EP1398292A1 - Control device for lifting platforms - Google Patents

Abstract

Control device for a lifting platform has: ultrasonic transmitter (1) and receiver (2) for measuring the height of the platform; an evaluation unit (3) that processes the signals from transmitter and receiver to determine platform height (h); at least one actuator (5) for raising or lowering the platform and a control unit (4) that controls the actuator based on the measured height and a height that is to be set. The invention also relates to a corresponding lifting platform or ramp for a motor vehicle that is equipped with an inventive control device.

Description

The invention relates to a control device for lifting platforms, which detects a lifting height h of the lifting platform and adjusts it according to a predetermined target height H ₀ .

Lifts, especially for vehicles, usually have one or several lifting units for lifting or lowering a platform, on which the object to be lifted stands. Known Lifting units are, for example, punch or scissor hoists.

A vehicle to be lifted is placed on a single or multi-part platform the lift (driving surface), which is used to work on the Vehicle is lifted by the lifting unit (s). The vehicle can also be lifted from a structure, with a or grab several support arms under the vehicle and lift it. Some lifts have the for each axle or wheel to be lifted vehicle provided a separate lifting unit.

In order to lift the body to be lifted to a predetermined lifting height, it is necessary to increase the height of the platform or structure to capture. In known measuring devices for detecting the lifting height are mechanical or optical markers from a corresponding Sensor detected and evaluated. The lifting height can then based on the number of waymarks passing the sensor be determined. This method of incremental displacement measurement has the disadvantage, however, that a large number of lifting heights of evenly arranged waymarks over a long distance must be attached, which reduces the manufacturing costs and Production costs for the lift increase. Furthermore, the maximum resolution of the measuring device by the distance of the Markers determined. Is the measuring section by mechanical lever mechanisms, Lever arms or cables are also reduced the path resolution of the measuring device.

EP 0 866 306 describes a device for distance measurement, where a friction wheel rolls on a cylinder piston rod. With this non-form-fitting path measurement it can, however Pollution will cause slip problems, especially on one smooth, oily cylinder rod of a lifting cylinder.

In particular, for the wheel alignment of vehicles is an accurate Positioning of the individual driving surfaces or structures with a maximum deviation of less than 1 mm is required. For a corresponding one Control or regulation of the lifting units is for this a precise measurement of the lifting height is necessary. This can be done with the known Devices for measuring and controlling the lift cannot be achieved with sufficient accuracy.

There is also a lift with several separate lifting units the problem of synchronizing the individual lifting units. In known lifting platforms, this is done via a mechanical connection between the lifting units, the platforms and / or the Structures. For example, structures are on a rack and a shaft "forcibly synchronized". Another possibility is a length-adjustable crossbar with which the hoists are "stiff in height" get connected.

In hydraulic hoists with two lifting cylinders is from the DE 35 15 762 discloses a so-called donor / slave system. The Lift cylinders are designed so that the volume in the bar space one cylinder the volume of the piston chamber in the second cylinder equivalent. With this arrangement, the movements the piston rods of the two lifting cylinders are hydraulically synchronized. An independent process of the piston rods of the two However, lifting cylinders are no longer possible.

The object of the present invention is a control device to create lifts that are easy and accurate to grasp and control of the lift height of the lift.

This problem is solved by the independent claim. The dependent claims relate to advantageous developments the invention.

The control device according to the invention has at least one ultrasonic transmitter for emitting ultrasonic waves and at least an ultrasound receiver. An evaluation device determines the lifting height h der based on the signals from the transmitter and receiver Lift. An ultrasonic displacement measurement to determine the lifting height h is contactless, maintenance-free, suitable for larger lifting heights, insensitive to contamination and inexpensive. The ultrasonic path measurement enables a precise determination of the Lifting height h. In contrast to an optical or magnetic scanning system effort and costs are independent of the travel or Scan path.

The control device can have at least one adjusting device for raising or lowering the lifting platform and a control unit for controlling the adjusting device on the basis of the determined lifting height h. Such a control device enables precise setting of the desired lifting height H ₀ over a wide range from a few centimeters to several meters.

The control device according to the invention can be used, for example, for activation of motor vehicle lifts, height-adjustable work platforms, especially for performing work on Buildings, and mobile height-adjustable work equipment, in particular used for transporting containers or the like become. Due to the very precise determination of the lifting height by means of the ultrasonic measurement, the control device can be precise Setting the height of a platform for loading and unloading Vehicles, ships or aircraft are used.

In order to set the lifting platform to the desired target height H ₀ , it is expedient for the control unit to compare the determined lifting height h with the predetermined target height H ₀ and to control the adjusting device of the lifting platform as a function of the comparison result. For this purpose, the control unit can have a controller known per se with a predetermined control characteristic and / or a power amplifier for controlling the adjusting device or a hydraulic unit which generates a fluid pressure for operating the adjusting device.

