The present invention generally relates to an electrical connector assembly having mateable contact pairs, and more specifically, to a connector assembly including predefined arcing zones located separate and apart from the final mating zones between blade and receptacle contacts.
In the past, ground and signal contact assemblies have been proposed that comprise pairs of mating receptacle and blade contacts. U.S. Patent No. 5,116,230 generally describes a make-first-break-last connector assembly provided by making ground pins of a pin header longer than signal pins of the header in order that the ground pins engage ground contacts of a mating connector before the signal pins engage signal contacts thereof. U.S. Patent No. 5,104,329 describes a connector assembly that uses ground plates, not ground pins, to afford a make-first-break-last connector assembly. U.S. Patent No. 5,169,324 discloses an electrical connector assembly in which a connector mounted on a circuit board has signal contact springs for mating with complimentary contact elements of a mating connector similarly mounted on the circuit board. A planar grounding blade projects beyond the signal contact spring for mating with a grounding contact of the mating connector.
U.S. Patent No. 5,582,519 discloses an alternative make-first-break-last connection. A pair of mating electrical ground contacts comprise a blade contact having a rearward blade support for retention in a first insulating housing and a contact blade projecting forwardly from the blade support, with a tab substantially narrower than the contact blade projecting forward from a forward edge of the contact blade. The pair of ground contacts comprises a receptacle contact having a rearward base for retention in an insolated housing and first and second contact springs projecting forwardly from the base. The first contact spring has a first transverse contact surface, while the second contact spring has a transverse contact surface that is substantially wider than the tab. The contact surfaces of the contact springs cooperate to apply contact forces to the tab and to the contact blade as the ground contacts are mated. The second contact spring defines a rearward opening for receiving the tab to allow full mating of the contact blade with the receptacle contact.
Connectors are being used in applications with higher and higher electrical performance demands, and thus improvement is needed to satisfy such demands. By way of example, today high performance connectors are in demand for applications such as telecommunications, computer systems requiring motherboard and daughter board connections, servers, networks, intemet applications and the like. These applications use connectors having separable interfaces that may be connected and disconnected repeatedly while still affording high signal performance characteristics.
More recently, the power and signal requirements have been extended to new levels, such as for example, but not limited to, power connectors capable of carrying 50 volt DC power supplies at 30 amps per contact. In addition, signal contacts are needed to carry signals rated in different rating tiers, such as at or near 2.5 GHz (Tier 1), 5 GHz (Tier 2), 10 GHz (Tier 3), and the like. An improved electrical connector assembly is needed to satisfy the higher power and signal requirements of today's applications.
In addition, connector assemblies are needed that better address the electrical phenomenon associated with "hot-plugging" or static electricity discharge. Hot-plugging refers to the process whereby the connector halves are mated while power continues to be applied to the board already mounted in the system. When cards or boards are added to the system while the power is on, arcing may occur. Another example is when circuit cards are stored before use, such cards collect static electricity. The collection of static electricity is not limited to motherboard and daughter card types of circuits. Instead, many other types of components and subassemblies have a tendency to collect static electricity during storage. The static electricity builds up in the component, card or subassembly until discharge to a ground. Typically these components are not grounded during storage, but instead are grounded for the first when inserted into a server, network, computer or other application. At the time that the card, component, subassembly and the like is inserted into a system, an electricity discharge may occur whether it be due to static electricity, hot-plugging or otherwise. In conventional connectors, the discharge occurs between the contacts at the mating interface where power or data signals are to be transferred to the card, component or subassembly once plugged into a server, network, computer and the like.
With today's high electrical signal and power performance requirements of matable connectors, the sensitivity of such connectors to electrical discharge is heightened. By way of example only, certain connectors may be coated at the mating interface with a material to facilitate the connection, such as gold plating and the like. However, the coating material becomes damaged and removed when arcing occurs since the coating material is not well suited to withstand the high voltage and/or current spikes that occur with hot-plugging or static electricity arc-type discharges. As the coating material degrades, the mating interface becomes susceptible to corrosion. As corrosion progresses, the resistance increases at the mating interface between the two connector halves of the contact assembly which in turn causes heating within the contacts. The chain of events (e.g., electrical discharge, corrosion, increased resistance and heating) induces an upper limit on the performance characteristics of the contact, such as by limiting the amount of power that the contact may handle and/or limiting the signal to noise characteristics maintainable by the contact for high data transmission speeds. In addition, as connectors are repeatedly unplugged and remated, the potential for additional build-up of a static electricity and discharge exists with each mating operation, thereby further exaggerating the foregoing problems.
