Swing type machine and method for setting a safe work area and a rated load in same

A method for setting a safe work area and a rated load in a swing type work machine, as well as a swing type work machine which utilizes the said method, are disclosed. An area where a strength-based safe work area which is established taking the strength of a swing member into account and a stability-based safe work area which is established taking the stability of the work machine into account overlap each other, is set as a safe work area to be used actually. Likewise, out of a strength-based rated load which is set taking the strength of the swing member into consideration and a stability-based rated load which is set taking the stability of the work machine into consideration, the lower one is set as a rated load to be used actually. Using the safe work area and rated load thus obtained, there are made a safety control and an appropriate display. According to this method, in a swing type work machine such as a crane, it is possible to establish a safe work area and a rated load both matching the actual hoisting capacity of the work machine.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a swing type work machine such as a crane
 having a swing member provided with a boom or the like, as well as a
 method for setting a safe work area and a rated load according to a
 working state of the machine.
 2. Description of the Related Art
 Generally, in such a swing type work machine as above it is required, from
 the standpoint of safety, to prevent breakage and tipping during a swing
 work of the machine, and as means for satisfying such requirement it is
 very important to properly set a rated load and a safe work area, or a
 limit working radius, for operating the machine safely.
 In the above rated load and safe work area there are included a
 strength-based rated load (safe work area) which is set taking the
 strength of each component into account and a stability-based rated load
 (safe work area) which is set taking the stability of the work machine
 into account. In determining the former, i.e., strength-based rated load
 (safe work area), importance is attached to the strength of a swing member
 such as a boom which becomes most disadvantageous in strength during a
 swing work, and a rated (safe work area) is established on the basis of
 the said strength. On the other hand, the latter, i.e., stability-based
 rated load (safe work area) is established for the purpose of preventing
 the tipping of the work machine during a swing work. Therefore, this rated
 load (safe work area) inevitably varies depending on the direction of the
 swing member such as a boom.
 All of the above rated loads (safe work areas) are extremely important
 parameters in ensuring the safety of the work machine. According to the
 prior art, minimum values of the above strength-based rated load (safe
 work area) and stability-based rated load (safe work area), (more
 particularly, rated loads or safe work areas in a sideways protruded state
 of the boom in which the work machine is most likely to tip), are
 calculated and the smaller rated load (safe work area) is adopted as a
 safety parameter to be used actually, then a swing control or warning is
 performed in accordance with the thus-adopted rated load (safe work area).
 In FIG. 13, strength-based safe work areas and stability-based safe work
 areas, which are calculated in an actual crane, are indicated by broken
 lines 91 and dash-double dot lines 92, respectively. More specifically, in
 a polar coordinate plane with a work radius and a wing angle as variables,
 strength-based safe work areas and stability-based safe areas, which
 correspond to specific hoisting loads, are shown in terms of contour
 lines.
 In the same figure, O denotes a swing center of the swing member in the
 crane, FL denotes a support point by an outrigger jack protruded at the
 left front portion of the crane, FR denotes a support point by an
 outrigger jack protruded at the right front portion of the crane, RL
 denotes a support point by an outrigger jack protruded at the left rear
 portion of the crane, and RR denotes a support point by an outrigger jack
 at the right rear portion of the crane.
 As noted above, since the strength-based safe work area is set taking the
 strength of the swing member of the boom or the like into account, its
 limit work radius is independent of the swing angle and the larger the
 hoisting load, the smaller the limit work radius. Therefore, the
 strength-based safe work areas corresponding to hoisting loads assume the
 shape of such concentric circles as shown by the broken lines 91 in FIG.
 13.
 On the other hand, the stability-based safe areas are set for preventing
 the tipping of the entire crane, so their schematic shapes describe a
 square contour line diagram surrounded with straight lines nearly parallel
 to tipping lines. Further, when a deformation of the boom is taken into
 account, there are described generally square shapes surrounded with
 curves which are centrally expanded somewhat outwards to an extent
 corresponding to the boom deflection rather than with straight lines
 parallel to tipping lines, as indicated by dash-double dot lines 92 in
 FIG. 13. The "tipping line" indicates a rotational center line at the time
 of tipping of the crane. For example, a tipping line in the left-hand side
 direction is a straight line connecting the support points FL and RL.
 Thus, the stability-based safe work area originally assumes an irregular
 shape, so even at the same hoisting load, there ought to be different safe
 work areas or rated loads between the case where an article is hoisted
 sideways and the case where it is hoisted obliquely forward or obliquely
 backward. In a conventional crane or the like, however, a certain limit
 work radius, i.e., the smaller work radius between a minimum value of a
 limit work radius which depends on strength and a minimum value of a limit
 work radius which depends on stability, is established throughout the
 whole circumference, so the hoisting work particularly at an obliquely
 front position or an obliquely rear position is limited to a greater
 extent than necessary and hence the capacity thereof is not fully
 exhibited. This is also the case with setting rated loads.
 In Japanese Patent Laid Open No.5,116889 ( a Japanese Patent Application
 corresponding to U.S. Pat. No. 5,217,126; hereby fully incorporated by
 reference) there is disclosed a device in which when outrigger jacks are
 protruded non-uniformly right and left, a safe work area is deformed into
 a shape other than a circle according to the protruded states. But this
 work area deformation takes into account only such non-uniform protrusion
 of outrigger jacks. Also in the said device, when all the outrigger jacks
 are protruded uniformly, certain limit work radium and rated load are set
 throughout the whole circumference. Thus, it cannot be said that the
 device disclosed in the above publication provides an effective measure
 for solving the foregoing problem.
