EP0039003A1

EP0039003A1 - Electronic safety ski binding which automatically adjusts itself to the correct release value

Info

Publication number: EP0039003A1
Application number: EP81102904A
Authority: EP
Inventors: Walter Dr. Knabel; Hans Engstfeld; Nicholas Fred D'antonio
Original assignee: Marker Patentverwertungs GmbH
Current assignee: Marker Patentverwertungs GmbH
Priority date: 1980-04-24
Filing date: 1981-04-15
Publication date: 1981-11-04
Also published as: DE3167035D1; JPS5734878A; PL230781A1; JPH0134068B2; YU106781A; EP0039003B1

Abstract

A safety ski binding having force transducers, which derive analog electric signals from vertically acting forces occurring in the ball and heel portions of a skiing boot and from torques acting on the skiing boot. An electronic circuit or a microprocessor is provided having a converter for converting signals from the force transducer into a value which depends on the magnitude and duration of the signals and a comparator circuit for comparing the value with a threshold value which corresponds to permissible stresses. The comparator generates a signal for initiating release of the binding when the threshold value is exceeded. An electric circuit is provided for detecting those of the forces sensed by the force transducers which act in the same sense in a vertical direction during the time for which these forces are acting when no torques are being detected. This circuit detects forces, such as the weight of the skier, if the forces are quasistatic. Another circuit is provided which, in accordance with a predetermined program, sets the release value in dependence on the measured weight of a skier.