The transmitter can emit ultrasound pulses of a predetermined length of time send out and the evaluation device a sound propagation time T of the ultrasonic pulses determine from sender to receiver. Through the Measurement of the time it takes a sound wave to travel from the transmitter to the The evaluation device can take the receiver into account the speed of sound c the distance covered Determine sound wave. Due to the known arrangement of The transmitter and receiver can use the evaluation device the lifting height h the lift. Because the signal energy of an ultrasonic pulse The length of the ultrasound pulse depends on the duration of the pulse to be chosen so that a sufficiently reliable detection the pulse is guaranteed by the receiver.

To determine the sound propagation time, it is therefore advisable if the transmitter emits an ultrasound pulse (burst) of a certain length, e.g. 1 ms, sends out. The receiver detects the emitted ultrasound pulse, after covering the distance from sender to receiver Has. The evaluation device can the time delay T between sending and receiving the ultrasound pulse by, for example, an electronic circuit with one of the Determine transmitter signal S triggered counter. The counter counts the Counts of a clock until the received signal E the threshold of a Schmitt trigger. This runtime measurement can be repeated periodically, for example every 10 or 100 ms.

The ultrasonic transmitter can advantageously use digital control signals controlled to send digital ultrasound signals become. The evaluation device can be continuously distinguished generate digital code words in the form of pulse trains from the transmitter be sent. The individual code words can be random or can be generated according to a specified scheme. It is special advantageous to generate optimally discriminatory code words that for example a maximum (inhibitory) distance from a code word to the next code word or which are orthogonal to each other are. The digital code words change from sender to receiver transmitted and arrive there with a time delay T.

The evaluation device can expediently be a correlation device which have the time delay T between the Sending a code word and receiving the code word determined. For this purpose, the correlation device can be a digital correlator have, which determines the correspondence of binary signals. This is preferably done by moving one of the two signals in a shift register and the detection of the signal match. By the maximum of this digital cross-correlation function between sent code word and received Signal can have the signal runtime with a temporal resolution of one Clock period can be determined. For example, at a transmitter frequency of 40 kHz, a path resolution of 8.25 mm can be achieved. By evaluating the digital signal correlation, the Runtime measurement insensitive to interference. Individual bit errors in signal transmission reduce the signal match between transmitted and received signal and reduce the Absolute value of the maximum of the correlation function. The location of the However, the maximum can be determined further. By a suitable one Selection of the successive code words can also do this in the event of several bit errors, still reliably from the correlation device can be detected. By measuring the transit time using digital transmit signals can continuously determine the signal delay T from sender to receiver and a corresponding ongoing determination the lifting height of the lift.

The code length is expediently chosen so that a detection is guaranteed with sufficient security. Longer code words have the advantage that due to the larger number of bits are easier to discriminate and a larger signal Have energy, which increases the detection reliability of the receiver can be increased.

A phase evaluation device can expediently be located in the evaluation device to determine the phase relationship between the transmitter signal S and the receiver signal E may be provided. This can be done, for example, by measuring the time between one Edge of the transmitter signal S and an edge of the receiver signal E. happen. By detecting a change in this phase relationship can change the distance between transmitter and receiver be determined. To record the relative movement between The phase evaluation device compares the transmitter and receiver the excitation signal S of the transmitter with that detected by the receiver Signal E and determines the phase relationship between them generally periodic signals. The evaluation of the phase relationship has the advantage that transmitter and receiver are in one steady-state operation can be, causing swelling and decay the vibrations of the transmitter and receiver at the beginning and end of a pulse can be prevented and the measurement accuracy increases. The maximum resolution of the distance measurement is essentially by the accuracy of the phase evaluation, i.e. determined by a time measurement. Because time measurements with very high Accuracies are possible, the lifting height h can also be precise be determined

According to the invention, it is also possible to determine the amplitude of the emitted Modulate sound waves and the sound propagation time as well as the phase relationship to use for distance measurement. By amplitude modulation can, similar to the transmission of ultrasound pulses, the absolute sound propagation time T from the transmitter to the receiver is determined become. This can be done, for example, by evaluating the cross-correlation function between the transmitter signal S and the receiver signal E done. From the maximum of the cross correlation function can determine the time delay between these two signals become.

