SAFETY DEVICE AND METHOD FOR SAFETY OF A MACHINE

Description

[0001] The present invention relates to a safety device and a method for safeguarding a machine, in particular a bending press, in which a first machine part executes a working movement along a first direction of movement against a second machine part in order to deform a workpiece which, when the first machine part acts, moves at least partially towards the first or second machine part in a second direction of movement crossing the first direction of movement.

[0002] A well-known method for the non-cutting machining of workpieces is bending or chamfering. In this process, a workpiece that is initially flat in the area of ​​the machining point is formed under pressure. In machining, machines are used for this purpose, which are generally referred to as bending presses. However, the invention is not limited to bending presses in the narrow sense and can also be used in bending presses, punching machines, cutting machines, and other machines in which two machine parts perform a dangerous working movement against each other.

[0003] In a bending press, the workpiece is essentially formed by pressing it against a die with a bending punch. The desired shape can be achieved by appropriately designing the bending punch and die. The bending punch is often a tool mounted on a first, movable machine part, while the die is mounted on a second, stationary machine part. However, since only the relative movement of the two machine parts is important, the die can alternatively be moved, or both machine parts can be moved against each other. The safety device according to the invention can be used in all of the aforementioned cases.

[0004] It's easy to understand that a bending press poses a significant risk to operating personnel, particularly the risk of crushing or even severed body parts. Accordingly, it has long been a practice to equip bending presses and similar machines with safety devices to prevent accidents as much as possible. Common safety devices for bending presses are non-contact devices, such as light barriers, light grids, or optical systems, which detect objects other than the workpiece being machined in the machine's working area and report them to a control system. In response to the detected objects, the control system performs a safety-related function. For example, the control system can stop or at least slow down the machine movement.

[0005] Standard safety devices protect operating personnel from injury caused by moving machine parts. However, the workpiece being produced can also pose a further danger if it moves during forming. Especially when bending larger workpieces, these move at high speed outside the actual working area of ​​the bending press and therefore pose a danger to the operating personnel that should not be underestimated. There is also the risk that a careless operator could become completely or partially trapped between the workpiece and the bending machine. For example, with complex sheet metal constructions, the workpiece must be guided and held by the operator during bending. In this case, it can happen that a finger or the entire hand becomes trapped between the workpiece and the machine outside the actual working area of ​​the machine.

[0006] In addition to the risk of injury to the operator, the moving workpiece can also damage the bending machine or be damaged itself if it collides with the machine.

[0007] EP 3 536 416 A1 proposes a method for monitoring a bending press, in which an operator is protected from becoming trapped between a section of a workpiece being produced that is pivoted upwards during the bending process. The method according to EP 3 536 416 A1 provides for monitoring, in addition to the actual working area between the moving machine parts of the press, an area in front of the moving machine parts by means of an additional protective device. The protective device is intended to provide timely warning of a possible entrapment or to trigger an appropriate safety-related reaction. Similar to the monitoring of the working area, EP 3 536 416 A1 proposes the use of an additional optical protective device with a transmitter and a receiver, between which one or more protective zones are defined.

[0008] US 2018 / 126682 A1 shows a device similar to EP 3 536 416 A1.

[0009] With optical protective devices, such as light barriers or optical systems, the protection zone is primarily defined by the beam path between the transmitter and receiver. The transmitter and receiver are positioned on the machine using support arms and aligned so that a beam path between the transmitter and receiver runs in front of a surface to be protected. In this way, simple protective zones can be defined in front of the machine parts outside the actual work area. Complex protective zones, in particular those adapted to the contours of the machine parts, are difficult or even impossible to implement in this way. Therefore, oversized protective zones are often defined for optical protective devices in order to cover complex work areas with linear protective zones.

[0010] In addition, it is not possible to attach holding arms for transmitters and receivers to every bending press, as these usually protrude beyond the system, which is not always possible, especially with existing systems.

[0011] It is therefore an object of the present invention to provide a safety device and an alternative method for protecting a machine in which a first machine part performs a working movement along a first direction of movement against a second machine part in order to deform a workpiece. In particular, it is an object to provide a flexible method and a flexible safety device that avoids the aforementioned disadvantages of optical protective devices and simultaneously enables sufficient, comprehensive, and cost-effective protection of the machine.

[0012] US 2017 / 146368 A1 discloses a tactile robot skin.