Description

This invention relates to a safety ski binding comprising force transducers, which derive analog electric signals from the vertically acting forces occurring in the ball and heel portions of the skiing boot and from the torques acting on the skiing boot, an electronic circuit or a microprocessor for converting said signals into a value which depends on the magnitude and duration of the signals, and a comparator circuit for comparing said value with a threshold value which corresponds to permissible stresses and for generating a signal for initiating the release of the binding when said threshold value is exceeded.
To ensure a satisfactory function of a safety ski binding, the latter must be adjusted to a release value which is specific for the individual skier. That release value depends significantly on the required retaining force, which must be smaller than the force which can be safely taken up by the skier's leg under a quasistatic load. That force can be determined on the basis of empirical values by a measurement of the diameter of the head of the tibia or, with sufficient accuracy, in dependence on the weight of the skier.
Modern safety ski bindings are so designed that a release will not always take place whenever the skier's leg is being subjected to forces in excess of the retaining force but the binding will not be released until such forces have acted for an excessively long time. The criterion for the release is the energy, or preferably the momentum, which can safely be taken up by the leg because stresses caused, for instance, by force surges and having force peaks which are greatly in excess of the retaining force need not result in a release.
Most skiing accidents are due to ski bindings which are not properly adjusted either because they have been maladjusted when they were purchased or because they have not been adequately serviced, e.g., when they are used in a new season without a previous check.
For this reason it is an object of the invention to provide an electronic safety ski binding which is always set to the release value which is proper for the skier regardless of a pre-adjustment of the binding.
In a safety ski binding of the kind stated first hereinbefore this object is accomplished according to the invention in that an electric circuit is provided, which detects thos= of the forces sensed by the force transducers which act in the same sense in a vertical direction during the time for which these forces are acting when no torques are being detected and said circuit detects said forces as the weight of the skier if said forces are quasistatic, and that another circuit is provided which in accordance with a predetermined program sets the release value in dependence on the measured weight of the skier. The safety ski binding according to the invention senses the weight of the skien when the same stands approximately symmetrically between the front and rear force transducers, so that the same are loaded in the same sense, and the weight is applied to these force transducers for a relatively long time, whichJs typical of substantially static loads, so that dynamic loads which may be due to vertical accelerations cannot result in a wrong weight measurement. Another criterion for a correct weight measurement resides in the absence of torsion, which would suggest that the skier does not apply substantially static loads to the force transducers. A3 a rule, it can be assumed that the weight of the skier is approximately equally distributed to the front and rear force transducers during the quasistatic weight measurement. Alternatively, the weight measurement may be effected in such a manner that the sum of the forces measured by the front and rear force transducers is formed so that unequal loads applied to the front and rear force transducers are not detected as a torque.
To eliminate force peaks which cannot be regarded as a weight, the measurement is taken for a substantial time and only forces which do not suddenly change during that time are regarded as forces due to a weight.
The weight measured by a force pick-up can be converted into digital signals by an analog-to-digital converter. That conversion is effected within a predetermined time in accordance with the predetermined time constant. In that conversion, the digital signals which are analogous to the measured weight are processed only when the measurement does not indicate sudden fluctuations during that time, which is predetermined by the time constant.
The safety ski binding according to the invention will automatically adjust itself to a higher threshold value when the force transducers sense a higher quasistatically acting force which is due to a weight. The threshold value which corresponds to the highest release value will be reached when the skier is standing on one leg and with its weight is applying a quasistatic load only to one binding.
The first adjustment of the threshold value is effected as the skier is stepping into the binding, or immediately thereafter, when the load due to the weight of the skier is initially applied to the binding.
Dynamic loads which would result in a wrong setting will be eliminated because loads applied only for a short time are not detected as weight loads.
A former threshold value is replaced by a new one whenever the quasistatic weight measurement indicated a higher weight, which results in a correction of the former, lower threshold value. An increase in weight which results in an increase of the threshold value may be due to the fact that the skier may be loading both legs more uniformly during the stepping and starting phases so that the entire weight of the skier does not rest on one leg and the binding is not yet set to the highest release value.
In addition to the weight of the skier, his ability is another criterion for the required release value. The controlling forces which may be exerted by a highly skilled skier, such as a racer, during skiing, may exceed the release values which have been computed from the weight of the skier. On the other hand, the controlling forces exerted by a less highly skilled skier may be lower than the release value J which corresponds to the skier's weight. For this reason it will be desirable to set the ski binding to a release value which is higher or lower than the weight of the skier, in dependence on his skiing ability.
For this reason, a further development of the invention calls for a circuit in which torques between the range of torques which are due to force surges exerted during skiing and the range of torques acting for such a magnitude and time as to be dangerous to the leg, are detected as torques which are due to controlling forces and in said circuit the threshold value is set in accordance with a predetermined program to a value which is higher or lower than the threshold value that is due to the weight.
Different from a static load due to a weight, controlling forces result in torques which are transmitted from the skiing boot to the ski. These torques may be generated in a horizontal direction, in a vertical direction and in a diagonal direction. A distinction must be made between short-time torques, which may be due to force surges rather than to controlling forces, and long-time torques, which are no longer controlling forces but quasistatic torsional forces, which may result in leg fracture. In accordance with the invention, only the torques in the range between the harmless force surges occurring during skiing and the torques acting for a dangerously long time are detected as controlling forces which influence the threshold value for the release.
Owing to the adjustment of the threshold value for the release in dependence on the controlling forces, the safety binding according to the invention will be set in dependence on the ability and technique of the respective skier.
For instance, if the skier during skiing requires only controlling forces which are below the release threshold value corresponding to his weight, then the threshold value may be lowered so that an unnecessary release need not be feared although the binding is set to a value which is below the value which corresponds to the weight of the skier.
According to a further development of the invention, the threshold value is not changed in response to those torques which are near the respective threshold value and are detected as torques which are due to controlling forces. If torques approaching the presently set threshold value are detected as controlling forces, such torques will not cause the binding to be set to an excessively high threshold value but as extreme values will not be recorded.
According to a further development of the invention, the forces measured by the force transducers are summed or integrated in dependence on the gradient of the force increase with time to compute the release value which is to be compared with the threshold value. In that case, quickly increasing forces are integrated less rapidly than slowly increasing forces. A reliable release of a binding depends not only on the threshold value but also on the time which expires until the threshold value is reached or exceeded. A skier skiing on a hard slope will be subjected to high-frequency force surges having a relatively large amplitude. Because these low-energy force surges, which are harmless, should not be integrated to result in a release, the interval of time during which there is an integration to the release value can be increased. In the opposite case, when there are force surges which have a smaller amplitude and are possibly at a lower frequency, the release value should be reached sooner because these force surges have usually a higher energy so that they are more dangerous. For this reason, such force surges should be integrated more rapidly to the release value.
The criterion for the dangerousness of the force surges is the gradient of the force increase, i.e., the rate of increase of the measured force. A force increase at a high rate will indicate short force surges, which are of a harmless kind and should not result in a release. On the other hand, stresses involving a more gradual force increase should be integrated more quickly to the release value.
The operation of the inventive ski-binding is based on an automatic determination of skier weight when certain preselected requirements are satisfied, in particular:

1. Both forward and rearward modules for F_z are detecting a downward force, i.e. weight, and therefore no M_y moment as defined in the accepted convention of figure 4,
2. no significant signals on either of the modules F ,
3. the conditions of 1. and 2. remain in a stable state for the preselected period of time, perhaps from 1 to 3 seconds,
4. the weight signal is stored if, and only if, the new value is greater than the present value.