Furthermore, the sound propagation time can be determined by a digital one Send pulse train with the evaluation of the phase relationship between Transmitter signal S and receiver signal E can be combined. Through the Combination of absolute and incremental path measurement can the advantages of both methods can be used. The absolute distance measurement allows the distance between transmitter at any time and determine the receiver, regardless of any malfunctions, which, for example, the sound propagation between transmitter and Interfering with the recipient at short notice. To get the maximum resolution of the absolute displacement measurement by the wavelength of the ultrasonic waves or the time it takes to send an ultrasonic pulse or a digital transmission pulse sequence is required, is determined, can also increase the phase relationship between transmitter signal S and receiver signal E are evaluated.

For measuring the time between the rising edge of the transmitter signal S and the rising edge of the receiver signal E have the phase evaluation device expediently a gate circuit on the opens on a rising edge of the transmitter signal S and on a rising edge of the receiver signal E closes. It is beneficial the signals of the transmitter and the receiver beforehand via comparators (Schmitt trigger) to convert into square wave signals. Such one Gate switching can, for example, by means of appropriate logic gates and a flip-flop can be realized. Instead of the rising flanks the phase can also be evaluated on falling edges. at When the gate opens, the counting pulses of a clock generator reach one Counter that counts the incoming counts. The phase relationship between transmission signal S and receiver signal E results from the counter reading Z of the counter and the clock rate TR of the clock generator. The temporal resolution of the phase evaluation device can from the ratio of the clock rate TR of the clock generator to the transmission frequency f of the transmitter can be determined. This ratio determines TR / f also the maximum meter reading, i.e. the counter reading of the with a phase relationship of 360 ° between the signals S and E. occurs.

The counter can up to a predetermined number of counts N count and at the next incoming count pulse to a specific one Value to be reset. It is particularly beneficial if the counter at the by the ratio of clock rate to transmitter frequency TR / f certain number of counts reset becomes. The counter can for example up to this number N incoming Add pulses and reset to zero on the next pulse or starts at N counts and subtracts incoming pulses until the counter reading Z reaches zero.

Since the phase relationship between the signals S and E changes when the distance between the transmitter and receiver changes, the evaluation device can determine the lifting height h on the basis of the counter reading Z and the number R of resets of the counter. With an increase in the distance between the transmitter and the receiver, the phase shift between S and E and thus the counter reading Z increases until there is a phase jump when there is a change in distance of a wavelength λ of the transmitter signal. This phase jump is detected by the phase evaluation device on the basis of the reset signal R of the counter. The distance a between the transmitter and receiver results from the number of phase jumps R that occurred during the movement of the transmitter or receiver, multiplied by the wavelength λ, of the ultrasound signal. The ratio of the counter reading Z to the maximum number of counting pulses N multiplied by the wavelength λ is added to this value. The following applies to the distance: a = R · λ + Z N · Λ.

The measurement accuracy of this phase evaluation is λ N and can be easily adapted to the given requirements for the measuring accuracy of the lifting height h by appropriate selection of N.

Since the speed of sound c depends on the air temperature, is it is advantageous to use a sound velocity determination device provided. The speed of sound can be determined on the basis of the determined temperature t c, the sound propagation time T, the phase relationship between the signals S and E and / or the lifting height h determined or corrected become. This is particularly useful if there are different Parts of the lift other temperature conditions occur, e.g. by sun exposure or blown hot air a heater.

The control device can provide at least one temperature sensor, which is the air temperature t in the vicinity of the ultrasonic measuring section detected. To different temperatures in several positions of the lift, it is advisable to use several temperature sensors provided. The speed of sound c can, for example based on a temperature characteristic with a linear Connection or a root connection between Temperature t and speed of sound c can be determined. Based on this temperature compensation, the measurement accuracy the ultrasonic displacement measurement can be increased.

May be c for determining the speed of sound, a second receiver at a predetermined distance d provided by the transmitter The Amswertevorrichtung can on the basis of sound propagation time T _d to the second receiver and / or the phase relationship between the transmitter signal S and the signal of the second receiver c determine the speed of sound and / or correct the lifting height h. The following applies to the speed of sound: c = d T d ,

Since the speed of sound c is determined directly, potentials have Sources of error, e.g. the temperature, air pressure, humidity, no influence on the distance measurement and there is a higher measuring accuracy achieved.

The direction of propagation of the sound waves emitted by the transmitter to influence, it is advantageous to provide a focusing device. Since conventional ultrasound transmitters have a cardioid radiation pattern have, sound signals are also not direct Away from the sender to the receiver. Sound signals can, for example from a building wall or part of the lift be reflected and then reach the recipient with a longer one Sound path. Depending on the phase position of the direct Sounds to the reflected sound at the receiver can be added or subtraction of the signals interference that occurs Can affect distance measurement. By one attached to the transmitter Sound horn can affect the radiation characteristics of the transmitter be influenced and the sound waves are bundled. The biggest Part of the radiated sound energy can be directed to the direct sound path be concentrated between sender and receiver. Meßsignalverfälschungen through reflections or interference are reduced.