 SUMMARY OF THE INVENTION
 It is an object of the present invention to provide a method capable of
 setting a safe work area and a rated load both matching an actual hoisting
 capacity of a swing type work machine such as a crane, as well as a swing
 type work machine capable of making an appropriate safety control and a
 useful display with use of the so-set safe work area and rated load.
 According to the present invention there is provided a method of setting a
 safe work area for safely operating a swing type work machine in which an
 article is suspended at a predetermined position of a swing member. In
 this method, a safe work area which is set in consideration of the
 strength of a swing member and which is circular centered on a rotational
 center of the swing member, is assumed to be a strength-based safe work
 area, while a safe work area which is set in consideration of the
 stability of the work machine and whose limit work radius changes
 depending on the swing angle of the swing member, is assumed to be a
 stability-based safe work area, and an area where both said safe work
 areas overlap each other is established as a safe work area to be used
 actually.
 According to the present invention there is provided a swing type work
 machine for realizing the method of setting the above safe work area, with
 an article being suspended at a predetermined position of a swing member.
 The swing type work machine is provided with a hoisting load detecting
 means for detecting a hoisting load of the swing member and an area data
 output means which outputs an area data of a safe work area to be used
 actually, the said safe work area being an area where a strength-based
 safe work area and a stability-based safe work area overlap each other,
 the strength-based safe work area being set taking a hoisting load and the
 strength of the swing member into account and being circular centered on a
 rotational center of the swing member, the stability-based safe work area
 being set taking the stability of the work machine into account and whose
 limit work radius changes depending on a swing angle of the swing member.
 In the above method and the above swing type work machine which adopts the
 said method, there is used a combination of the strength-based safe work
 area whose limit work radius is constant irrespective of the swing angle
 and the stability-based safe work area whose limit work radius changes
 depending on the swing angle, that is, there is used a useful safe work
 area matching the capacity of a crane which is used actually.
 Preferably, the stability-based safe work area is an area surrounded with
 straight lines parallel to tipping lines in the work machine or lines
 similar thereto. In the case of a work machine whose tipping directions
 are substantially limited to front, rear and right, left directions like,
 say, a wheel crane provided with outrigger jacks, a line as a tipping
 center of the crane in the case of the crane tipping in any of front, rear
 and right, left directions corresponds to each "tipping line." In this
 case, therefore, the stability-based safe work area assumes a rectangular
 shape or a shape similar thereto. On the other hand, in the case of a work
 machine whose tipping directions are not limited to front, rear and right,
 left directions, like a crawler crane, the shape of the line in question
 is determined according to concrete tipping characteristics of the work
 machine.
 If a final safe work area is established within a circle whose radius
 corresponds to the maximum work radius of the swing member centered on the
 rotational center of the swing member, the safe work area will be a
 practical safe work area which matches the actual situation more closely.
 Preferably, the foregoing area data output means has a memory which stores
 three-dimensional data using as variables the work radius and swing angle
 of the swing member and the corresponding rated load, and it calculates
 and outputs a corresponding safe work area from the hoisting load detected
 by the hoisting load detecting means. According to this construction, the
 safe work area is outputted rapidly on the basis of the stored data.
 In the case where the swing type work machine is provided with outrigger
 jacks protruded in the horizontal direction, the above area data output
 means preferably has a memory which stores plural kinds of
 three-dimensional data according to protruded states of the outrigger
 jacks. This construction permits a rapid output of a safe work area
 suitable for the actual protruded state of the outrigger jacks.
 Preferably, the swing type work machine is provided with a work radius
 detecting means for detecting an actual work radius of the swing member, a
 swing angle detecting means for detecting an actual swing angle of the
 swing member, and a safety control means which makes control to let the
 work machine perform safe operations on the basis of a comparison of the
 safe work area outputted from the area data output means with actual work.
 radius and swing angle.
 In this swing type work machine, an appropriate safety control is conducted
 on the basis of the safe work area calculated in the above manner.
 For example, the safety control means may be a warning control means which
 issues a warning when the work position has approached a boundary line of
 the safe work area, or it may be provided with a swing control means which
 makes control so that a swing brake is applied at a predetermined timing
 to stop the swing member within the safe work area. In the latter case,
 the swing member can be automatically prevented from departing from the
 safe work area.
 Preferably, the swing control means is provided with a brake angle
 acceleration calculating means for stopping the swing member without
 permitting any residual deflection of a suspended article, and makes
 control so that the rotation of the swing member is braked on the basis of
 the brake angle acceleration thus calculated. According to this
 construction, not only the swing motion can be stopped but also the
 suspended article can be brought to a standstill, thus enhancing the
 safety to a greater extent.
 Preferably, the swing type work machine is provided with a work radius
 detecting means for detecting an actual work radius of the swing member, a
 swing angle detecting means for detecting an actual swing angle of the
 swing member, and a display means which displays on a single display
 screen the relation of the safe work area outputted from the area data
 output means to actual work radius and swing angle.
 According to this construction, the safe work area established in the above
 manner is displayed together with the current working condition, and thus
 useful information is provided to the operator of the work machine.
 The display means may be of a construction wherein the safe work area is
 displayed three-dimensionally in a cylindrical coordinate system using as
 variables the work radius and swing angle of the swing member and the
 corresponding rated load, or it may be of a construction wherein a safe
 work area corresponding to an actual hoisting load is displayed on a polar
 coordinate plane using the work radius and swing angle of the swing member
 as variables. In the former case, the relation among the work radius,
 swing angle and rated load can be grasped at a glance, while in the latter
 case it becomes easier to grasp the relation between the current work
 position and the safe work area.