[0013] KR 2017 0120789 A shows a press brake with a pressure-sensitive sensor as a protective device for monitoring a working area between an upper machine part and a lower machine part of the press brake. The protective device stops the machine if an object is located on a workpiece in relation to the direction of movement of the upper machine part.

[0014] JP S51 92532 U shows another protective device for a press brake.

[0015] According to one aspect of the present disclosure, this object is achieved by a method according to claim 1.

[0016] According to a further aspect of the present disclosure, the object is achieved by a safety device according to claim 10.

[0017] It is therefore an idea of ​​the present invention to arrange a monitoring device not in front of a surface of the machine part to be monitored, but rather on or as part of the area to be monitored. In other words, it is not the area in front of a surface of the machine part that is indirectly secured via upstream safety areas, but the area itself. This makes it possible to use other technologies for monitoring, e.g. contact-based sensors that are arranged directly on the area to be monitored. The definition of the area to be monitored can thus be more flexibly and individually adapted to the respective machine. Sensor technology of this type can therefore be easily retrofitted to existing machines. In particular, the safety device does not increase the external dimensions of the machine, since no additional holding arms protruding from the machine need to be mounted.

[0018] In a further embodiment, the sensor can be a pressure-sensitive sensor.

[0019] Pressure-sensitive sensors can directly detect contact between an object and the machine part and provide a corresponding signal. Pressure-sensitive sensors are less susceptible to failure when monitoring a surface than other protective devices, such as optical devices that only monitor a surface indirectly. Pressure-sensitive sensors only react when contact has actually occurred. This prevents false triggering of the safety function, increasing availability.

[0020] In a further embodiment, the pressure-sensitive sensor may comprise at least one electrode made of a textile material.

[0021] A textile pressure-sensitive sensor has the advantage that it can be placed flexibly, like a skin, on the surface to be monitored. This allows even uneven surfaces, such as machine parts with curved housings, to be monitored.

[0022] In a further embodiment, the sensor can be a capacitive area sensor. A capacitive sensor has the advantage of also being able to detect approach. In addition to direct contact with the machine part, this method can also detect imminent contact. The flat arrangement also allows the definition of a protective zone tailored to the machine part to be protected.

[0023] Particularly preferably, at least one electrode of the capacitive sensor can be a housing part of the first machine part or the second machine part. This configuration has the advantage that the housing of the machine part to be monitored becomes part of the protective device. The sensor can thus be optimally adapted to the housing shape of the machine part to be monitored. In this case, the housing can also represent the outer surface of the sensor, while the other components can be housed inside the housing of the machine part. In this way, a surface of a machine part can be monitored without the sensor extending beyond the actual housing of the machine.

[0024] In a further embodiment, the sensor can be a spatially resolving sensor configured to generate the signal to the controller based on the spatial resolution. A spatially resolving sensor is a sensor with an active surface. The sensor can not only register contact or proximity to the active surface, but also the location on the active surface where this contact or proximity occurs. The area to be monitored can be precisely defined in this way, enabling individual configuration for a machine. Furthermore, the area to be monitored can be changed dynamically.

[0025] In a further embodiment, the control system can slow down, in particular stop, the working movement as a safety-related action.

[0026] The controller can thus essentially trigger the same safety-related actions as a controller responsible for monitoring the actual effective range. Advantageously, the same controller can therefore be used both for monitoring the actual effective range and for protection against moving workpieces.

[0027] In a further embodiment, the sensor can distinguish between at least two stages of approach or contact and report them to the control system.

[0028] This design allows different levels of proximity or contact to be distinguished. This design therefore contributes to further increasing monitoring flexibility.

[0029] It is understood that the features mentioned above and those to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the present invention.

[0030] Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description. They show: Fig. 1 a simplified representation of a press with a new safety device, Fig. 2 a highly simplified representation of a first embodiment of the new safety device in a side view of the press from Fig. 1 , and Fig. 3 a highly simplified representation of a second embodiment of the new safety device in a side view of the press from Fig. 1 .

[0031] In Fig. 1 A press is designated as a preferred machine for the new safety device in its entirety with the reference numeral 10. However, it should be noted that the present invention can be used not only in presses, but also in other machines in which two machine parts execute a working movement against each other in order to deform a workpiece which, when the machine parts act on it, moves at least partially towards the first or second machine part in a second direction of movement crossing the first direction of movement.

