arranged to provide a generally constant electrical current from opposite ends of each resistance means (84) up to the switching position of each sliding door. 8. An apparatus according to any preceding claim, wherein the circuit means (100, 102, 104, 106, 108) comprises current control means (100, 102) connected between the power supply means and the resistance means (84) for providing a substantially constant current through the resistance means regardless of the position of any switch position along the resistance means 9. A device according to claim 8, wherein the voltage signal is generated between the current control means (100, 102) and the end of the resistance means (84) to which the current control means (100, 102) is connected. 10. A device according to any one of claims 1 to 7, wherein the circuit means (100, 102, 104, 106, 108) comprises a current control means (100, 102) connected between the power supply means and each end of the resistance means (84) for providing a substantially constant current through the portion of the resistance means (84) extending from each end of the nearest switch position, regardless of the position of one or more switch positions. 11. An apparatus according to any one of claims 8 to 10, wherein the current control means (100, 102) comprises a comparator means (100) having an input connected to a reference voltage and another input connected to the emitter of a PNP transistor (102) and through a resistor (104) to the power supply means, the base of the transistor (102) being connected to the output of the comparator means (100) and the collector of the transistor (102) being connected to the resistor means (84). 12. An apparatus according to claim 7 or any of claims 8 to 11 when dependent on claim 7, wherein the rails (68) are located in a common frame means, the frame means being vertically movable with respect to the opening of the extraction hood (64).