 In the latter case, moreover, the larger the actual hoisting load, the more
 enlarged the display of the safe work area, whereby the safe work area can
 be displayed enlargedly to the maximum extent irrespective of changes in
 actual size of the same area, thus providing a display which is easy to
 see for the operator.
 If the portion of the safe work area which has been established on the
 basis of the strength-based safe work area and the portion thereof which
 has been established on the basis of the stability-based safe work area
 are displayed in a distinguished manner, it becomes possible for the
 operator to judge exactly whether attention should now be paid to the
 strength or to the stability, thus permitting a more appropriate
 operation.
 According to the present invention there also is provided a method of
 setting a rated load of a swing type work machine with an article
 suspended at a predetermined position of a swing member. According to this
 method, out of a strength-based rated load which is set taking the
 strength of the swing member into account and which is constant
 independently of the swing angle of the swing member, and a
 stability-based rated load which is set taking the stability of the work
 machine into account and which varies depending on the swing angle of the
 swing member, the lower one is adopted for each swing angle and is set as
 a rated load to be used actually.
 According to the present invention there is further provided a swing type
 work machine for realizing the rated load setting method just mentioned
 above, with an article suspended at a predetermined position of a swing
 member. This swing type work machine is provided with a work radius
 detecting means for detecting a work radius of the swing member and a
 rated load data output means which outputs a rated load selected for each
 swing angle of the swing member as a rated load to be used actually, the
 said rated load being the lower one out of a strength-based rated load
 which is set taking the said work radius and the strength of the swing
 member into account and which is constant independently of the swing angel
 of the swing member and a stability-based rated load which is set taking
 the stability of the work machine into account and which varies depending
 on the swing angle of the swing member.
 In the method and the swing type work machine adopting the said method,
 both described just above, there is used the smaller one selected from the
 strength-based rated load which is constant independently of the swing
 angle and the stability-based rated load which varies depending on the
 swing angle of the swing member, that is, a useful rated load matching the
 capacity of the actual crane is used.
 Preferably, the rated load data output means has a memory which stores
 three-dimensional data using as variables to the work radius and swing
 angle of the swing member and a corresponding rated load, and it
 calculates and outputs a corresponding rated load from the work radius
 detected by the work radius detecting means. According to this
 construction, the rated load can be outputted rapidly on the basis of the
 stored data.
 Where the swing type work machine is provided with outrigger jacks
 protruded in the horizontal direction, the above rated load data output
 means preferably has a memory which stores plural kinds of
 three-dimensional data according to protruded states of the outrigger
 jacks. This construction permits a rated load to be outputted rapidly
 which load is suitable for the actual protruded state of the outrigger
 jacks.
 Preferably, the swing type work machine is provided with a hoisting load
 detecting means for detecting an actual hoisting load of the swing member,
 a swing angle detecting means for detecting an actual swing angle of the
 swing member, and a safety control means which makes control to let the
 work machine perform safe operations in accordance with a comparison
 between the rated load outputted from the rated load data output means and
 an actual hoisting load.
 In this swing type work machine, an appropriate safety control is executed
 in accordance with the rated load calculated in the above manner.
 A concrete example is making control to restrict the swing speed in
 accordance with a load factor which is the ratio of the actual hoisting
 load to the rated load. According to this construction, by restricting the
 swing speed to a great extent when the load factor is high, it is possible
 to restrict the deflection of a hoisted article and ensure a high safety.
 In this case, the gain of an actual swing speed relative to the amount of
 operation of a lever performed by the operator. But if the maximum swing
 speed alone is restricted, it becomes possible to make a swing control
 conforming to the operator's will when the lever is operated slightly to
 an extent not causing any obstacle in safety.
 Preferably, the swing type work machine in question is provided with a
 hoisting load detecting means for detecting an actual hoisting load of the
 swing member, a swing angle detecting means for detecting an actual swing
 angle of the swing member, and a display means which displays the rated
 load outputted from the rated load data output means or a value related
 thereto (say a load factor).
 According to this construction, the rated load which has been established
 in the above manner is displayed and there is provided information useful
 for the operator.
 In this case, if a display is made in a distinguishable manner as to
 whether the displayed value is based on the strength-based rated load or
 on the stability-based rated load, it becomes possible for the operator to
 judge exactly whether attention should now be paid to the strength or to
 the stability, thus making it possible to perform a more appropriate
 operation.

DESCRIPTION OF A PREFERRED EMBODIMENT
 A preferred embodiment of the present invention will be described
 hereinunder with reference to the accompanying drawings. Although a crane
 is disclosed herein as an example of a swing type work machine, the
 present invention is applicable to various work machines provided with a
 swing member.
 A crane 10 shown in FIG. 1 is provided with a swing frame 102 which is
 swingable about a vertical swing shaft 101, and a boom B comprising N
 number of boom members B1 to BN and capable of expansion and retraction is
 attached to the swing frame 102. The boom B is constituted so as to be
 pivotable (capable of rise and fall) about a horizontal pivot shaft 103,
 and an article C is suspended at the tip (boom point) of the boom B
 through a hoisting rope 104. In the following description it is assumed
 that Bn (n=1, 2, . . . , N) indicates the n.sup.th boom member counted
 from the swing frame 102 side.
 At the four, front, rear and right, left corners of a lower frame of the
 crane 10 are disposed outrigger jacks 105 which are protruded sideways. It
 is optional whether the outrigger jacks 105 are to be set each
 individually or all uniformly with respect to the amount of their
 horizontal protrusion. In the case of a large-sized crane, the number of
 outrigger jacks may be larger, and the outrigger jacks may protrude
 obliquely sideways.