[0032] The press 10 has an upper tool and a lower tool. Typically, the upper tool is the moving, first machine part 12 within the meaning of the present invention, and the lower tool is the second machine part 14. Reference numeral 16 represents a simplified representation of two drives with which the upper tool 12 can be moved in the direction of an arrow 18 against the lower tool 14. A bending tool 20 is arranged on the upper tool 12. Reference numeral 22 represents a simplified representation of a two-hand switch, which must be operated with both hands to start and execute a work cycle of the press 10. Alternatively, the press 10 can also be operated using suitable foot switches or other actuating elements.

[0033] A die 24, on which a workpiece 26, for example a sheet metal part, rests, is arranged on the lower tool 14. The lower end of the bending tool 20 is complementary to the die 24 and enables chipless forming of the workpiece 26 as it is moved into the die 24 (see FIG. Fig. 2 ).

[0034] Reference numerals 28 and 30 designate two holders arranged to the left and right of the bending tool 20 on the upper tool 12. A transmitter (not shown separately here) is located at the end of the holder 28, and several receivers (not shown separately) are located at the end of the holder 30. The transmitter and receiver form a light barrier arrangement that generates several light beams 32, 33. The light beams 32, 33 represent a first and a second optical barrier. They run approximately parallel to the lower edge of the bending tool 20 and are moved along with the upper machine part when it moves.

[0035] The first and second optical barriers represent a protective device in the conventional sense. The protective device monitors a working area between the upper machine part 12 and the lower machine part 14 and stops the machine if objects other than the valuable piece 26 are located within the effective range of the machine parts. The principle of such a protective device is generally known and will not be explained in detail below. Instead, a further protective device of the press 10 is described below, which complements the overall protection of the press.

[0036] The additional protective device constitutes a safety device within the meaning of this disclosure. It supplements the protection against hazards emanating from the moving machine parts with protection against hazards emanating from moving workpieces.

[0037] The further protective device has a sensor 36, which is arranged here on a surface 38 of the first machine part 12. The surface 38 of the first machine part 12 is in particular a surface of a housing 40 that encloses the first machine part 12. The sensor 36 has an active sensor surface 42 that extends over a defined surface section of the surface 38. The sensor surface 42 extends at least over a surface section on the surface 38 of the upper machine part 12, against which parts of the workpiece 26 to be machined can strike when the workpiece 26 is moved by the action of the bending tool 20. A typical movement of a workpiece 26 during the bending process as well as the function of the safety device is described below with reference to Fig. 2 and 3 explained in more detail.

[0038] The sensor surface 42 can extend over the entire surface 36 of the upper machine part 12, like a skin, and is not restricted to a limited surface section. The sensor surface 42 can be flexible and adapt to an uneven or curved surface 38 of the upper machine part 12. In particular, the sensor 36 can be a textile sensor that rests smoothly against the surface 36.

[0039] The sensor can be a pressure-sensitive sensor or a capacitive sensor. A pressure-sensitive sensor (also called a tactile sensor) can detect contact with the sensor surface 42. A capacitive sensor can detect approach to the sensor surface 42. A sensor that combines the properties of both of the above sensor types is also conceivable, i.e., a sensor that detects both contact with and approach to the sensor surface 42.

[0040] As an example of a pressure-sensitive sensor, a tactile sensor formed from multiple flexible layers is described below. The tactile sensor can comprise a first layer, a second layer, and a third layer located between the first and second layers. The first, second, and third layers are flat structures that, when placed flush with one another, form a pressure-sensitive sensor with a plurality of sensor cells.

[0041] The first, second, and third layers therefore extend over the entire surface. They can be fabric- or film-like. The flexible properties of the individual layers are preferably retained even when stacked, so that the tactile sensor forms a flexible unit that can be rolled up and processed similarly to a strip of fabric.

[0042] In addition to the three layers essential for the pressure-sensitive sensor, additional layers can be provided, such as a cover layer arranged above and below. The cover layer can be made of a waterproof material and protect the three layers from external influences. In particular, the cover layer can seal the layers against dust and water.

[0043] In preferred embodiments, the individual layers can be a few millimeters thick, for example, between 0.5 mm and 1.5 mm. However, the tactile sensor can have almost any surface area, from a few square centimeters to a few square meters.