A problem to be solved is how to provide a connector assembly that is capable of withstanding arcing in a manner that does not degrade the mating interface of the connector assembly.
This problem is solved by a connector assembly according to claim 1.
The invention is an electrical connector assembly including an insulated blade connector housing that holds a blade contact, and an insulated receptacle connector housing that holds a receptacle contact. The blade and receptacle connector housings are adapted to join in a mating operation during which the blade and receptacle contacts move from an initial mating position to a final mating position. The blade and receptacle contacts have mating portions that are arranged to electrically engage each other when the blade and receptacle contacts are in the final mating position. The receptacle contact has embossments that are arranged to engage the mating portion of the blade contact. The mating portions maintain a primary electrical interface between the blade and receptacle contacts. The blade and receptacle contacts also have respective arcing zones that are arranged to temporarily electrically communicate with each another when the blade and receptacle contacts are in the initial mating position to provide a temporary electrical interface between the blade and receptacle contacts.
The invention will now be described by way of example with reference to the accompanying drawings wherein:
Fig. 1 illustrates an exploded isometric view of a connector assembly oriented in a first direction and formed in accordance with at least one embodiment of the present invention;
Fig. 2 illustrates an exploded isometric view of a connector assembly oriented in a direction opposite the direction of Fig. 1, and formed in accordance with an embodiment of the present invention;
Fig. 3 illustrates a receptacle and blade connector pair formed in accordance with an embodiment of the present invention;
Fig. 4 illustrates a first side view of a portion of a receptacle connector formed in accordance with an embodiment of the present invention;
Fig. 5 illustrates a second side view of a portion of a receptacle connector formed in accordance with an embodiment of the present invention;
Fig. 6 illustrates a side sectional view of a receptacle connector taken along lines 6-6 in Fig. 4;
Fig. 7 illustrates a front view of a receptacle connector housing formed in accordance with an embodiment of the present invention;
Fig. 8 illustrates a sectional view taken lines 8-8 in Fig. 7 of a receptacle connector housing formed in accordance with an embodiment of the present invention;
Fig. 9 illustrates a blade contact and blade housing formed in accordance with an alternative embodiment of the present invention; and
Fig. 10 illustrates a receptacle contact and receptacle housing formed in accordance with an alternative embodiment of the present invention.
Fig. 1 and 2 illustrate an electrical connector assembly 10 from opposite ends formed in accordance with an embodiment of the present invention. The electrical connector assembly 10 includes an insulated blade contact housing 12 and an insulated receptacle contact housing 14 adapted to mate with one another to form a separable interface therebetween. The blade contact housing 12 frictionally retains a plurality of blade contacts 16, while the receptacle contact housing 14 frictionally retains a plurality of receptacle contacts 18.
During a mating operation, the blade contact housing 12 and receptacle contact housing 14 are joined by moving from an initial mated position to a final mated position. While in the initial mated position, a dedicated arcing zone of the blade and receptacle contacts 16 and 18 are the only portion of the contacts that engage one another to direct arcing to the designated zone, such as for the discharge of static electricity therebetween or hot-plugging. As the blade and receptacle contact housings 12 and 14 are further moved to final mated positions, the arcing zones may disengage, while primary interface regions of the blade and receptacle contacts 16 and 18 come into contact, and slidably engage one another in a pressure fit to support the flow of high current at high voltage therebetween, when used as power contacts, and to support the passage of data signals with a low SNR, when used as data signal contacts.
As shown in Fig. 1, the blade contact housing 12 includes front and rear faces 20 and 22, respectively. The blade contact housing 12 may be constructed as a right angle interface with a bottom face 24 adapted to be securely mounted to a structure such as a circuit board 26 designated in dashed lines. By way of example, the circuit board 26 may constitute a mother or daughter board, or any other card or component such as used in telecommunications applications, server applications, internet applications, computers and the like. The blade contact housing 12 includes a blade shroud 28 formed at one end. The bottom of the blade shroud 28 extends down over the edge of the circuit board 26. As better shown in Fig. 2, the shroud 28 houses knife portions 52 of the blade contacts 16 once frictionally secured within the receptacle contact housing 14 to engage the blade contacts 16.