 In the crane 10, as shown in FIG. 2, there are disposed a boom length
 sensor 11, a boom angle sensor 12, a cylinder pressure sensor 13,
 outrigger jack horizontal protrusion quantity sensors 14, a swing angle
 sensor 15, a swing angular velocity sensor 16, and a rope length sensor
 17. Detected signals provided from these sensors are inputted to an
 arithmetic and control unit 20, which in turn outputs control signals to
 an alarm 31 such as a lamp, a buzzer or any other audio output device,
 also to a display device having a display screen such as LCD or CRT, and
 further to an electromagnetic proportional valve or the like used in a
 hydraulic circuit 33 for swing drive.
 FIG. 3 shows a functional configuration of the arithmetic and control unit
 20. As shown in the same figure, the arithmetic and control unit 20 is
 provided with a work radius calculating means 21, a hoisting load
 calculating means 22, a load factor calculating means 23, a safe data
 output means 24, a residual angle calculating means 25, a brake angle
 acceleration calculating means 26, a required angle calculating means 27,
 a margin angle calculating means 28, a limit speed setting means 29, a
 warning control means 30A, a swing drive control means 30B, and a
 hydraulic drive control means 30C.
 In FIG. 3, the work radius calculating means 21, which constitutes a work
 radius detecting means, calculates a work radius R of the suspended
 article C on the basis of boom length LB and boom angle .phi. detected
 respectively by the boom length sensor 11 and the boom angle sensor 12.
 The hoisting load calculating means, which constitutes a hoisting load
 detecting means, calculates a load W based on the article C hoisted
 actually in accordance with the boom length LB, boom angle .phi., and a
 cylinder pressure, p, of the boom upper detected by the cylinder pressure
 sensor 13.
 The load factor calculating means 23 calculates the ratio of the actually
 hoisted load W to a rated load Wo at each swing angle .theta. outputted
 from the data output means 24 which will be described later, namely, a
 load factor W/Wo, on the basis of the data on the hoisting load W of the
 boom B calculated by the hoisting load calculating means 22, the swing
 angle .theta. detected by the swing angle sensor 15, and the said rated
 load Wo.
 The data output means 24 has a memory which stores three-dimensional data
 using as variables the three data of the above work radius R, swing angle
 .theta. and rated load Wo. On the basis of the said three-dimensional data
 the data output means 24 calculates and outputs a whole circumference
 rated load Wo (Wo is a function of the swing angle .theta.) which
 correspondings to the current work radius R, and also calculates a whole
 circumference limit work radius (a work radius based on the assumption
 that the current hoisting load W is the rated load Wo) Ro (Ro is a
 function of the swing angle .theta.) corresponding to the current hoisting
 load W and outputs it as data on a safe work area.
 In this embodiment, the memory of the data output means 24 can store plural
 kinds of three-dimensional data according to protruded states of the
 outrigger jacks 105 and boom lengths. The data output means 24 is
 constituted so as to access three-dimensional data corresponding to
 horizontal protrusion quantities d1.about.d4 of the outrigger jacks 105
 detected actually by the outrigger jack horizontal protrusion quantity
 sensor 14 and boom length LB and then calculate the rated load Wo and safe
 work area on the basis of the three-dimensional data.
 An example of such three-dimensional data is shown in FIG. 4 as a
 three-dimensional data corresponding to a fully protruded state of all the
 outrigger jacks 105. The three-dimensional data 40 is represented in a
 cylindrical coordinate system using Wo, out of R, .theta. and Wo, as a
 vertical axis. In this coordinate system, a strength-based safe work area
 41, which is set on the basis of the strength of the boom B for example,
 is represented in a three-dimensional, cone-like shape as a whole having a
 circular horizontal section, while a stability-based safe work area 42,
 which is set on the basis of the stability of the crane, is represented in
 a three-dimensional, quadrangular pyramid-like shape as a whole surrounded
 with lines parallel to tipping lines in various directions and having a
 square (rectangular in the figure) horizontal section. An area where the
 strength-based safe work area 41 and the stability-based work area 42
 overlap each other is set as such a final safe work area as illustrated in
 the figure.
 In this figure, the reference mark DL denotes a boundary line between both
 areas 41 and 42, and the numeral 43 denotes a contour line of each rated
 load (4 ton, 6 ton, 8 ton, . . . in the figure). The boundary line DL may
 be a line literally, or it may be rounded for smooth shift between both
 areas 41 and 42.
 More preferably, taking the maximum work radius of the boom B into account,
 the three-dimensional data 40 is assembled so that a safe work area is set
 inside the said maximum work radius, that is, within a cylinder having a
 radius corresponding to the said maximum work radius. The thus-assembled
 three-dimensional data 40 is shown in FIG. 5. The safe work area shown in
 this figure has a shape obtained by cutting off the outer peripheral
 portion of the safe work area shown in FIG. 4 by means of a cylinder
 having radius equal to the maximum work radius. A cylindrical surface 45
 represents a cut end.
 In FIG. 5, assuming that the current work point (boom point) is represented
 by point P, then on a section 44 which includes both point P and Wo axis,
 the height (Wo coordinates) of a point where a straight line extending
 just above from the point P and a three-dimensional surface indicative of
 the safe work area intersect each other is the rated load Wo. Likewise, R
 coordinates of a point where a straight line extending horizontally in a
 radially outward direction from the point P and a three-dimensional
 surface indicative of the safe work area intersect each other correspond
 to the limit work radius Ro at that work point.