The receiver can be used to select incoming sound waves a corresponding device, in particular an aperture or a Tube. Because this selection device is preferred Transmits sound waves of a predetermined direction of propagation it is possible to suppress sound waves from other directions of propagation or suppress. The selection device is preferred the receiver is aimed at the direct connection to the transmitter, to dampen reflected sound waves.

Preferably, a reflector for reflecting that from the transmitter emitted sound waves may be provided. This is particularly advantageous if the measurement of the lifting height h by the reflection principle he follows. For this purpose, the transmitter and receiver are on one moving part the lift or arranged together stationary on the lift. For example, the sender and receiver are on the bottom the platform's height-adjustable platform. The transmitter emits ultrasonic signals towards the ground on which the Lift is arranged from. There are the emitted ultrasound signals from a reflector, for example one in the ground embedded metal plate, reflected. With the reflection principle results the lifting height h is half the distance a, which is the ultrasonic signal from sender to receiver. If that's the Object reflecting sound waves (e.g. the platform of the lift) has sufficient sound hardness and sufficient The proportion of the incident sound waves reflected is the attachment a separate reflector is not required.

The transmitter and receiver can be used as a combined ultrasound transducer be trained. The converter is used, for example, with a burst excited of 1 ms length. Then the converter is on reception switched. The reflected signal corresponds to the lifting height received by the converter with a delay. After stimulation by the Transmit burst, however, a certain waiting time must be observed, before the transmission signal has subsided and the converter as Receiver can be used. This results in a minimal Path length that the signal from the transmitter to the receiver or from Transducer to the reflector and back must travel.

To avoid this minimal path length, transmitters and Receiver designed as separate transmitting and receiving units his. These should preferably be arranged so that between the transmitter and receiver no structure-borne noise coupling occurs. For distance measurement According to the principle of reflection, the sending and receiving unit for example, be arranged side by side. However, it is also possible for direct path measurement of the transmitter and receiver without operating a reflection of the sound waves. Send- and the receiving unit are at the two ends of the measuring distance arranged.

The transmitter can, for example, be stationary on the lifting platform or the Floor or the foundation on which the lift is placed his. By arranging the receiver on a movable Part of the lift can be the distance a between the transmitter and receiver be determined. For example, if the recipient is on a height-adjustable platform of the lifting platform or a supporting structure arranged to raise the load, the distance a between Transmitter and receiver essentially the lifting height h Lift. Should the receiver not be directly on the part of the lift attached, the lifting height h of which can be determined, can this by evaluating the geometric relationships (lever arms, Angles, ratios, etc.) between the parts of the lift become. A reverse arrangement is of course also possible of sender and receiver possible.

Transmitter and receiver can be adjusted on the lift be arranged around a travel path v of the adjusting device to determine. The evaluation device determines the lifting height h based on the travel path v and the geometric relationships (lever arms) the lift. An arrangement of transmitter and receiver on the adjustment device is structurally simple and has the Advantage that the measuring section between transmitter and receiver against an accidental interruption of sound propagation largely is protected.

The adjusting device can preferably be a hydraulic cylinder or a pressurized cylinder. In this The transmitter or receiver can fall on the one hand on the cylinder housing and on the other hand on the movable piston rod or one be arranged with this connected component. Of course are other adjustment devices, e.g. on Spindle drive, possible.

It is also possible to provide several adjustment devices are. The evaluation device expediently determines on the basis of of the respective travel paths v of the adjustment devices, the lifting height h the lift. Depending on the arrangement of the adjustment devices to consider their travels v accordingly. For example are the travel paths in a series connection of the adjustment devices to add v.

To increase the measuring accuracy and / or the lifting height of the lift Multiple transmitters can determine at multiple locations and receiver can be provided. The evaluation device detects the corresponding sound paths between the respective transmitters and Receiver and determines the lifting height h of the lift.

The evaluation device preferably determines the lifting heights h _a , h _b of different parts of the lifting platform, in particular of a plurality of lifting platforms, lifting arms or cantilevers of the lifting platform. This is particularly expedient if the lifting platform is constructed in several parts and the individual parts have their own adjustment devices. For example, lifting platforms for motor vehicles can have separate platforms or driving surfaces for the left and right wheels of the vehicle. These separate driving surfaces are usually moved by separate hydraulic cylinders.