The rear face 22 of the blade contact housing 12 includes a plurality of slots 30 formed therein and adapted to receive the blade contacts 16. Bottom edges 32 of the slots 30 include openings therethrough to permit the pins 34 on the blade contact 16 to project downward below the bottom edge 24. The pins 34 are securely mounted to through holes, vias, traces and the like on the circuit board 26. The slots 30 include notched channels 36 provided on at least one side of the slots 30 to receive anti-rotation bosses 38 provided on at least one side of the blade contacts 16.
The rear face 22 also includes a notch 40 extending transversely across the rear face 22 and located proximate the bottom face 24. The notch 40 is adapted to receive a stiffener bar 42 that joins multiple blade contact housings 12 prior to attachment to the circuit board 26. Joining multiple contact housings 12 may be desirable to present a package of connector assemblies, including both ground and signal connectors as a single assembly to customers. In addition, a larger U-shaped cut-out 45 is provided transversely across in the rear face 22. The cut-out 45 is notched deep enough such that, when the blade contacts 16 are fully inserted, the rear edges 46 are exposed in order that they may be utilized for assembly.
With reference to Figs. 1-3, the blade contact 16 may be formed as a single integral piece or from an assembly of parts. The blade contact 16 includes a main body 44 having a rear edge 46, a bottom edge 48, a top edge 50 and leading knife section 52 extending forward of the body 44. Pins 34 are formed with or secured to the bottom edge 48 and extend downward aligned in the plane containing the blade contact 16. The pins 34 may constitute compliant pins. Optionally, the pins 34 may be pins having a flared width in the direction of the thickness of (or perpendicular to the plane of) the blade contact 16, or shaped as eye-of-needle type pin. By providing a flared width, the pins 34 maintain a more secure friction fit within holes or vias in the circuit board 26. Optionally, the pins 34 may have compliant tails or tails that are soldered to the joining piece. In the embodiment of Fig. 1, the blade contact 16 is formed as a right angle contact, whereby the pins 34 are arranged at a right angle to the lead knife section 52. However, the blade contact 16 may be formed in other configurations and need not be a right angle contact.
The leading knife section 52 includes a primary mating region or portion 54 and an arc/lead arm 56 extending beyond the primary mating portion 54. The primary mating portion 54 includes a mating edge 58, while the arc/lead arm 56 includes a lead edge 60. The length of the knife section 52 and arc/lead arm 56 may vary to control the sequence in which contacts 56 are mated to control an order in which voltages are applied. The lead arm 56 includes arc zones 62 (Fig. 2) defined thereon and provided on at least one side thereof. The arc zones 62 may be formed in several manners, such as dimples, convex projections, or embossments stamped in the blade contact 16. Optionally, the arc zones 62 may be formed from plating, plates, coating and the like that are particularly resistive to the current and voltage spikes experienced during arcing and hot-plugging. In the embodiment if Figs. 1 and 2, the arc zones 62 represent dimples or embossments projecting toward the side of the blade contact 16 illustrated in Fig. 2. The side of the blade contact 16 illustrated in Fig. 1 shows the reverse side of the dimples as divots 64.
The blade contact housing 12 and receptacle contact housing 14 separately may be formed as individual integral pieces, such as through injection molding and the like.
The receptacle contact housing 14 includes a front face 72, a rear face 74, a top side 76 and a bottom side 78. The top and bottom sides 76 and 78 are formed with top and bottom channels 80 and 82, respectively, which extend from the front face 72 rearward to form ribs 81 and 83 therebetween. The top and bottom channels 80 and 82 cooperate with similar features inside of the blade shroud 28 to ensure proper orientation and alignment between the blade and receptacle contact housings 12 and 14 during the mating operation.
More specifically, as illustrated in Fig. 2, the blade shroud 28 defines a cavity 84 into which extend the leading knife sections 52 of the blade contacts 16. Interior top and bottom surfaces 86 and 88 of the blade shroud 28 include a plurality of ribs 90 having channels 92 therebetween extending from the front face 20 backward into the cavity 84. The ribs 90 and channels 92 cooperate with the bottom channels 82 and ribs 83 and top channels 80 and ribs 81 on the receptacle contact housing 14 to ensure proper orientation and alignment therebetween when mated. While not illustrated, the top surface 86 includes ribs and channels similar to ribs 90 and channels 92. Optionally, leading ends of the top and bottom channels 80 and 82 may be beveled to facilitate engagement with the ribs 90.