 It is to be understood that the "three-dimensional data" as referred to
 herein is not limited to only those stored as three-dimensional images in
 the memory but widely indicate combined data using the three variables of
 work radius R, swing angle .theta. and rated load Wo. For example, the
 relation among R, .theta. and W may be stored in terms of a functional
 expression. According to another method, the work radius R for each unit
 swing angle (say 1.degree.) proportional to work conditions such as boom
 length LB and outrigger jack protrusion quantity is tabulated as a data
 table, then plural such tables are stored together as a data map, and a
 middle point is determined by interpolatory calculation. In the case where
 the data in question are to be used for control actually in each
 individual work machine, the latter method just referred to above is
 advantageous in that the time required for calculation can be made shorter
 than in the former method (calculation using a functional expression).
 The residual angle calculating means 25 calculates a residual angle .theta.
 c at which the boom B can swing within the safe work area from its current
 position.
 On the basis of the work radius R, boom length LB, boom angle .phi., and
 angular velocity .OMEGA.o and hoisted article deflection diameter LR which
 are detected by the angular velocity sensor 16 and the rope length sensor
 17, respectively, the brake angle acceleration calculating means 26
 calculates a brake angle acceleration .beta. which does not cause
 deflection of the suspended article C when the swing motion stops and
 which takes into account a lateral bending strength of the boom B against
 an inertia force in forced stop.
 On the basis of the angular velocity .OMEGA.o before the start of swing
 control, the required angle calculating means 27 calculates a swing angle
 (required angle) .theta.r of the boom B during the period from time when
 braking is started at the brake angle acceleration .beta. until when the
 swing motion stops. The margin angle calculating means 28 calculates a
 margin angle .DELTA..theta. which is the difference between the residual
 angle .theta.c and the required angle .theta.r.
 The limit speed setting means 29 calculates a limit value of the maximum
 swing speed on the basis of the load factor W/Wo calculated by the load
 factor calculating means 23. As to the contents of the calculation, it
 will be described in detail later.
 1 When the load factor W/Wo calculated by the load factor calculating means
 23 has become 90% or more and 2 when the margin angle .DELTA..theta.
 calculated by the margin angle calculating means 28 has becomes a
 predetermined value or less, the warning control means 30A outputs a
 control signal to the alarm 31, causing the alarm to issue a warning.
 The swing drive control means (safety control means) 30B outputs a control
 signal to, for example, an electromagnetic proportional valve included in
 the hydraulic circuit 33 for swing drive, thereby making a swing drive
 control for a rotatable superstructure. In normal operation, a control
 responsive to the contents of operation conducted by the operator is made
 within a swing speed range not exceeding the limit speed set by the limit
 speed setting means 29, and when the margin angle .DELTA..theta. has
 become zero, a swing brake for the boom B is started at the brake angle
 acceleration .beta.. On the other hand, the hydraulic drive control means
 30C outputs a control signal to an electromagnetic proportional valve
 included in the hydraulic circuit 34 which is for creating a motion (say
 rise and fall of the boom) other than the swing motion, thereby
 controlling the same valve.
 The following description is now provided about arithmetic and control
 operations carried out actually by the arithmetic and control unit 20.
 A. Arithmetic and Control relating to the Load Factor
 First, on the basis of the boom length LB and boom angle .phi. the work
 radius calculating means 21 determines a work radius R' not taking the
 deflections of the boom B, frame and outrigger jacks into account and an
 error .DELTA.R caused by the deflections of the boom B, frame and
 outrigger jacks, and calculates the work radius R from both R' and
 .DELTA.R. On the basis of the thus-calculated work radius R, boom length B
 and cylinder pressure p the hoisting load calculating means 22 calculates
 the load W of the article C hoisted actually.
 The data output means 24 selects three-dimensional data 40 corresponding to
 the current horizontal protrusion quantities d1.about.d4 of the outrigger
 jacks 105 and the current boom length LB and, on the basis of the data
 thus selected, calculates the rated load Wo throughout the whole
 circumference in the form of a function, f(.theta., R), of the swing angle
 and work radius. (Of course, only the rated load Wo corresponding to the
 current swing angle .theta. and work radius R may be calculated every
 moment.) As to the rated load Wo thus calculated, out of a strength-based
 rated load (a constant rate load throughout the whole circumference
 independently of the swing angle) which is set taking the strength of the
 boom B into account and a stability-based rated load (a rated load small
 in the longitudinal and transverse directions and large in obliquely front
 and rear directions where the outrigger jacks are located) which is set
 taking the stability of the crane into account, the smaller load is the
 rated load adopted for each swing angle .theta. and work radius R. Thus,
 there is obtained an appropriate rated load matching the hoisting capacity
 of the crane used actually.
 The load factor calculating means 23 calculates the load factor W/Wo on the
 basis of the rated load Wo and hoisted load W corresponding to the current
 swing angle .theta. and work radius R.
 If the load factor W/Wo is 90% or more, the alarm 31 issues a warning upon
 receipt of an output signal from the warning control means 30A, so that
 the operator can become aware that the load W based on the hoisted article
 C is close to the rated load Wo. If the load factor W/Wo exceeds 100%,
 that is, if the actual load W exceeds the rated load Wo, not only the
 alarm operates but also a control signal is outputted from the hydraulic
 drive control means 30C in FIG. 3 to the hydraulic circuit 34, whereby
 crane motions by actuators in the hydraulic circuit 34, namely, crane
 motions (extension, rise and fall of the boom B, hoisting of the article
 C) except swing motion are stopped forcibly.
 On the other hand, in the limit speed setting means 29, a limit value of
 the maximum swing speed is calculated on the basis of the load factor
 W/Wo. More specifically, the limit speed setting means 29 stores such a
 relation between the load factor W/Wo and a maximum speed limit
 coefficient K as shown in FIG. 6, in the form of, for example, a
 mathematical expression or a map, then calculates the maximum speed limit
 coefficient K corresponding to the inputted load factor W/Wo, then
 multiplies this value K by the maximum swing speed, and outputs the
 resulting value as a limit speed to the swing drive control means 30B.