Weight detection can occur at any time, but preferably when the skier first begins; however, if for some reason the TAKE WEIGHT condition is not satisfied, the system will use a preselected minimum initial threshold for the processor to work with. Since the transducer response is linear, the weight is accurately determined by taking the sum of the front and rear modules for F_z, so long as both are stressed in the downward direction.
Regardless of the origin of the threshold of release, as soon as the skier begins to generate steering signals in either the M y or M_z moments, a perpetual modification to the release threshold will occur, the direction and magnitude of the changes being determined by the strength and time characteristics of the steering signals. The "Steering Window" consists of three important threshold levels, all of which originate from the resident threshold of release (THDREL); they are:

1. LOLIM (Low Limit)

Signals below this value are considered to be of no interest and therefore no modification is made to the threshold.

2. MEDIAN

This second level decides if the instant steering signal will cause an increase or decrease in the threshold. Signals that are greater than LOLIM but smaller than MEDIAN are considered to be "weak" and therefore the threshold of release is reduced in magnitude. Signals that are greater than MEDIAN but smaller than UPERLIM (Upper Limit) are considered "strong" signals and will cause the threshold to increase.

3. UPERLIM (Upper Limit)

When a steering signal is greater than UPERLIM, no modification is made to the threshold.
Regardless of the strength of the steering signal, no modification to the threshold is made until the signal falls below the LOLIM level; this is done to make sure that the correct signal magnitude is used by the processor.
A preferred embodiment is described in the drawings in which show:

Figure 1: System Block Diagram,
Figure 2: Schematic diagram of one possible embodiment of system,
Figure 3: Graphical representation of system operation.
Figure 4: Axial representation of a ski boot showing the direction of the forces and moments.

Figure 1 and Figure 2:

In each of the diagrams, the functional blocks are numbered for easy identification. Figure 1 is used to describe the purpose of the function and its relationship to the other networks in the system. The details of their operation for this particular embodiment are then given in the description of Figure 2.
Block 1 The "System Clock" and associated decoding networks provide all of the basic timing requirements for processor operation and assures that everything happens at the correct time and in the correct order. It also provides the measurement of time as needed to satisfy the delay for a valid "TAKE WEIGHT" interval. A timing signal is shown going to the "Weight Detection Network" (Box 4) for this purpose. In Figure 2, this function is shown as an oscillator, a digital counter to provide the delay and a monostable (M 1) to produce a single pulse when the delay has been satisfied.
Block 2 The F_z transducers (forward and rearward F modules) will generate a voltage when a downward force appears, and a voltage of the opposite polarity when an upward force appears. Consequently, when an M_y moment occurs, depending on the direction, the front and rear modules will have the opposite polarity, however, if a "Weight" situation exists, both front and rear modules will have the same polarity. When this happens, weight detection (Box 4) will know a "TAKEWT" interval may be on the way. In Figure 2, this function consists of the "Rear F_z" and "Forward F_z" networks, their respective amplifiers (A 1 & A 2) to increase the F_z signals to usable levels and a differential amplifier (A 3) to provide the "moment" signal M_y resulting from the front and rear modules having opposite polarities.
Block 3 The F_y modules also provide the "moment" M_z for normal skiing signals, however, during a valid "TAKEWT" interval, the system demands that the M_z signals be close to zero. Thus, the F_y input to the weight detection network (Box 4) assures this condition. In Figure 2, amplifiers A 4 and A 5 amplify the bridge signals and A 6 gives the "moment" M_z which is measured by the weight detection network described below.
Block 4 The weight detection network will produce the "sample & hold" and "A/D convert" commands to the functions of Box 5 as soon as the basic requirements for a "TAKEWT" interval are satisfied (i.e. correct F , M_z and time). The sample & hold network is used to assure a "smooth" input to the converter and will avoid any errors due to spurious signal variations during the convert interval. In Figure 2, A 7 is a summing amplifier and will add the signals from A 1 and A 2 (the two F_z bridges). If the two signals are the same polaritiy, A 7 will give a large output and if they are of opposite polarity, they will cancel each other, in which case A 7 will have little or no output. Amplifier A 8 is configured as a window .comparator; Diodes D 1 thru D 4 provide a window voltage of ± V_d, with D 1 and D 3 detecting the M moment and diodes D 2 and D 4 detecting the M _z moment. If both moments are inside the ± V_d window, A 8 produces a "high" output, which will enable one input of the "AND" gate, therefore satisfying conditions (1) and (2) of the "TAKEWT" requirements. It also enables the time delay counter of Box 1. The third condition for "TAKEWT" comes from the time delay function (Box 1) and the M 1 monostable will produce a pulse T 1 if the output of A 8 remains in the high state for the required length of time. This signal enables the second input of the "AND" gate. The fourth and final condition for "TAKEWT" is provided by amplifier A 9, which is configured as a comparator. A 9 looks at the resident threshold of release and compares it with the weight signal from amplifier A 7. If A 7 is greater than the present value for THDREL, A 9 goes high, therefore enabling the third input to the "AND" gate. With all three inputs high, the "AND" gate output goes high, therefore providing the command inputs to Box 5.
Block 5 Figure 1 shows a sample & hold and an A/D converter in a single box. The A/D converter will change the analog value for weight into its digital equivalent. The digital equivalent is most useful here because of its ability to maintain long time storage'without the deterioration experienced in analog memory functions. In Figure 2, the command signal from Box 4 will last for T 1 seconds and will first close - switch SW 1, allowing capacitor C 1 to charge and store the weight signal. This sample & hold function will provide a smooth input to the converter as mentioned above. The end of T 1 will activate the converter, whose digital output is fed to the D/A converter of Box 6.
Block 6 In both Figure 1 and Figure 2, when the A/D converter completes its conversion cycle, the "End of Convert" (EOC) pulse will latch the digital data at the input to the D/A converter of Box 6. The system is now assured of a stable, long time storage for the weight of the skier. The D/A output provides one inpuL to the summing amplifier of Box 9, which will then form the resident value for the threshold of release.
Block 7 In both Figure 1 and Figure 2, an UP/DOWN counter with preload capability is used to provide the initial threshold of release (when power comes on and prior to taking weight), and also to monitor the steering signal window to produce the threshold - changes as described earlier. The inputs to the counter comprise the n-bit digital word and the load command for the threshold along with the three control inputs labeled "Enable", "U/D" and "Clock". The three latter inputs come from Boxes 12, 14, and 15 respectively, and activation of these inputs will depend on the magnitude of the 'steering signals as described earlier. In general, however, the "Enable" input determines whether or not the counter is active; A "high" on the U/D port will cause it to count up, and a"low" to count down, when the "Clock" port sees a negative going transition.
Block 8 In Figure 1 and Figure 2, Box 8 is a D/A converter to provide the second input to summing amplifier 9. If weight has not been taken, this is the only active input to Box 9 and the system will begin its processing function on this value for the threshold. As soon as weight is taken, the combined signal will give the correct threshold for this particular skier. If the skier fails to take his weight, this function will eventually adjust to the correct treshold by monitoring the skier's steering signals. If at some later time a successful "TAKEWT" occurs, the counter 7 is reloaded with the minimum threshold so the correct sum will result.
Block 9 In Figure 1 and Figure 2, this is a summing function that combines the weight signal with the minimum threshold to give the resident threshold of release. The output of Box 9 provides the signal level on which the steering window is generated. The three lesser levels, UPERLIM, MEDIAN and LOLIM determine the window on which variations to this very same threshold are determined. THDREL also goes to the integrator of Box 21 and provides the level of moment, above which integration will begin in response to a dangerous situation.