Returning to Fig. 1, the receptacle contact housing 14 includes a plurality of slots 94 cut therethrough oriented vertically, aligned parallel to one another and extending between the front and rear faces 72 and 74. Lead openings 96 of the slots 94 are beveled to facilitate acceptance of corresponding leading knife sections 52 of each blade contact 16.
With reference to Fig. 2, the rear face 74 of the receptacle contact housing 14 includes the rear openings 98 of the slots 94 which extend entirely through the receptacle contact housings 14. The rear openings 98 are configured with thin bottom and top channels 100 and 102 and a wider midsection 104. A central bevel 106 is cut along one side of each slot 98. The bottom and top channels 100 and 102, midsection 104 and bevel 106 cooperate to accept the various features of the receptacle contacts 18.
Turning to Fig. 3, exemplary blade and receptacle contacts 16 and 18 are illustrated. The receptacle contact 18 may be stamped from a single piece of material or molded or the like. The receptacle contact 18 includes a generally rectangular main body 110 having a length 112 and a width 114 determined based upon the power and/or signal performance requirements. As higher power demands are placed on the receptacle contact 18, the width 114 may be varied. For instance, to afford high current carrying capacity, it may be desirable to provide a width 114 that is as large as permitted by the overall envelope of the receptacle contact housing 14 to provide the maximum area for current flow. By increasing the width 114, additional pins 116 may be added further adding to the current flow capacity.
The main body 110 includes a leading edge 118 and a rear edge 120. The pins 116 are formed on and extend rearward from the rear edge 120. Optionally, the pins 116 may be compliant pins or compliant tails may be action pins, such as with a flared width extending in the direction of the thickness of the main body 110 to enhance frictional engagement of the pins 116 with a circuit card or the like (not shown) that is frictionally affixed thereto. Optionally, pins 116 and 34 may be tails that are soldered or press fit into circuit boards. The main body 110 includes retention embossments 122 stamped therein which frictionally engage interior surfaces within the bottom and top channels 100 and 102 to retain the receptacle contacts 18 in the receptacle contact housing 14. Extending from the lead edge 118 is a mating portion or contact assembly 124.
In the embodiment of Fig. 3, the contact assembly 124 includes a plurality of spring contact arms aligned to define a thin elongated planar gap 126 therebetween that receives the leading knife section 52 of the blade contact 16. A U-shaped contact arm 128 and a pair of cantilevered contact beams 130 are provided as part of the contact assembly 124 and are aligned to define the gap 126 therebetween. The U-shaped contact arm 128 includes a pair of contact springs 134 and 136 each having bent portions 138 and 140, respectively, at the bases thereof. Outer ends of the contact springs 134 and 136 are joined by a strap 142 having a transverse leading edge 144 that is flared outward. The contact springs 134 and 136 are spaced apart to define an opening 164 therebetween that receives the knife section 56 when moved beyond the initial mating position to the final mating position.
The cantilevered contact beams 130 also includes leading edges 146 that are flared outward away from leading edge 144 to guide the blade contact 16 therebetween. A center portion of the strap 142 is configured to operate as an arc zone 148. The arc zone 148 engages the arc zone 62 on the blade contacts 16.
Embossments 150 are also provided on the U-shaped contact arm 128 separate and apart from the arc zone 148. The embossments 150 may be coated with a material to facilitate conduction, such as gold plating and the like. The embossments 150 contact the primary mating portion 54 of the leading knife section 52 on the blade contact 16 when the contacts are in a fully mated position. In addition, embossments 152 may be provided on the cantilevered contact beams 130 and arranged to engage the primary mating portion 54 (on the side opposite of the embossments 150) when in a final mated position. Embossments 152 may also be plated with a material to facilitate conduction, such as gold and the like. The embossments 150 and 152 afford multiple contact points between the primary mating portion 54 and the receptacle contact 18 and thereby facilitate current flow and improve the power carrying capacity of the mated contacts. As the pressure is increased at the primary mating sections 54, the resistance of the interface decreases and enables more current to flow without heating.