 In this embodiment, as shown in FIG. 6, the maximum speed limit coefficient
 K is set to 1 in the region wherein the load factor is below 50%. That is,
 the limitation of the maximum swing speed is not performed. On the other
 hand, in the region where the load factor is above 50%, the maximum speed
 limit coefficient K decreases as the load factor increases, and the degree
 of limitation on the maximum swing speed becomes larger. During operation
 at a high load factor, the boom B swings only at a low speed even if the
 operator fully operates the swing lever, thus ensuring high safety.
 Besides, this limitation is for the maximum swing speed and therefore as
 long at the operator operates the swing lever only a small amount, a swing
 control is made at a speed matching the amount of operation of the lever
 and thus priority is given to the operator's will.
 For actually limiting the maximum speed as above, a limitation may be
 placed on the control signal provided from the swing drive control means
 30B to, for example, the electromagnetic proportional valve in the
 hydraulic circuit 33, or an electromagnetic proportional valve may be
 incorporated beforehand in the hydraulic circuit 33 and a control signal
 for limitation may be applied to the electromagnetic proportional valve
 during operation at a high load factor.
 B. Arithmetic and Control Relating to the Safe Work Area
 The data output means 24 outputs a safe work area proportional to the
 hoisting load W, horizontal protrusion quantities d1.about.d4 of the
 outrigger jacks 105, and boom length LB. This safe work area corresponds
 to a horizontal section obtained by cutting the three-dimensional body
 shown in FIG. 5 horizontally at a vertical position corresponding to the
 current hoisting load W. When this FIG. 5 is seen planarly from above, the
 result is like FIG. 10. In FIG. 10, the numeral 43 denotes a contour line
 at each of various rated loads (4 ton, 6 ton, 8 ton, . . . ). The contour
 line 43 as it is serves as an external-form line of the safe work area
 corresponding to each of various hoisting loads. The safe work area in
 question is a lapped area between a circular strength-based safe work area
 wherein the limit work radius Ro is constant independently of the swing
 angle .theta. and a stability-based safe work area or an irregular shape
 surrounded with straight lines (or similar lines) parallel to front, rear
 and right, left tipping lines. Therefore, in the case of a relatively
 small hoisting load W, the safe work area assumes a shape obtained by
 cutting the four corners of the stability-based safe work area which is in
 a generally square shape with use of a circle having the maximum work
 radius or a circle indicative of the strength-based safe work area. In the
 case of a large hoisting load W, the safe work area assumes the shape of
 the very strength-based safe work area (namely, a cylindrical area). The
 safe work area thus established is an appropriate area matching the actual
 capacity of the crane used, allowing the hoisting capacity of the crane to
 be exhibited to the utmost extent.
 On the other hand, the brake angle acceleration calculating means 26
 calculates, through the following procedure, the brake angle acceleration
 .beta. which takes the lateral bending strength of the boom B and which
 does not cause a deflection of the hoisted article.
 1 Calculating the moment of inertia of the boom
 The moment of inertia, In, of each boom member Bn is calculated in
 accordance with the following expression:
EQU In=Ino.multidot.cos.sup.2 .phi.+(Wn/g).multidot.Rn.sup.2 (1)
 Where, Ino stands for a moment of inertia (a constant) around the center of
 gravity of each boom member Bn, Wn stands for own weight of each boom
 member Bn, g stands for a gravitational acceleration, and Rn stands for a
 swing radius of the center of gravity of each boom member Bn.
 2 Calculating an allowable angular acceleration
 An allowable angular acceleration .beta..sub.1 is calculated in the
 following manner.
 Generally, the boom B and swing frame 102 of the crane 10 have a sufficient
 strength, but as the boom length L.sub.B becomes larger, a large lateral
 bending force acts on the boom B which is attributable to the force of
 inertia generated at the time of swing brake. A strength-related burden
 caused by such lateral bending force is the largest in the vicinity of the
 swing frame 102 and therefore the evaluation of strength is here made on
 the basis of the moment created around the swing shaft.
 More specifically, given that the angular acceleration of the boom B at the
 time of swing brake is .beta.' and the swing angle acceleration of the
 suspended article C is .beta.", the moment N.sub.B caused by rotation of
 the boom B and acting on the center of the rotation is represented by the
 following expression (2):
 ##EQU1##
 Where, W stands for a hoisting load calculated by the hoisting load
 calculating means 22. Given that the rated load relating to the lateral
 bending strength of the boom B is Wo'(=Wo.multidot..alpha.', .alpha.'
 being a safety factor), an allowable condition for this strength is
 represented by the following expression (3):
EQU N.sub.B /R.sub.B.ltoreq.Wo where R.sub.B =L.sub.B cos .phi. (3)
 Substitution of the foregoing expression (2) into this expression (3) gives
 the following expression (4):
 ##EQU2##
 Thus, the maximum angular acceleration .beta.' which satisfies this
 expression (4) can be set as the allowable angular acceleration
 .beta..sub.1.
 The rated load Wo' may be set at a certain value, but it also may be set at
 a smaller value as the boom length L.sub.B and work radius R become
 larger, take the deflection of the like of the boom B into account.
 3 Calculating the actual angular acceleration
 The actual brake angle acceleration .beta. is calculated on the basis of
 the allowable angular acceleration .beta..sub.1 calculated in the above
 manner and the boom angular velocity (before deceleration) .OMEGA.o and
 hoisted article deflection diameter LR both obtained from the results of
 detection made by the angular velocity sensor 16 and rope length sensor
 17.