[0044] The first layer and the second layer can be textile fabrics into which electrical structures are incorporated. For example, the layers are fabrics into which an electrical structure is incorporated using electrically conductive threads and electrically non-conductive threads. The electrical structure can define electrodes that, when placed on top of one another, form a matrix-like structure and form a multitude of sensor cells. The first layer and the second layer can be of the same type and obtained from a single workpiece. This enables particularly cost-effective and efficient production. The third layer is placed between the first and second layers. This can also be made of a flexible material, but does not necessarily have to be woven. The third layer can be a woven microfiber cloth whose fibers are coated with a conductive coating.The coating can be, for example, a carbon-based coating or a metallic coating.

[0045] A flexible, pressure-sensitive sensor, as described above, can simply be applied in one piece to the surface 38 of the first machine part 12. However, it is also conceivable that a plurality of individual pressure sensors are interconnected to form a flat structure in order to fill a surface section of the first machine part 12.

[0046] It is understood that the above description of a tactile sensor represents only one possibility for a pressure-sensitive sensor and the invention is not limited to this embodiment.

[0047] Alternatively or additionally, the sensor can also include a capacitive sensor. A capacitive sensor is a sensor that operates based on the change in the electrical capacitance of a single capacitor or a capacitor system.

[0048] A capacitive sensor can function as a pressure sensor and represents a possible alternative to the pressure sensor described above. In a capacitive pressure sensor, the change in capacitance due to the deflection of a membrane and the resulting change in the plate spacing is evaluated as a sensor effect.

[0049] However, the capacitive sensor can also function as a capacitive proximity switch. A capacitive proximity switch operates without contact, i.e., without direct contact, and detects the approach of a conductive or non-conductive object. The capacitive proximity switch utilizes the changing electrical capacitance of a measuring electrode to the environment or a reference electrode upon approach. The sensor typically includes an RC oscillator, whose frequency-determining capacitance is partially formed by the medium to be detected or the environment.

[0050] As with a pressure-sensitive sensor, a capacitive sensor can also extend over a surface section of the first machine part by distributing one or more sensor electrodes over the surface. It is also conceivable for the housing, or a section of it, to itself form an electrode of the capacitive sensor, thus becoming part of the sensor. In this way, the sensor can be particularly well adapted to the housing.

[0051] It goes without saying that the two sensor types described above can be combined to detect and distinguish between contact and approach. It is also conceivable for the sensors to be spatially resolving and, in addition to contact and / or approach, also determine where on the surface contact or approach has occurred. For this purpose, the sensors can be designed directly for spatially resolving evaluation thanks to their cell-like structure. Alternatively, a large number of sensors can be attached in a tile-like manner to the surface section to be monitored to enable this level of resolution. Among other things, spatial resolution enables the area to be monitored to be dynamically adapted.

[0052] In the following, with reference to Fig. 2 and Fig. 3 the procedure and the new safety device are explained in more detail. Fig. 2 shows a first embodiment with a pressure-sensitive sensor and Fig. 3 a second embodiment with a capacitive sensor.

[0053] As well as Fig. 2 as well as Fig. 3 show a section of the press 10 in a highly simplified side view. Parts with the same reference numerals as in Fig. 1 denote equal parts.

[0054] The side view shows an upper machine part and a lower machine part (first and second machine parts 12, 14), the bending tool 20, the die 24, and the workpiece 26. The upper machine part 12 and the lower machine part 14 have a housing 40 with a front side 46 and an opposite rear side 48. The front side 46 faces the machine operator.

[0055] As already mentioned in relation to Fig. 1 As described above, for a bending process, the upper machine part 12 and the lower machine part 14 move toward each other (first direction of movement 18). The workpiece 26 is pressed into the die 24 arranged on the lower machine part 14 by the bending tool 20, which is attached to the upper machine part 12, and the workpiece 26 is deformed according to the profile 44 machined into the die 24.

[0056] During deformation, the workpiece 26 moves. Sections of the workpiece 26 can move toward the upper or lower machine part 12, 14 and possibly touch it. More specifically, the workpiece can move toward the front side 46 of the first and second machine parts.

[0057] The front side 46 is equipped with the safety device 100. The safety device 100 comprises a sensor 36, which extends over a surface portion of the housing 40. In particular, the sensor 36 covers a surface portion of the front side 46 facing the machine operator. The active sensor surface 42 of the sensor 36 thus faces the machine operator, in this case in the Z direction.