In order to achieve a uniform movement of the individual parts of a multi-part lifting platform, it is advantageous if the control unit controls the adjustment devices. In particular, the control path v and / or the speed of the adjustment movement can be synchronized by the control. For this purpose, the control unit can compare the lifting heights h _a , h _b determined by the evaluation device and / or their changes over time and determine deviations. If deviations are found, the control unit can, for example, briefly stop a leading adjustment device and / or influence its adjustment speed. This can be done by a corresponding control of a hydraulic unit for generating hydraulic pressure for the adjusting devices and / or an actuation of hydraulic valves. The control unit preferably controls the adjustment devices, the hydraulic unit and / or the valves in order to achieve a uniform height h of the platform or uniform lifting heights h _a , h _{b of} the platforms of multi-part lifting platforms. The lift can be positioned very precisely due to the precise ultrasonic displacement measurement and the possible precise control of the lifting height or lifting heights. This is particularly important when carrying out measurements on the object standing on the lift or raised by it. The control device according to the invention allows, for example, multi-part driving surfaces of motor vehicle lifts to be positioned so precisely that wheel alignment on vehicles is possible.

When a predetermined lifting height H _{0 of} the lifting platform is reached, the control unit can also carry out a predetermined control function. For example, warning signals and / or lighting can be switched on and off by the control unit. When the predetermined lifting height H _{0 is reached} , the control unit can also automatically start a measurement or test program.

Fig. 1 schematisch ein Ausführungsbeispiel der erfindungsgemäßen Steuervorrichtung;

Fig. 2 eine schematische Darstellung zur Erläuterung eines Ausführungsbeispiels einer Auswertevorrichtung;

Fig. 3 eine schematische Darstellung zur Erläuterung eines Ausführungsbeispiels einer Steuereinheit;

Fig. 4a zeigt schematisch ein weiteres Ausführungsbeispiel für eine erfindungsgemäße Anordnung zur Wegmessung; und

Fig. 4b zeigt schematisch die Signale A, B, C, D der Messanordnung nach Fig. 4a.

Preferred exemplary embodiments of the invention are explained below with reference to the drawing. Show it:

Fig. 1 shows schematically an embodiment of the control device according to the invention;

2 shows a schematic illustration to explain an exemplary embodiment of an evaluation device;

3 shows a schematic illustration to explain an exemplary embodiment of a control unit;

4a schematically shows a further exemplary embodiment for an arrangement according to the invention for displacement measurement; and

4b shows schematically the signals A, B, C, D of the measuring arrangement according to FIG. 4a.

Fig. 1 shows schematically an embodiment of the invention Control device for lifting platforms. The control device has an ultrasound transmitter 1 for emitting ultrasound signals, e.g. with a frequency of 40 kHz. The ultrasonic transmitter 1 sends ultrasonic pulses, e.g. with a length of 1 ms. The This ultrasonic pulse is emitted by an evaluation device 3 controlled and monitored.

In order to influence the direction of propagation of the emitted sound waves, the transmitter 1 has a sound horn 13. The Schallhorn 13 bundles the emitted sound waves in a preferred direction of radiation, to reduce unwanted reflections of the sound waves.

The sound waves emitted by the transmitter 1 meet a movable one Part of the lift 10 and are reflected there. Because in the shown Embodiment the sound waves on the underside of a height-adjustable Platform 16 of the lift 10 hit and the Reflection coefficient of the platform 16 sufficient reflection of the No additional reflector is provided for sound waves.

The reflected sound waves are from an ultrasound receiver 2, which is connected to the evaluation device 3, detected. Channel In this example, 1 and receiver 2 are separate transmitters Receiving units designed to a structure-borne noise coupling to prevent and send and receive the sound waves without waiting time when switching from transmit to receive mode enable. Since the receiver 2 is not due to the decay of the transmission signal must wait in transmitter 1, there is no minimum signal runtime for to comply with the sound waves.

The transmission of the ultrasound pulses from the transmitter 1 is initiated by the evaluation device 3 at predetermined intervals. The evaluation device 3 determines the signal propagation time T of the ultrasound pulses from the transmitter 1 to the platform 16 and back to the receiver 2. The lifting height h of the lifting platform results as half of the path covered by the sound waves. This is determined by evaluation device 3 from sound propagation time T and sound speed c: h = c T 2 ,

In order to take into account the influence of the air temperature on the speed of sound c, a second receiver 11 is provided at a predetermined fixed distance d from the transmitter 1. The evaluation device 3 determines the sound propagation time T _d from the transmitter 1 to the second receiver 11 and determines the speed of sound: c = d T d ,

The lifting height h determined by the evaluation device is fed to a control unit 4. This compares the determined lifting height h with a predetermined target height Ho and controls the adjusting device 5, here a hydraulic cylinder, in such a way that the target lifting height H _{0 of} the lifting platform 10 is reached.