 This calculation is conducted in the following manner. First, with respect
 to the article C suspended in the crane 10, a model of such a simple
 pendulum as shown in FIG. 7 is considered. Differential equations of this
 system are given by the following expressions (5) and (6):
EQU .eta.+(g/L.sub.R).eta.=-V/L.sub.R (5)
EQU V=Vo+at (6)
 Where, .eta. stands for the deflection angle of the hoisted article C, V
 stands for the swing speed of a boom point which varies with time, t,
 V.sub.o stands for the swing speed (=R.OMEGA.o) before the start of swing
 stop of the boom point, and a stands for an acceleration thereof. If both
 sides of the above expression (5) is differentiated by time, t, followed
 by substitution into the right side of the same expression and subsequent
 integration under initial conditions of (t=0, .eta.=0, d.eta./dt=0), there
 is obtained the following expression (7):
EQU (.eta.+a/g).sup.2 +(.eta./.omega.).sup.2 =(a/g).sup.2 where
 .omega.=g/L.sub.R (7)
 If this expression is expressed on a phase plane relating to
 (d.eta./dt)/.omega., there is described a circle centered at point A
 (-a/g, 0) and passing through the origin O (0,0). The time required for
 circulating this circle, namely, the period T from the time when the state
 of the simple pendulum changes from the origin O up to time when it
 reverts to the original state, is given as T=2.pi./.omega., so if the
 angular acceleration .beta. is set so as to reach a complete stop in time
 nT (n is a natural number) after the time point (point O) at which the
 crane began to stop rotation, it is possible to stop the crane without any
 residual deflection of the hoisted article. On the other hand, since the
 above .omega. is a constant value determined by both gravitational
 acceleration, g, and deflection diameter LR, an angular acceleration
 .beta. which permits a rotation stop free of any article deflection can be
 obtained by the following expressions:
EQU .beta.=-.OMEGA.o/nT=-.omega..OMEGA.o/2n.pi.(n is a natural number.) (8)
 As to the lateral bending strength of the boom B, there exists the
 condition of .vertline..beta..vertline..ltoreq..beta.1, therefore by
 selecting a minimum natural number, n, in the range which satisfies the
 said condition, it is possible to obtain an actual brake angel
 acceleration .beta. for stopping the crane without hoisted article
 deflection and in a minimum time required.
 On the basis of the current angular velocity (before braking) .OMEGA.o the
 required angle calculating means 27 calculates a swing angle (required
 angle) .theta. r necessary from the start of braking until complete stop
 in the case where the stop of rotation is conducted at the above brake
 angle acceleration .beta.. More specifically, if the time required from
 the start of braking until complete stop is assumed to be t, there exist
 the following two expressions:
EQU .OMEGA.o+.beta.t=0,.theta.r=.beta.t.sup.2 /2+.OMEGA.ot (9)
 Therefore, the required angle .theta. r can be obtained by eliminating t
 from both expressions.
 The margin angle calculating means 28 calculates the angle at which
 rotation can be done at the current angular velocity .OMEGA.o until the
 start of braking, i.e., margin angle .DELTA..theta. (=.theta.c-.theta.r).
 The swing drive control means 30B outputs a control signal to the hydraulic
 circuit 33 when the margin angle .DELTA..theta. thus calculated has become
 zero, thereby making a swing brake for the boom B and a forced stop of
 operation involving an increase in work radius from the current radius. At
 this time, for preventing deflection of the suspended article C, a
 hydraulic motor pressure PB is set so as to stop at the foregoing brake
 angle acceleration .beta..
 An example of how to calculate the hydraulic motor pressure PB will now be
 shown. If the sum total of inertia moments related to the other components
 of the rotatable superstructure than the boom B is assumed to be Iu, the
 torque TB necessary for swing brake is given by the following expression
 (10):
 ##EQU3##
 The acceleration .beta." of the hoisted article C can be expressed in terms
 of the following expression by solving the foregoing expressions (3) and
 (5) at .eta.=0 and d.eta./dt=0 under the initial condition of t=0, though
 the details are here omitted:
EQU .beta."=(1-cos .omega.t)-.beta. (11)
 On the other hand, the torque TB is approximately in the relation of the
 following expression to the conditions adopted on the hydraulic motor
 side, through the details are here omitted:
EQU T.sub.b =(P.sub.B.multidot.Q.sub.h /200.pi.)i.sub.o /.eta..sub.m (12)
 Q.sub.h : motor capacity
 i.sub.o : total deceleration ratio
 .eta..sub.m : mechanical efficiency
 Therefore, by substituting this expression (12) into the above expression
 (10), it is possible to obtain the actual hydraulic motor pressure PB.
 On the other hand, when the margin angle .DELTA..theta. has become a
 predetermined value or smaller, not zero, the warning control means 30A
 outputs a control signal to the alarm 31, causing the alarm to issue a
 warning. Consequently, the operator can become aware that braking will be
 applied automatically after a slight rotation.
 C. Display Control
 Further, the arithmetic and control unit 20 outputs information signals on
 various values to the display device 32 and provides useful information to
 the operator. As to the contents of the display, various modes are
 conceivable. Several examples will be given below.
 1) First Display Example (FIG. 9)
 According to this display example, the three-dimensional data 40 shown in
 FIG. 5 is displayed as it is, as a safe work area, in a cylindrical
 coordinate system using R, .theta. and Wo as variable. In a display screen
 32a illustrated in FIG. 9, an angular position corresponding to the
 current swing angle .theta. is expressed by a section 44, and a point P
 corresponding to the current hoisting load W and work radius R is
 spot-displayed within the section 44.