[0058] The arrow with the reference number 50 indicates a direction of movement (second direction of movement) of a portion of the workpiece 26. The second direction of movement 50 separates the first direction of movement 18 in which the machine parts 12, 14 move. More precisely, here a portion of the workpiece 26 moves along the second direction of movement toward the front side 46 of the housing 40 of the upper machine part 12. The sensor 36 is arranged on a surface portion such that it lies between the moving portion of the workpiece 36 and the housing 40 of the upper machine part 12. Therefore, if the workpiece 26 were to move further along the second direction of movement 50 (not shown here), contact would occur with the housing 40 of the first machine part 12. This could damage the housing 40 and / or the workpiece 26.Furthermore, body parts could become trapped between the moving portion of the workpiece 26 and the housing 40.

[0059] To prevent this, the sensor 36 is arranged between the housing 40 and the moving section of the workpiece 26. The sensor 36 can cover the entire surface section of the housing 40, which is considered a potential contact surface in the event of a collision with the workpiece 26. If the moving section of the workpiece 26 collides with the sensor surface 42, the sensor 36 can detect this contact and generate a corresponding signal. Based on the signal, a safety-related reaction can be triggered, in particular an emergency stop of the machine 10 or the moving machine parts 12, 14 by switching off the drives 16.

[0060] The safety device 100 itself can have corresponding safe devices to trigger the safety-related reaction. However, the safety device 100 preferably only generates a corresponding output signal and transmits it to a controller (not shown here), which executes the safety-related reaction for the safety device 100. The controller can be the same controller that executes the safety-related reaction when monitoring the effective range of the machine. In particular, the controller is a fail-safe controller, e.g., of the PSS type, as marketed by the applicant.

[0061] The output signal can be configured as an enable signal. An enable signal is always transmitted when the sensor is functioning properly and no contact has been detected. A enable signal can be used to ensure that the machine 10 only starts or remains in operation when the enable signal is received from the controller. In all other cases, especially when no signal or a faulty signal is present, the controller stops the machine 10 or prevents it from starting.

[0062] The sensor 36 is in the embodiment according to Fig. 2 a pressure-sensitive sensor. The pressure-sensitive sensor can be the previously described multi-layered tactile sensor. Particularly preferably, the tactile sensor additionally has at least one further cover layer 52, which protects the actual sensor system inside the sensor 36. The cover layer 52 can, as shown here, Fig. 2 As indicated, it could be a rubber mat with nubs, such as those found on floor mats. The rubber mat covers the sensor 36 and protects it from external influences. At the same time, the rubber mat reinforces the housing 40, so that the use of the safety device 100 provides additional protection for the housing, which is not possible with a purely optical system.

[0063] Additionally, a further intermediate layer (not shown here) can be provided, which is arranged between the sensor 36 and the housing 40, more precisely the front side 46 of the housing. The intermediate layer can be made of a flexible, compressible material and can be scalable in size. The intermediate layer can serve to create a mechanical buffer zone corresponding to the machine's overrun from the time the sensor 36 is detected to the point where the machine 10 comes to a standstill, in order to prevent limbs from being crushed due to the overrun.

[0064] In a preferred embodiment, safe, tactile floor mats, such as those sold by the applicant under the name SafetyMat, can be used as sensors for the safety device 100. Since these already integrate all safety-relevant functions, they only need to be attached to suitable surface sections of the housing 40.

[0065] It is understood that the present invention is not limited to the pressure-sensitive sensors listed here, and that the principle of the safety device 100 can also be implemented with other sensors.

[0066] Fig. 3 shows a second embodiment of the safety device 100. Parts with the same reference numerals as in Fig. 2 refer to the same parts and will not be described again below.

[0067] The embodiment according to Fig. 3 differs from the embodiment according to Fig. 2 by the type of sensor 36. In the second embodiment, the sensor 36 is a capacitive sensor.

[0068] The capacitive sensor is shown here in a highly simplified manner. The principle of the capacitive sensor is based on the change in the electrical capacitance of a single capacitor or a capacitor system. In simplified form, such a capacitor is indicated here by a first electrode 54 and a second electrode 56.

[0069] In addition, the capacitive sensor has an oscillator 58 which is coupled to one of the electrodes 54, 56, which forms the frequency-determining capacitance of the oscillator 58. When an object, such as a section of the workpiece 26, approaches the electrode arrangement, this detunes the oscillator 58 in a measurable manner and a Fig. 2 described reaction can be triggered.