Figs. 4 and 5 illustrate opposite sides of the contact assembly 124 to better illustrate the embossments 150 and 152. In Fig. 4, the contact assembly 124 is oriented to show the blade engaging face 156 of the U-shaped contact arm 128 and backsides 158 of the contact beams 130. Fig. 5 illustrates the contact assembly 124 oriented in the reverse direction as compared to the illustration of Fig. 4. In Fig. 5, the contact assembly 124 is oriented to illustrate the blade engaging faces 160 of the contact beams 130 and backsides 162 of the contact arm 128. Embossments 152 are formed on the blade engaging faces 160 of the contact beams 130, while the embossments 150 are located on the blade engaging face 156 of the contact arm 128.
Fig. 6 illustrates a side view of a receptacle contact 18 showing the profiles of the contact arm 128 and contact beams 130 with the gap 126 provided therebetween. The illustration of Fig. 6 represents a side sectional view taken along line 6-6 in Fig. 5.
Fig. 7 illustrates a front view of a receptacle contact housing 14 with receptacle contacts 18 mounted therein. In the example of Fig. 7, the receptacle contact housing 14 is provided with four slots 94 for acceptance receptacle contacts 18, however a different member of slots may be used.
Fig. 8 represents a sectional view of the receptacle contact housing 14 of Fig. 7 taken along line 8-8. Fig. 8 illustrates the contour of the slots 94 and lead openings 96 in more detail.
During a mating operation, the blade and receptacle housings 12 and 14 are moved to an initial mated position in which the lead edge 60 of each blade contact 16 is accepted within corresponding slots 94 and engages the arc zone 148 of the contact assembly 124. When the arc zones 62 and 148 engage one another, while at the initial mating position, any static electricity buildup in the circuit board 26 (or in the circuit board mounted to the receptacle contact 14) or hot-plugging power is discharged. The arc zones 62 and 148 are constructed to exhibit a high tolerance for the electrical characteristics associated with hot-plugging and a static electricity discharge, such as a high current or voltage spikes.
As the blade and receptacle contact housings 12 and 14 are moved from the initial mating position, the lead arm 56 extends into and slides through the opening 164 defined in the center of the U-shaped contact arm 128. As the lead arm 56 moves into the opening 164, the arc zones 62 and 148 disengage. Simultaneously or shortly thereafter, the embossments 152 on the cantilever beams 130 engage an opposite side of the lead arm 56 designated in Fig. 3 as mating zone 168. The embossments 152 slide along the mating zone 168 until the blade and receptacle contacts 16 and 18 are moved to a final mated position.
When in the final mated position, the embossments 152 electrically engage a final mating face 170 on the leading knife section 52 of the blade contact 16. Also, the embossments 150 electrically engage an opposite final mating face 172 on the leading knife section 52 of the blade contacts 16. When in the final mated position, the cantilever beams 130 and contact arms 134 and 136 apply substantially equally and opposite forces upon opposite sides of the blade contact 16. Through application of these equal but opposite forces, the contact assembly 124 maintains a firm electrical interface with the knife section 52 of the blade contact 16.
During a mating operation, blade and receptacle mating zones may only engage one another after the initial mating position and thereafter maintain a primary electrical interface between the blade and receptacle contacts. Blade and receptacle arcing zones may temporarily engage one another when in the initial mating position and thereafter be disengaged as the blade and receptacle contacts are moved from the initial mating position to the final mating position. The blade and receptacle arcing zones and/or mating zones may be formed as raised dimples provided at desired regions of the contacts. For instance dimples intended to supply power are located in power interface regions on the contacts, while dimples intended to serve as static electricity discharge points are located in arcing regions separate and remote from the interface regions. Optionally, the raised bumps intended for arcing may be located in a sacrificial portion of an associated one of the blade and receptacle contacts. Optionally, the strap 142 may be formed as a cross bar separate from or integral with the contact springs 134 and 136.
Fig. 9 illustrates a blade contact 216 and blade contact housing 212 formed in accordance with an alternative embodiment. The blade contact housing 212 includes a slot 230 formed in the rear face 220 proximate the top surface 221. A second notch 233 is provided across the rear end of the top surface 221. Slots 230 and 233 receive retention bars to facilitate the combination of multiple blade contact housings 212 of different shapes and sizes and blade/signal configurations.