Depending on the determined lifting height h, the control unit 4 can also carry out further control functions, such as, for example, switching warning tones and / or lights on and off. Evaluation device 3 and control unit 4 are preferably designed as an electronic unit, for example a microcontroller or a programmable control unit. The target height H ₀ can be entered manually, for example using a keyboard or another input device. It is also possible for the target height H _{0 to be} specified by a measuring or control computer.

2 shows a schematic illustration to explain a Evaluation device 3 according to the invention.

In the embodiment shown, the transmitter 1 is on the movable Cylinder rod 23 of a hydraulic cylinder 5 is arranged. The Receiver 2 is located on the cylinder housing 24 of the hydraulic cylinder 5. The evaluation device 3 determines the phase relationship the travel distance between transmitter signal S and receiver signal E. v of the hydraulic cylinder 5. Due to the known geometric Arrangement of the lifting platform 10 can be based on the Travel v the lifting height h of the lifting platform 10 can be calculated.

The evaluation device 3 has a phase evaluation device 8 on which the phase relationship between the transmitter signal S and the receiver signal E determined. The signals E and S are over two comparators (Schmitt trigger) 19 converted into square wave signals. The phase evaluation device 8 measures the time between the rising edge of the transmitter signal S and the rising edge of the receiver signal E. A gate circuit 6 is provided for this purpose, which opens with a rising edge of the signal S and with a rising edge of signal E closes. With the gate open Count pulses from a clock 7 added in a counter 12. additionally the counter reading is at an edge of the transmitter signal S. the previous measurement.

With a sound transmission frequency of 40 kHz and a clock rate of 16 MHz, there is a maximum counter reading N = 400 with a phase shift of 360 ° or 2π. The maximum phase shift between the signals S and E corresponds to the period of the transmission signal S or the reciprocal of the excitation frequency f. The maximum time between the edge of the transmitter and that of the receiver is 25 ms at f = 40 kHz. The time resolution of the phase evaluation device 8 is thus 1 N. f ·

If the lifting platform 10 is moved, i.e. Move transmitter and receiver relative to each other, the phase relationship between changes Transmitter signal S and receiver signal E. Moving transmitter and receiver apart for example, the phase shift and the value Z of the counter increases until it reaches the maximum number of counting pulses N reached. After reaching N the Counter again with zero. When the lift is lowered, the counter reading Z correspondingly smaller to zero when the value is reached to jump back to N. At a speed of sound of 340 m / s and an excitation frequency of 40 kHz is reset of the counter after changing the sound path by 8.5 mm.

To determine the lifting height h, the number of jumps or Counter resets R detected when moving the lift 10 become.

The path resolution that can be achieved by evaluating the phase relationship in the example mentioned above with N = 400 is 0.02 mm.

In order to compensate for the influence of air temperature t on the speed of sound, a speed of sound determination device 12 and a temperature sensor 9 are provided. The temperature sensor 9 is preferably arranged in the vicinity of the measuring section between transmitter 1 and receiver 2 and measures the air temperature t there. The speed of sound determination device 12 determines the speed of sound c on the basis of a temperature characteristic:

Through the temperature compensation of the speed of sound c the lift height h can be set precisely. Are several Adjustment devices for lifting or lowering the lift provided, the temperature influences on the individual Adjustment devices are corrected, which results in synchronous lifting and lowering also possible at different temperatures is. For example, part of the lift can be in a climatic chamber be arranged. Another part of the lift is e.g. illuminated by the sun or blown by a heater To avoid interference and interference from reflected sound signals suppress, a tube 14 is attached to the receiver 2. By the tube 14 is achieved that preferably sound waves with a Direction of propagation in the axial pipe direction reach the receiver 2 can. Reflected sound signals with different directions of propagation are suppressed. It is also possible for the recipient 2 to move in the tube 14 together with the lifting platform 10, the transmitter 1 the tube 14 at a predetermined distance, e.g. 10 cm, illuminates. This way only the sound waves get in the measuring tube, which is essentially the direct path between the transmitter 1 and receiver 2 correspond. The receiver signal E is essential more stable because modulation with reflected sound is reduced becomes.

3 shows a schematic illustration to explain a Control unit according to the invention 4. The two-part lifting platform 10 has two platforms 16a, 16b. There is a combined ultrasound transducer on each of the two platforms 16a, 16b 17a, 17b provided. Are in the ground or foundation Reflectors 15a, 15b attached by the ultrasonic transducers 17a, 17b reflect emitted sound waves.

The evaluation device 3 determines the heights h _a , h _{b of} the two platforms 16a, 16b of the lifting platform 10. These lifting heights h _a , h _b are fed to a control unit 4. To control the lifting heights h _a , h _b , the control unit 4 forms the control deviations h _a - H ₀ , h _b - H ₀ and, if appropriate, h _a - h _b . These differences are evaluated by a control device 20 in order to control the lifting heights h _a , h _{b of} the platforms 16a, 16b synchronously. Power elements 21a, 21b control a hydraulic unit 22 for generating the respective hydraulic pressure for the adjusting devices 5a, 5b. The control device 20 can carry out a height control and / or a speed control of the adjustment devices 5a, 5b. In this way it is possible to raise or lower the platforms 16a, 16b synchronously.