 In this display screen, since R and W coordinate axes are fixed, the
 three-dimensional portion rotates about the W coordinate axis (vertical
 axis) (in the direction of arrows E). The position of the point P shifts
 horizontally with changes of the boom length and boom rise/fall angle and
 shifts vertically as the hoisting load W changes. A correlation between
 the actual work position and the safe work area can be grasped always at a
 glance. When the protruded state of the outrigger jacks changes, the
 three-dimensional data 40 also changes and the display on the screen is
 switched over immediately.
 According to such a three-dimensional display, not only the current load
 factor at the current work posture can be grasped, but also it is possible
 to grasp how the safe work area was changed after the swing motion.
 For example, in the case where the boom hoists an article of a maximum load
 factor falling under the safe work area at a swing angle corresponding to
 an oblique direction of the crane (a direction where an outrigger jack is
 present), (for example, when P1 is positioned between 42a and 42a" in FIG.
 11), since the stability is higher in the said direction than in sideways
 directions, the point of the current load factor P1 is displayed on the
 section 44 in the display screen and within a workable safe work area
 42a'. At the same time, the entire safe work area 45 including angles
 around the said swing angle. Therefore, the operator can easily understand
 that if the swing motion is performed at the current posture as it is, the
 safe work area will become narrower. On the basis of this understanding
 the operator can perform an appropriate operation of the crane.
 If a color liquid crystal monitor or the like is used as display means to
 display the strength-based safe work area 41 and the stability-based safe
 work area 42 distinguishably using different colors or example, it becomes
 possible for the operator to judge correctly whether attention should now
 be paid to the strength or to the stability and hence possible to effect a
 more appropriate operation.
 As shown in FIG. 9, if there is provided a load factor display portion 64
 of a color bar display whose color and position change depending on the
 load factor, or if there is provided a numerical value display portion 65
 which displays concrete current state values (e.g. hoisting load W, work
 radius R, load factor), the display screen can be made more useful.
 2) Second Display Example (FIG. 10)
 In this display example, the three-dimensional data 40 is displayed
 planarly on the R-.theta. polar coordinate plane. As shown in FIG. 10,
 safe work areas corresponding to various hoisting loads may be displayed
 overlappedly as contour lines 43 and only the line corresponding to the
 current hoisting load may be displayed with a thick line (in the same
 figure the line of 6-ton hoisting load is displayed with a thick line
 43a). Alternatively, only the safe work area corresponding to the current
 hoisting load may be displayed. In the latter case, if the safe work area
 is displayed on a larger scale as the hoisting load W becomes larger, that
 is, as the safe work area becomes narrower, thereby allowing the safe work
 area to be displayed always throughout the whole display screen, the
 display screen becomes easier to see for the operator. Also in this case,
 as is the case with the above first display example, if a color liquid
 crystal monitor or the like is used to effect a distinguished display
 using different colors for example, it becomes possible to display the
 strength-based safe work area and the stability-based safe work area in a
 clearly distinguished manner with curve DL as the boundary, thus making it
 possible to provide a more appropriate information to the operator.
 In this display screen, if there is displayed a picture 46 which centrally
 shows the crane simulationwise or a segment 47 which shows the work radius
 and swing angle, the operator can grasp at a glance to what degree the
 current state of operation is safe. Further, in order for the direction of
 the rotatable superstructure in the actual work machine to match the image
 on the display screen, if for example the schematic diagram of the lower
 portion of the crane and the safe work area are rotated with rotation of
 the machine while the said direction is fixed, it becomes easier to
 recognize intuitively the actual direction of the rotatable superstructure
 in the crane and the display.
 3) Third Display Example (FIG. 11)
 This display example is the display of only the portion of the section 44
 in FIG. 5 as an orthogonal coordinate plane of R-W. In this display
 example, a curve 41a which indicates the strength-based safe work area
 does not change even if the swing member rotates, but the curve 42a which
 indicates the stability-based safe work area changes in the swing radius
 direction with the said rotation (see the curves 42a' and 42a"). Also in
 this case, by displaying the curves 41a and 42a distinguishably using
 different colors for example, it becomes possible for the operator to
 judge exactly whether attention should now be paid to the strength or to
 the stability.
 4) Fourth Display Example (FIG. 12)
 A display panel 50 shown in FIG. 12a is provided with a work condition
 display section 51, an outrigger jack protruded state display section 52,
 and a switch section 53. In the work condition display section 51 there
 are provided not only display portions of boom angle, hoisting load, work
 radius and limit load (rated load), but also a load factor display portion
 54. In the load factor display section 54, as shown in FIG. 12b, there are
 provided load factor display lamps 55 for displaying load factors in
 plural stages, as well as a discrimination display lamp 56A which is
 turned ON when the current load factor is based on a strength-based rated
 load and a discrimination display lamp 56B which is turned ON when the
 current load factor is based on a stability-based rated load.
 According to this configuration, in the load factor display portion 54, not
 only the current load factor is displayed by the load factor display lamps
 55, but also whether the load factor has been calculated from the
 strength-based rated load or from the stability-based rated load is
 displayed discriminatively by either the discrimination display lamp 56A
 or 56B, thus permitting the operator to judge exactly whether attention
 should now be paid to the strength or to the stability. This is also the
 case with displaying only the rated load without displaying the load
 factor.
 It is optional whether the above display examples are to be adopted each
 alone or in combination with other display examples.
 While the invention has been described in detail and with reference to
 specific embodiments thereof, it will be apparent to one skilled in the
 art that various changes and modifications can be therein without
 departing from the spirit and scope thereof.
 The entire disclosure of the Japanese Patent Application No. 10-205553
 filed on Jul. 21, 1998 including specification, claims, drawings and
 summary are incorporated herein by reference in its entirety.