Block 10 In Figure 1, defined as the steering window network, this function will establish and assure that the allowable range of THDREL (and consequently the steering window) will never exceed a maximum upper limit, or a minimum lower limit, regardless of skier weight and/or ability. Generally speaking, these limits are set at values below which none of normal health would ever be in danger, and above which almost everyone of normal health would surely be in danger. The output of Box 10 goes to Box 12, which determines when the UP/DOWN counter is either enabled or disabled for steering window corrections. In Figure 2, this function is generated with the use of the three boxes labeled "A", "B" and "C". The weight determined threshold (or the minimum threshold if weight is not taken) is used by Box "A" which increases the threshold by a percentage that is considered to be the maximum acceptable value, while Box "B" decreases the threshold a percentage below which the signals are virtually of no interest. Box "C", a window comparator, then prevents signals outside the range from making threshold corrections by disabeling UP/DOWN counter 7 through the OR gate in Box 12.
Blocks 11, 12, 13, 14 & 15 In both Figures 1 and 2, and as described earlier, the analog equivalent of the resident threshold of release (THDREL) is now devided into three separate processing levels: UPERLIM, MEDIAN and LOLIM. The respective magnitudes of these thresholds (as derived from THDREL) are set at a predetermined value below THDREL; The values selected depend on the resident threshold and may, in fact, be a non-linear relationship, whose characteristics depend on the most recent technical understanding of what the human leg can withstand. In Figure 2, these functions are made with the use of three comparators that will detect moments greater than the level in question. In Box 11, if UPERLIM is exceeded, the output goes high and will cause the output of the latch (Box 12) to go high, and a high on the "Enable" input of the UP/DOWN counter will disable the counter, therefore no change can occur. In Box 12, if MEDIAN is exceeded, the latch of Box 14 goes high, and the counter will count UP when it is finally clocked. In Box 15, when the signal falls below LOLIM, the output goes low again and the negative going edge will clock the counter UP if Box 14 is high, and DOWN if Box 14 is low. If Box 15 never goes high, nothing happens.
Block 16 The rate at which the steering signals increase is also important in detecting the quality of the skier. An advanced, high speed skier will generally generate sharper signals, but because of his expertise, the magnitude of the signals may not be as large as they are for a less proficient skier. Thus, the gradient detector will determine this and other qualities, and in so doing, an additional influence to the release characteristics is included in the processor performance. In Figure 2, when monostable M 2 detects the leading edge of LOLIM, a valid moment signal is occuring, and a pulse (T 2) of predetermined unit time is generated, for example 1 millisecond. T 2 closes switch SW 2, and it is noted that the absolute value networks (and the path to capacitor C 2) are designed to have minimum impedance, therefore C 2 will follow the increase in moment voltage with no (or very little) error. Hence, when T 2 ends and SW 2 opens, the voltage on C 2 will be representative of the average volts per millisecond rate of increase on the input moment signal. The length of T 2 is selected to be shorter than the expected length of LOLIM, which can be in the neighborhood of perhaps 10 milliseconds to one second. It is seen then, that V can have values of millivolts per second to volts per second, depending on the speed and length of the moment signal. V , the gradient, is then compared to the resident gradient shown at the output of D/A Box 19. If the new gradient is larger than the resident gradient, amplifier A 10 goes high, therefore setting the UP/DOWN port of -counter 17 to a high level and, when T 2 ends, the counter will clock up one count. Conversely, if amplifier A 10 is low, counter 17 will count down. In this way, the resident gradient will be in a perpetual state of high resolution adjustment to meet the demands of the skier. When LOLIM ends, switch SW 3 will close and C 2 will be discharged in preparation for the next steering signal.
Block 17 The gradient UP/DOWN counter was included in the discussion of Box 16 and performs in the same way as the steering UP/DOWN counter Box 7. Box 17 is also disabled when the moment signal exceeds UPERLIM and no change to the gradient is made.
Block 18 In this embodiment of the system, the M and M moments can be either plus or minus. In Figure 2, the absolute value networks convert the signal to a positive polarity only and diodes D 5 and D 6 will permit only the larger (or more dangerous) of the two moments to be processed by the processor. The resulting moment is then sent to the gradient network and the window comparators for steering signal interrogation. Independent processing of each of the moments has been the standard approach in the binding development, however, either method is effective and the one that is used will depend on experimental evidence involving the capability of the leg to withstand various combinations of torsional loads.
Block 19 In Figure 1 and Figure 2, this is the D/A converter for providing the analog equivalent of the gradient signal. Box 19 represents the third D/A converter in the embodiment described here. It is possible to use only one converter and to multiplex the three signals into the converter, and to then store the analog outputs in sample & hold networks. The approach that uses the least amount of electronic functions and power input will be the approach used in any particular design.
Block 20 This function, a summing amplifier, combines the THDREL and GRADIENT signals to determine the final voltage at which release occurs. Figure 2 shows amplifier A 11 going to release comparator Box 22. If this input to A 13 increases, then, in order for A 13 to provide a release command, the integrator A 12 will have to integrate for a longer period of time in order to produce enough voltage to activate A 13, which is the desired result; i.e. a largei gradient (sharper steering signals) will require that a given moment be exerted for a longer period of time in order for a release to occur.
Block 21 An integration function is provided to determine the release criteria as a function of both magnitude and time. This function has two inputs; The first input is the steering moment, but the integrator will not respond unless the second input, the threshold of release, is exceeded. The rate at which the integrator output increases will then be a function of the difference in magnitude between the moment and the THDR_EL value. Figure 2 shows amplifier A 12 configured as a differential integrator, where C 4 and R_in determine the time constant of integration, a value that is' selected on the basis of the desired release curve characteristics. So long as the moment (+) exceeds the THDREL (+), the output of A 12 will move in a negative direction, again, the rate depending on the difference between the two inputs. Conversely, when the moment falls below the THDREL, the integrator output will change direction and integrate back toward zero, the rate again depending on the difference. To make sure the integration stops when the A 12 output reaches zero (i.e. does not go positive), diode D 1 will latch the output from going positive by "shorting" C 4 for positive voltages.
Block 22 Mentioned above, the release comparator will produce the release command when the integrator output exceeds the reference threshold, which is comprised of the THDREL and GRADIENT signals.