Furthermore, proportional or binary switching actuators, e.g. Hydraulic valves can be provided to perform the control functions. The actuators can by the control device 20 or the power elements 21a, 21b are actuated and the pressure in affect the hydraulic cylinders 5a, 5b. Since in this case the The hydraulic cylinders 5a, 5b are controlled via the actuators, it is possible to provide a simpler hydraulic unit 22 which creates a constant pressure.

4a schematically shows a further embodiment for an inventive arrangement for determining the lifting height h. A signal generator 25 generates square-wave signals A (e.g. at 40 kHz) that via an electronic controlled by the evaluation device 3 Switch 26 and a signal amplifier 27 to the ultrasound transmitter 1 are fed. The signal to control the switch 26 is denoted by B and the signal fed to the transmitter denoted by C. By the switch 26, the continuous wave signal A is cyclically switched on and off. The receiver 2 receives the ultrasound signal and conducts it the received signal D via a signal amplifier 28 of the evaluation device 3 to. This leads to the determination of the distance between Transmitter 1 and receiver 2 using the signals A shown in FIG. 4b, B, D through. With appropriate arrangement of transmitter 1 and receiver 2 this distance corresponds to the lifting height h of the lift.

It is advisable to increase the operational safety of the lift both an incremental and an absolute distance measurement perform. The incremental distance measurement takes place after the principle of phase evaluation between transmit and Reception signal. This measurement can be done with high accuracy and provides an exact indication of the travel path of the lift. However, the sound path between transmitter 1 and receiver 2 interrupted, the evaluation device 3 can synchronize lose between transmit and receive signal and count pulses can be lost. Usually the lift is an emergency stop and a manual return of the lift to a reference position required.

In order to make the control device more robust against such problems, a combined evaluation of the phase relationship p between transmission and reception signal C, D and the sound propagation time T between transmitter 1 and receiver 2. Since it is in the investigation the sound propagation time T by an absolute distance measurement it can be used again and again and regardless of previous measurements be performed. Should the (more precise) phase evaluation can be disturbed and fail, based on the runtime measurement the (approximate) lift height of the lift is still determined become. The redundancy of the measurements thus increases operational safety the lift increased. The lower accuracy of the runtime measurement in the order of the wavelength used (e.g. λ = 8.5mm) can be accepted. The measurement accuracy can also be increased by triggering on the positive and negative edge of the incoming pulse in the received signal D. In this way, a resolution the distance measurement of λ / 2 can be achieved. This is for an emergency operation and some uses of the lift are sufficient.

The double distance measurement can be carried out cyclically, as in Fig. 4a, b shown. The continuous wave signal A is periodically by the Switch 26 modulated. Based on the received signal D is then both the transit time T and the phase relationship p are determined and evaluated.

The runtime measurement is preferably carried out at times when the Lift is not moved. Then the continuous wave operation can be interrupted without disturbing the phase evaluation. For example when the control device receives a drive command that Sound propagation time in pulse mode determined before the lift moves and the transmitter for phase evaluation on continuous wave operation is set. In this way, a control value can be set before starting for the lifting height h determined by the absolute displacement measurement become. This control value can be compared with a constant, Non-volatile memory stored actual value for the lift control be compared to determine if the altitude measurement was carried out without errors. Such an approach enables an additional control of the lift position and thus increases operational safety.

However, it is also possible to measure only in normal operation Support phase evaluation and only in the event of a fault on one Toggle transit time measurement. In normal operation there is a continuous wave signal sent and in the event of a fault on a pulse operation of transmitter 1 switched. A fault can be caused by an evaluation of the received signal D can be recognized. For example, the Received quality recorded and / or the absence (absence) of impulses be recognized. Also based on the shape of the received Signals can indicate a disturbance in the (ultrasound) transmission become.