[0070] Furthermore, the design and arrangement of the electrodes 54, 56 allows a certain directional effect to be achieved, so that the sensor 36 essentially only registers an approach from the Z direction, as indicated here by the arrow with reference numeral 60. It is understood that in addition to the approach to the electrode 54, contact with it can also be registered by the capacitive sensor.

[0071] Particularly preferably, a part of the housing 40, as in Fig. 3 indicated, serve as the first electrode 54. In this way, the shape of the sensor surface 42 can be optimally adapted to the housing 40. Furthermore, in this embodiment, the sensor 36 does not extend beyond the housing 40 of the first machine part 12. All other components of the capacitive sensor can be arranged inside, protected by the housing 40. The capacitive sensor can further have a cover layer (not shown here) in order to achieve the same effect as in relation to the embodiment according to Fig. 2 has been described.

[0072] It is understood that the capacitive sensor may also be designed in a different shape, and the safety device 100 is not limited to the shape shown here.

[0073] Overall, it is conceivable that in a further embodiment, the different sensor technology according to the embodiments according to Fig. 2 and 3combined with each other. Furthermore, the principle can also be implemented with other sensors extending over a large area, provided they can detect contact or proximity to the sensor surface.

[0074] The safety device 100 is also not limited to the arrangement of the sensor 36 shown here on the first machine part 12. Rather, the sensor 36 can also be arranged on the second machine part 14 or at another location in the same way.

[0075] In this respect, the above-described embodiments do not limit the scope of the present invention. This scope is determined solely by the following claims.

Claims

1. Method for safeguarding a machine (10), in which a first machine part (12) executes a working movement along a first direction of movement (18) against a second machine part (14) in order to deform a workpiece (26) which has a section which, when the first machine part (12) acts, moves at least partially towards a front side (46) of the first machine part (12) or of the second machine part (14) in a second direction of movement (50) which crosses the first direction of movement (18), wherein a sensor (36) is arranged on a surface portion of the front side (46) of a housing (40) of the first machine part (12) or of the second machine part (14), having a sensor surface (42) extending over the surface portion, wherein the sensor (36) is being arranged on the surface portion such that it lies between the moving portion of the workpiece (36) and the housing (40), and the sensor surface (42) faces an operator of the machine (10), and wherein the sensor surface (42) registers an approach and / or a contact of the section of the workpiece (26) or an object connected thereto moving towards the first machine part (12) or the second machine part (14) and sends a signal to a controller, the controller triggering a safety-related action in response to the signal.

2. Method according to claim 1, wherein the sensor (36) is a pressure-sensitive sensor.

3. Method according to claims 1 or 2, wherein the sensor (36) comprises at least one electrode made of a textile material.

4. Method according to any one of claims 1 to 3, wherein the sensor (36) is a capacitive sensor.

5. Method according to claim 4, wherein the capacitive sensor comprises at least one electrode which is a part of the housing (40) of the first machine part (12) or the second machine part (14).

6. Method according to any one of claims 1 to 5, wherein the sensor (36) is a spatially resolving sensor configured to assign a location on the sensor surface (42) to the approach and / or the contact and to generate the signal to the controller based on this location assignment.

7. Method according to any one of claims 1 to 6, wherein the surface portion has an uneven surface and the sensor is adaptable to a contour of the uneven surface.

8. Method according to any one of claims 1 to 7, wherein the controller slows down and / or stops the working movement as a safety-related action.

9. Method according to any one of claims 1 to 8, wherein the sensor (36) is configured to distinguish between at least two stages of approach or contact and to report the respectively recognized stage to the controller.

10. Safety device (100) for safeguarding a machine (10), in which a first machine part (12) executes an working movement along a first direction of movement (18) against a second machine part (14) in order to deform a workpiece (26) which has a section which, when the first machine part (12) acts, moves at least partially towards a front side (46) of the first machine part (12) or of the second machine part (14) in a second direction of movement (50) which crosses the first direction of movement (18), the safety device comprising: a sensor (36) mountable on a surface portion of the front side (46) of a housing (40) of the first machine part (12) or the second machine part (14) and having a sensor surface (42) extending over the surface portion, wherein the sensor (36) is arranged on the surface portion such that it lies between the moving portion of the workpiece (36) and the housing (40) and the sensor surface (42) faces an operator of the machine (10), and wherein the sensor surface (42) is configured to register an approach and / or a contact of the workpiece (26) moving towards the first machine part (12) or the second machine part (14) or of an object connected thereto, to generate a corresponding signal and to transmit it to a controller.