Figure 3:

A graphical representation of the steering window variation is given. A similar graph for the change in the GRADIENT level can also be shown.

Time 1 The binding is latched, but the conditions for a weight signal have not yet been satisfied., therefore, a predetermined minimum threshold is established in the processor.
Time 2 The conditions for taking weight have been satisfied, the TAKEW-T signal triggers the A/D converter and the new thresholds are stored.
Time 3 A steering signal is generated, but it is too small to exceed LOLIM, therefore nothing changes.
Time 4 A steering signal is generated, whose value is greater than both LOLIM and MEDIAN. At the termination of the signal (when it goes below LOLIM), the thresholds are increased accordingly.
Time 5 Another steering signal is generated, where-both LO_LIM and MEDIAN are exceeded, and again the thresholds are increased at the termination of the signal.
Time 6 The next steering sigral is greater than LOLIM but smaller than MEDIAN, and now the thresholds are decreased at the termination of the signal.
Time 7 The last steering signal shown in the diagram exceeds the UPERLIM level, and consequently, the integration system is activated; Regardless of the outcome (release or no release), no change in the thresholds will occur.

The steering concept disclosed here has been reduced to practice and the desired results were observed when evaluated in the Marker Electronic Binding system. It is noted that many variations to the system described are possible, for example:

1. The rate at which the THDCNT and GRADIENT change (as a result of an input steering signal) could be made to depend on the actual magnitude of the moment signal. Hence, for a large moment and/or a large gradient, the counters could be made to increment a number of steps related (linearly or non linearly) to the magnitude of the signal.
2. The change to the subject signals (THDREL and GRADIENT) could be made to change for the entire time the signal exceeds the LOLIM value.

Claims

1. A safety ski binding comprising force transducers, which derive analog electric signals from the vertically acting forces occurring in the ball and heel portions of the skiing boot and from the torques acting on the skiing boot, an electronic circuit or a microprocessor for converting said signals into a value which depends on the magnitude and duration of the signals, and a comparator circuit for comparing said value with a threshold value which corresponds to permissible stresses and for generating a signal for initiating the release of the binding when said threshold value is exceeded, characterized in that an electric circuit is provided, which detects those of the forces sensed by the force transducers which act in the same sense in a vertical direction during the time for which these forces are acting when no torques are being detected and said circuit detects said forces as the weight of the skier if said forces are quasistatic, and that another circuit is provided which in accordance with a predetermined program sets the release value in dependence on the measured weight of the skier.

2. A safety ski binding according to claim 1, characterized in that the sum of the forces measured by the front and rear force transducers is formed.

3. A safety ski binding according to claim 1 or 2, characterized in that a circuit is provided in which torques between the range of torques which are due to force surges exerted during skiing and the range of torques acting for such a long time as to be dangerous to the leg, are detected as torques which are due to controlling forces and in said circuit the threshold value is set in accordance with a predetermined program to a value which is higher or lower than the threshold value that is due to the weight.

4. A safety ski binding according to claim 3, characterized in that the threshold value is not changed in response to those torques which are near the respective threshold value and are detected as torques which are due to controlling forces.

5. A safety ski binding according to any of claims 1 to 4, characterized in that the forces measured by the force transducers are summed or integrated in dependence on the gradient of the force increase with time to compute the release value which is to be compared with the threshold value and quickly increasing forces are integrated less rapidly than slowly increasing forces.

6. A safety ski binding according to claim 3 or 4, characterized in that the torques produced by the controlling forces result in a change of the threshold value only within a range which is limited by an upper limit and a lower limit for the threshold value.