Claims (27)

Control device for lifting platforms, with an ultrasonic transmitter (1), an ultrasound receiver (2), an evaluation device (3) based on the signals from the transmitter (1) and receiver (2) the lifting height h of the lifting platform (10) determined, at least one adjusting device (5) for raising or lowering the lifting platform (10) and a control unit (4), which the adjusting device (5) on the Controls based on the determined lifting height h. Control device according to claim 1, wherein the control unit (4) compares the determined lifting height h of the lifting platform (10) with a predetermined target height Ho and controls the adjusting device (5) such that the target height H _{0 of} the lifting platform (10) becomes. Control device according to claim 1 or 2, wherein the transmitter (1) Sends ultrasonic pulses and the evaluation device (3) a sound propagation time T of the ultrasonic pulses from the transmitter (1) to Determined receiver (2). Control device according to claim 1 or 2, wherein the transmitter (1) emits digital ultrasound signals and the evaluation device Determine transmitter (1) to receiver (2). Control device according to claim 4, wherein the correlation means a shift register for shifting the digital transmitter signal S or the digital receiver signal E. Control device according to one of claims 1 to 5, wherein the Evaluation device (3) a phase evaluation device (8) for Determination of the phase relationship between the transmitter signal S and the receiver signal E and a change in Distance between transmitter (1) and receiver (2) by detection a change in the phase relationship. Control device according to claim 6, wherein the phase evaluation device (8) a gate circuit (6), which with a rising Edge of the transmitter signal S opens and on a rising edge of the receiver signal E includes a clock (7) and one Has counter (12) which, when the gate circuit (6) is open Counts of the clock (7) counts. A control device according to claim 7, wherein the counter (12) is one predetermined number of counts N counts and at the next incoming count pulse reset to a certain value is, and the evaluation device (3) based on the lifting height h the counter reading Z and the number of counter resets R determined. Control device according to at least one of claims 1 to 8, the evaluation device being a sound velocity determination device (18), which is the speed c determines the sound waves emitted by the transmitter (1) in order to the sound propagation time T, the phase relationship and / or the lifting height h to determine or correct. Control device according to claim 9, comprising a temperature sensor (9) to determine the speed of sound c, in particular based on a temperature characteristic. Control device according to claim 9 or 10, which has a second receiver (11) arranged at a predetermined distance d from the transmitter (1), the evaluation device (3) based on the transit time T _{d of} the sound wave from the transmitter (1) to the second receiver (11) and / or the phase relationship between the transmitter signal S and the signal of the second receiver (11) determines the speed of sound c. Control device according to at least one of claims 1 to 11, wherein the transmitter (1) has a focusing device (13) for focusing of sound waves, in particular a sound horn. Control device according to at least one of claims 1 to 12, the receiver (2) having a device (14) for selection of incident sound waves, in particular an aperture or a tube, has the sound waves of a predetermined direction of propagation passes. Control device according to at least one of claims 1 to 13, which has a reflector (15) for reflecting the from the transmitter (1) emitted sound waves. Control device according to at least one of claims 1 to 14, transmitter (1) and receiver (2) as a combined ultrasound transducer (17) or as separate transmitting and receiving units are trained. Control device according to at least one of claims 1 to 15, the transmitter (1) fixed and the receiver (2) on one movable part of the lifting platform (10) is arranged, or the Transmitter (1) on a movable part of the lifting platform (10) and the receiver (2) is arranged stationary. Control device according to at least one of claims 1 to 16, the transmitter (1) and / or the receiver (2) on one height-adjustable platform (16) of the lifting platform (10) arranged are. Control device according to at least one of claims 1 to 16, the transmitter (1) and the receiver (2) on the adjusting device (5) are arranged, and the evaluation device (3) To determine the lifting height h, a travel path v of the adjustment device (5) determined. Control device according to at least one of claims 1 to 18, wherein the adjusting device (5) is a hydraulic cylinder. Control device according to at least one of claims 1 to 19, several adjustment devices (5) being provided, and the evaluation device (3) shows the respective travels v Adjustment devices (5) determined. Control device according to at least one of claims 1 to 20, several transmitters (1) and receivers (2) being provided are. Control device according to claim 21, wherein the evaluation device (3) determines the lifting heights h _a , h _b of different parts of the lifting platform (10), in particular of several lifting platforms (16a, 16b), lifting arms or cantilevers of the lifting platform (10). Control device according to at least one of claims 20 to 22, the control unit (4) regulating the adjustment devices (5) executes, in particular, the same travel path v and / or a speed synchronism of the adjustment devices (5) to achieve. Control device according to at least one of claims 20 to 22, wherein the control unit (4) carries out a regulation of the adjusting devices (5) in order to achieve a uniform height of the platform (16) or equal lifting heights h _a , h _{b of} the platforms (16a, 16b) to achieve. Control device according to at least one of claims 1 to 24, wherein the control unit (4) when reaching a predetermined Lifting height Ho of the lift (10) a predetermined control function performs. Control device according to at least one of claims 1 to 25, wherein the evaluation device (3) determines the lifting height h using the Measurement of the sound propagation time T and the evaluation of the phase relationship determined between transmitter signal S and receiver signal E. Lift, in particular for motor vehicles, with a control device according to at least one of claims 1 to 26.

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