Fig. 10 illustrates a receptacle contact housing 214 and receptacle contact 218 formed in accordance with an alternative embodiment. Opposite sides 213 and 215 of the receptacle contact housing 214 are provided with ribs 217 that cooperate with corresponding channels 219 (Fig. 9).
Optionally, the pins 116 may be spaced different distances 154 apart to ensure proper orientation when inserted.
Optionally, the number of contact arms used within the contact assembly 124 may be modified to includes more or fewer cantilever beams 130 on either or both sides. Alternatively, U-shaped contact arms may be afforded on both sides of the blade contact 16, but staggered to ensure that arcing zones engage first on the receptacle and blade contact 16 and 18 before the primary mating interfaces.
Optionally, the arcing zones may be configured in a variety of shapes and structures. For instance, the arcing zones may not include embossments. Alternatively, the arcing zone 148 may include embossments, while the arcing zone 62 may not. Optionally, both arcing zones 52 and 148 may includes embossments. Optionally, the embossments 150 and 152 may be provided in a variety of shapes and sizes. For instance, more than four or fewer than four embossments may be used. Multiple embossments may be used on each contact arm. The shape of the embossment may be varied and the location thereof may be changed. The embossments 150 and 152, optionally, may be constructed separately from the contacts and provided thereon during the manufacturing process, such as through screws, gluing, coating and arc resistant material and the like on the contacts.
Elektrische Verbinderanordnung, die aufweist: ein isoliertes Messerverbindergehäuse (12), das einen Messerkontakt (16) hält; und ein isoliertes Buchsenverbindergehäuse (14), das einen Buchsenkontakt (18) hält, wobei das Messer-und das Buchsenverbindergehäuse so angepaßt sind, daß sie sich in einem Eingriffsvorgang verbinden, während dessen sich der Messer- und der Buchsenkontakt von einer anfänglichen Eingriffsposition in eine endgültige Eingriffsposition bewegen, wobei der Messer- und der Buchsenkontakt Eingriffsabschnitte (54, 124) aufweisen, die so angeordnet sind, daß sie elektrisch miteinander in Eingriff kommen, wenn sich der Messer- und der Buchsenkontakt in der endgültigen Eingriffsposition befinden, wobei die Eingriffsabschnitte eine primäre elektrische Anschlußfläche zwischen dem Messer- und dem Buchsenkontakt aufrechterhalten, worin der Messer- und der Buchsenkontakt entsprechende Funkenüberschlagszonen (62, 148) aufweisen, die angeordnet sind, um zeitweilig elektrisch miteinander in Verbindung zu kommen, wenn der Messer- und der Buchsenkontakt in der anfänglichen Eingriffsposition sind, um eine zeitweilige elektrische Anschlußfläche zwischen dem Messer- und dem Buchsenkontakt zu bewirken,
dadurch gekennzeichnet, daß
der Buchsenkontakt Buckel (150, 152) aufweist, die so angeordnet sind, daß sie mit dem Eingriffsabschnitt (54) des Messerkontaktes in Eingriff kommen, wenn sich der Messer- und der Buchsenkontakt in der endgültigen Eingriffsposition befinden.
2. Elektrische Verbinderanordnung nach Anspruch 1, bei der der Messerkontakt Buckel (64) in der Funkenüberschlagszone (62) aufweist.
3. Elektrische Verbinderanordnung nach Anspruch 1 oder 2, bei der der Buchsenkontakt ein Paar Kontaktfedern (134, 136) mit äußeren Enden aufweist, die mittels eines Bügels (142) verbunden sind, und wobei der Bügel die Funkenüberschlagszone (148) des Buchsenkontaktes bildet.
4. Elektrische Verbinderanordnung nach Anspruch 3, bei der die äußeren Enden der Kontaktfedern Buckel (150) aufweisen, die so angeordnet sind, daß sie mit dem Eingriffsabschnitt (54) des Messerkontaktes in Eingriff kommen, wenn sich der Messer-und der Buchsenkontakt in der endgültigen Eingriffsposition befinden.
5. Elektrische Verbinderanordnung nach einem der Ansprüche 1 bis 4, bei der der Buchsenkontakt einen Kontaktarm (128) und ein Paar Kontaktträger (130) umfaßt, die vom Kontaktarm (128) durch einen Spalt (126) beabstandet sind, der so dimensioniert ist, daß der Eingriffsabschnitt (54) des Messerkontaktes aufgenommen wird.